How could hundreds of clearings of the OBD codes cause the catalytic I/M readiness monitor to set?

[mike]

How could 50 to 100 clearings of the OBD codes (using a dumb OBD reader)
cause the catalytic I/M readiness monitor to set after months of not
setting?

Can the complicated electronics modules be "saving" scores of prior memory
sessions perhaps?

The storey is a bit confusing because the pieces only fell in together well
after the fact for each event, but here's the short summary of what
happened as I loosely recall the major happenstances of this purely
electronic ordeal.

[1] The check engine light has been on, on the dash, almost constantly
[2] Mostly when I looked, it would be P0420 bad cat pending & set codes
[3] I've been going through this regimen now, for about five or six years
[4] I didn't need smog for more than a year so I didn't worry about codes
[5] When it came within months of smog time, I cleared the OBD codes
[6] Mostly either the code comes back or the readiness monitor won't set
[7] But once in a while, the readiness monitor does set so I rush to smog
[8] I did that - it passed smog - but failed for a hose in bad condition
[9] I painted the hose black so that it would look like it's brand new
[10] But then for another month I couldn't get the readiness monitor to set
[11] At one point, I accidentally added gasoline with water (long story)
[12] The car ran like hell for an entire gas tank until I refilled it

After that, it passed smog and for months now, no codes.
What happened?
I have no clue.

A miracle?
A coincidence?

I do not know.

Maybe what "might" have happened is that during the time that I was driving
on the tank of watery gas, I had to keep the OBD code clearer on my lap.

Within a mile, the engine would stumble and I'd clear the codes and the
engine would run fine for another mile, and then it would stumble, and then
I'd clear the code and it would run fine for another mile, and so on.

This I did for at least a hundred, maybe two hundred maybe three hundred
times during the watery gas stage - but - miracles to happen I guess
because after that, no codes and, get this, the readiness monitors all set.

I passed at a different smog station (with the painted hose to make it look
like new not being an issue) and now I'm just wondering what the heck
happened?

Can it be that there is some kind of multiple instance "persistent memory"
inside one of the engine computers that I finally wiped out by clearing the
codes hundreds of times in a row?

[Bob F]

Or, did the water clean up the catalyst?

[Scott Dorsey]

In article <u23gk5$3lpeo$1...@solani.org>, mike <th...@address.is.invalid> wrote:
>How could 50 to 100 clearings of the OBD codes (using a dumb OBD reader)
>cause the catalytic I/M readiness monitor to set after months of not
>setting?

It cannot. But the fact that you've got 50 to 100 clearings of the OBD codes
makes your general maintenance process very suspect.

>[1] The check engine light has been on, on the dash, almost constantly
>[2] Mostly when I looked, it would be P0420 bad cat pending & set codes
>[3] I've been going through this regimen now, for about five or six years
>[4] I didn't need smog for more than a year so I didn't worry about codes

What this means is that the O2 sensor downstream of your converter is
reading an incorrect value. This could mean your converter is bad, or
maybe that the O2 sensor is bad, or maybe that the connector is bad.

If other codes were set too, it could have been all kinds of other things.
If you're seeing incorrect values on both pre and post converter
sensors, you'll see other codes, and that could be the result of all kinds
of misfiring issues or mixture control issues.

>[5] When it came within months of smog time, I cleared the OBD codes
>[6] Mostly either the code comes back or the readiness monitor won't set
>[7] But once in a while, the readiness monitor does set so I rush to smog

Have you considered actually finding and fixing the problem instead of
constantly resetting the error? You're not doing your engine or your
gasoline bill any good this way.

>[8] I did that - it passed smog - but failed for a hose in bad condition
>[9] I painted the hose black so that it would look like it's brand new

Wow, with maintenance like that it's a wonder your car runs at all.

>[10] But then for another month I couldn't get the readiness monitor to set
>[11] At one point, I accidentally added gasoline with water (long story)
>[12] The car ran like hell for an entire gas tank until I refilled it
>
>After that, it passed smog and for months now, no codes.
>What happened?
>I have no clue.

Maybe the converter was dirty and all the steam cleaned it out. Maybe you
had a fouled plug which was causing a misfire and the steam cleaned it up.
Maybe you had a bad vacuum hose and the warmer weather caused it to seal up.

Since you didn't actually find the problem when you had the code coming up,
and you made no attempt to do actual diagnosis, it's hard to tell after the
fact.

>Within a mile, the engine would stumble and I'd clear the codes and the
>engine would run fine for another mile, and then it would stumble, and then
>I'd clear the code and it would run fine for another mile, and so on.
>
>This I did for at least a hundred, maybe two hundred maybe three hundred
>times during the watery gas stage - but - miracles to happen I guess
>because after that, no codes and, get this, the readiness monitors all set.

As my father always said, "machines that fix themselves always break
themselves again."

>Can it be that there is some kind of multiple instance "persistent memory"
>inside one of the engine computers that I finally wiped out by clearing the
>codes hundreds of times in a row?

You are too fixated on the codes popping up and making no attempt to ask
WHY the codes were popping up and what was actually going on. Stop worrying
about the damn codes and start worrying about how the engine is running.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[mike]

On 23-04-2023 21:04 Bob F <bobn...@gmail.com> wrote:

> Or, did the water clean up the catalyst?

That's a good question.
Is there some chemistry that running water through the cat cleans it up?

The water issue was new as that was a complete accident that I had an empty
tank and I had to take someone to the airport all of a sudden so I used a
five gallon container of gas that was outside and it turned out to be old
and it happened to have a lot of water in it as the cap was leaking inward.

The 2004 Mitsubishi Lancer 4-cylinder tiny engine has always had this
problem since I bought it as the previous owner sold the entire car to me
for $200 knowing it needed a new catalytic converter & much other stuff.

A mechanic told him that was the reason for the P420 code, but what I did
when I got the car was put a new oxygen sensor in and that helped for a
couple of years to get it through smog but it still is hard to set the
readiness monitors. I know all about the drive cycle but it's got nothing
to do with that as it takes months of use to set the readiness monitors.

Only two things have ever set the readiness monitors for me, one of which
was to drive for a few hundred miles at one stretch, and back, which
shouldn't do anything (because I know what a drive cycle entails).

The other thing happened to be the water in the gasoline fiasco, where the
tank is something like ten or so gallons, but I put in five gallons of a
gas:water mix, which I used up and then refilled with clean gasoline.

Once the codes see a misfire of 1 in 200 revolutions, the engine control
module turns off the electricity to that spark plug, and the only way to
turn it back on is either to shut down the car or reset the codes.

It turns out that clearing the codes while driving works perfectly. There
is a seven second delay between stumbling, clearing, and the codes gone.

I know this because I had the OBD tester in my lap for hundreds of miles
over a period of a couple weeks where I reset the code I don't know how
many times, but probably a few hundred times in a single tank of gas.

What's weird is that this issue of the P0420 cat code and the inability to
reset the cat read monitor has happened for many years (probably three
smogs, so that's six years) but its character changed completely after the
water-in-the-gas fiasco with the hundreds of reset actions.

Now there is no P0420 code and the readiness monitor set it self nicely.
How did that happen?

I was thinking that there might be a database inside the engine control
modules of the last fifty or so codes, where I used them all up by clearing
more than those fifty or so times, but your idea that the water in the gas
chemically cleaned out the cat sounds better as it's kind of like a
'seafoam' treatment, of sorts.

Is there any chemistry backing up that idea that the water cleaned the cat?

[mike]

On 23-04-2023 15:56 Scott Dorsey <klu...@panix.com> wrote:

>>How could 50 to 100 clearings of the OBD codes (using a dumb OBD reader)
>>cause the catalytic I/M readiness monitor to set after months of not
>>setting?
>
> It cannot. But the fact that you've got 50 to 100 clearings of the OBD codes
> makes your general maintenance process very suspect.

The question isn't about how horrible a person I am but whether or not
running gas:water could have (probably temporarily) increased the
efficiency of an old cat (or whether clearing an engine control unit buffer
could have enabled the cat readiness monitor to be more easily set).

As for your negative comment about my maintenance skills, I must not have
been clear although I thought I was detailed enough with the dozen steps
listed. I don't care about the cat efficiency unless I have to smog.

Then, all of a sudden, I care about two things
[1] I care that there are no pending or set codes (especially P0420)
[2] I care that the readiness monitors are set (especially the cat)

You don't seem to know engines well, so allow me to explain that when the
engine sees a misfire in 1 out of 200 revolutions (most cars), the engine
control module permanently shuts down the spark to that cylinder (to
protect the cat).

This is permanent.

[1] The engine is running but at some point the engine noticeably stumbles
[2] The CEL goes on and the cylinder will be off forever
[3] Even if you drive for the 300 miles or so that the gas tank can do

There are only 2 things that will undo that permanently shut off cylinder.
[1] Either you turn the engine off and start it back
(in which case the code is still there but the spark is back again)
[2] Or you clear the codes
(in which case the code is gone and the spark is back to that cylinder)

Then the cycle repeats anew.

This is well known so if you don't know it you just don't know engines well
and that's fine because this question is about the cat and not the engine.

Could the water:gas mixture, somehow, have increased the cat efficiency?
Could the hundreds of code clearings, somehow, have wiped out a buffer?

>>[1] The check engine light has been on, on the dash, almost constantly
>>[2] Mostly when I looked, it would be P0420 bad cat pending & set codes
>>[3] I've been going through this regimen now, for about five or six years
>>[4] I didn't need smog for more than a year so I didn't worry about codes
>
> What this means is that the O2 sensor downstream of your converter is
> reading an incorrect value. This could mean your converter is bad, or
> maybe that the O2 sensor is bad, or maybe that the connector is bad.

When I got the Mitsubishi Lancer 2004 for $200 it had this problem then.
I replaced the oxygen sensor (there appears to only be one upstream sensor)
and that alone fixed the problem for the first smog about 5 or 6 years ago.

There are no oxygen sensor codes.
I need to repeat that because the oxygen sensor is not showing any codes.

That means the oxygen sensor is getting the correct voltage, the wires are
fine (although there could be an intermittence I guess), and the input and
output are fine.

I repeat there are no oxygen sensor codes.
Therefore, I see no reason to suspect the oxygen sensor on a mere whim.

I've noticed a lot of people replace the sensor whenever they get a code
but that's what the tests are for on the sensor itself. If the sensor were
bad, it would show a code of a bad input, output, or power connection.

It doesn't.

> If other codes were set too, it could have been all kinds of other things.
> If you're seeing incorrect values on both pre and post converter
> sensors, you'll see other codes, and that could be the result of all kinds
> of misfiring issues or mixture control issues.

It's only the P0420 and there is only one bank so it's for the cat.

"The P0420 code signals a low catalyst system efficiency. This code
suggests that the oxygen levels are below the desired threshold (Bank 1),
which most often results from problems with your car's exhaust or fuel
systems."

I'm sure it's the cat.
I just don't want to replace the cat.

And, get this, it passes smog without me doing anything but clearing the
P0420 code and letting the readiness monitors (especially for the cat) set.

The problem isn't passing smog because it generally took a few months of
driving to finally set the readiness monitors after clearing.

The question is only whether clearing the codes hundreds of times allowed
some kind of "buffer" to be wiped out in the engine control module - or -
as someone else suggested - maybe the water in the gas increased the
efficiency (somehow? chemically?) of the catalytic converter?

>
>>[5] When it came within months of smog time, I cleared the OBD codes
>>[6] Mostly either the code comes back or the readiness monitor won't set
>>[7] But once in a while, the readiness monitor does set so I rush to smog
>
> Have you considered actually finding and fixing the problem instead of
> constantly resetting the error? You're not doing your engine or your
> gasoline bill any good this way.

There is no problem other than the cat is the original 2004 and it has low
efficiency, and, as a result, every once in a while the P0420 pops up and
the readiness monitor for the cat takes hundreds of miles for it to set.

>>[8] I did that - it passed smog - but failed for a hose in bad condition
>>[9] I painted the hose black so that it would look like it's brand new
>
> Wow, with maintenance like that it's a wonder your car runs at all.

There was absolutely nothing wrong with the hose & it's expensive to
replace. It passes smog. It would have cost about $100 bucks to replace.

Painting it accomplished essentially the same function as replacing it
given there was nothing functionally wrong with the hose at that time.

It just didn't pass a visual inspection. I would have passed it. He didn't.
He wanted me to do a repair right then and there at his gas station.

I refused. I think he just wanted business by claiming the hose was bad.
There was nothing I could do other than pay him and never go back there.

There was nothing wrong with the hose from a functional standpoint.
If it actually fails, then I'll replace it. But I'll wait for it to fail.

It doesn't seem like you understand engines at all by the comments you're
making. This is a car that cost $200 five or six years ago. Not a Tesla.

It has an old 2004 tired low efficiency catalytic converter. That's all.

If I'm not going to replace a hose that isn't broken, I'm certainly not
going to replace a catalytic converter that isn't broken either.

It passes smog.
It just throws a low efficiency code for the cat.

Once in a while.

>>[10] But then for another month I couldn't get the readiness monitor to set
>>[11] At one point, I accidentally added gasoline with water (long story)
>>[12] The car ran like hell for an entire gas tank until I refilled it
>>
>>After that, it passed smog and for months now, no codes.
>>What happened?
>>I have no clue.
>
> Maybe the converter was dirty and all the steam cleaned it out. Maybe you
> had a fouled plug which was causing a misfire and the steam cleaned it up.
> Maybe you had a bad vacuum hose and the warmer weather caused it to seal up.

I don't think you understand engines as there couldn't possibly have been a
"fouled plug" as that's just shooting in the air hoping to hit the moon.

It's not a vacuum hose either as that would have thrown a different code.
Probably a P0171 or similar lean engine condition which is a common fault.

If you keep shooting at the moon, you might hit it, but that's not the kind
of guesses I was hoping to get as to how either the hundreds of resets
alone, or the bad gas alone, or the combination, caused the apparently
(probably temporary) fixing of a low efficiency catalytic converter code.

> Since you didn't actually find the problem when you had the code coming up,
> and you made no attempt to do actual diagnosis, it's hard to tell after the
> fact.

You never asked me what diagnostics I've run, where I _believe_ that the
code is telling me the truth, which is that the cat is low efficiency at
intermittent stages.

You're just shooting at the moon hoping you'll hit it while I'm believing
EVERYTHING the car is telling me. The OBD codes are telling me that the cat
is low efficiency sometimes and I believe it. Why wouldn't I believe it?

It's not the oxygen sensor as I replaced it and I tested the old one with a
burner flame and it read in the range that was to be expected of it.

I don't know why I have trouble setting the readiness monitor for the cat,
but I "suspect" (yes, I am assuming) that it's due to the low efficiency.

>>Within a mile, the engine would stumble and I'd clear the codes and the
>>engine would run fine for another mile, and then it would stumble, and then
>>I'd clear the code and it would run fine for another mile, and so on.
>>
>>This I did for at least a hundred, maybe two hundred maybe three hundred
>>times during the watery gas stage - but - miracles to happen I guess
>>because after that, no codes and, get this, the readiness monitors all set.
>
> As my father always said, "machines that fix themselves always break
> themselves again."

I think you missed the part about that being caused by water in the gas.
The water, if that's what cleaned out the cat, turned out to be a boon.

>>Can it be that there is some kind of multiple instance "persistent memory"
>>inside one of the engine computers that I finally wiped out by clearing the
>>codes hundreds of times in a row?
>
> You are too fixated on the codes popping up and making no attempt to ask
> WHY the codes were popping up and what was actually going on. Stop worrying
> about the damn codes and start worrying about how the engine is running.

I find it incredulous that you think I'm fixated on the "codes popping up",
where I'm _believing_ everything the codes are telling me. Everything.

[1] The cat, sometimes, is low efficiency
[2] The cat readiness monitor, after clearing, takes a long time to set

I believe exactly what the codes are telling me.
I did all the diagnostics long ago and there's nothing to do but replace
the cat if I cared about the low efficiency and readiness monitors.

The only time I care about either of them is when I need to pass smog.
Which I _always_ do pass - except when the hose looks ugly that is.

The question here isn't how horrible a person I am and how great you are.
The question is simply what caused the complete change of character.

Did the water in the gas have any chance of chemically "cleaning" out the
cat such that it suddenly became more efficient (probably temporarily) as
one person suggested?

Or, maybe did just clearing out the buffer of fifty or so prior codes
stored in the engine control module enable the readiness monitor to be set?

[Peter Moylan]

On 24/04/23 04:48, mike wrote:
> Only two things have ever set the readiness monitors for me, one of which
> was to drive for a few hundred miles at one stretch, and back, which
> shouldn't do anything (because I know what a drive cycle entails).

You seem to be right at the inflection point of the cat efficiency, so
almost anything that affects its efficiency will cause your symptoms.

That means your real question, whether you know it yet or not, is what can
increase/decrease the efficiency of a catalytic converter in operation?

Taking your long drive example, I think that long drive might have heated
the cat to the point that maybe that heat temporarily increased its
chemical efficiency. Maybe the same thing happens with water in the gas?

Or, maybe it's not the water in the gas but the fact that the water caused
the cylinder to shut off which caused gas to flow over the cat which might
have again heated up the cat enough to temporarily increase its efficiency?

You only threw a little gas onto the cat because you kept resetting the
codes so you threw gas on the cat, and then you ran normally hot, and then
you again threw gas on the cat, & you repeated that cycle many times over.

Maybe that heat:cool:heat:cool:heat:cool:heat:cool cycle increased the
efficiency of the cat just enough over a threshold to stabilize the system?

All indicators are that you're on the cusp of catalytic efficiency, where
98% of the time or thereabouts you're just efficient enough, but under some
conditions that you need to figure out (usually temperature & humidity),
you're below efficiency.

Then the code is set which will reset on its own within three drive cycles.
But once you clear the code, you have to wait for cat readiness to be set.

If you have the time for your next smog, I suggest you do NOT clear the
codes (because then you add the second readiness monitor to the mix), but
that you let the drive cycle (usually around 50 miles) clear it for you.
--
Peter Moylan

[PietB]

mike wrote:

> "The P0420 code signals a low catalyst system efficiency. This code
> suggests that the oxygen levels are below the desired threshold (Bank 1),
> which most often results from problems with your car's exhaust or fuel
> systems."
>
> I'm sure it's the cat.
> I just don't want to replace the cat.

Technically, you only need to replace the front of the cat, not the back.
(:->)

You can narrow down the problem even further by knowing that only the NOx
"light off" brick in the front of the cat is monitored by the OBD system.
https://www.carparts.com/blog/p0420-code-catalyst-system-efficiency-below-threshold-bank-1-2-2/

That "light off" brick stores oxygen it separates from the NOx vapors.
The HC/CO catalyst brick behind it is not monitored by the OBD system.

So your problem is probably limited only to the front NOx section alone.

"The Upstream O2 signal switches very rapidly in response to Fuel Trim
(several times a second). The O2 sensor behind the light-off catalyst (the
Downstream Sensor) is also monitoring oxygen, but if the light-off (NOx)
catalyst is storing oxygen properly (meaning the catalyst is healthy), the
rear O2 sensor signal will be very lazy when compared to the upstream O2.
When the ECM/PCM sees the downstream O2 sensor switching at or near the
same rate as the upstream O2 sensor, it sets the P0420 code."

To do its job, the front "light off" NOx catalyst brick has to be hot.
And it has to be able to store enough oxygen to add it to the NOx vapors.

If anything you did makes that front NOx "light off" brick get hotter or
store more oxygen, then you'd be experiencing the effect that you've seen.

-p

[Bob F]

Would any electrically controlled fuel injection engine continue to
inject fuel into a cylinder to which it had cut off spark?

[Scott Dorsey]

In article <u23pvm$3s6ne$1...@solani.org>, mike <th...@address.is.invalid> wrote:
>On 23-04-2023 15:56 Scott Dorsey <klu...@panix.com> wrote:
>
>Could the water:gas mixture, somehow, have increased the cat efficiency?

Certainly. All that steam in there could have cleaned the converter out.
But it ALSO could have cleaned out the downstream O2 sensor. And it might
have temporarily cleaned something completely unrelated too.

>Could the hundreds of code clearings, somehow, have wiped out a buffer?

No.

>> What this means is that the O2 sensor downstream of your converter is
>> reading an incorrect value. This could mean your converter is bad, or
>> maybe that the O2 sensor is bad, or maybe that the connector is bad.
>
>When I got the Mitsubishi Lancer 2004 for $200 it had this problem then.
>I replaced the oxygen sensor (there appears to only be one upstream sensor)
>and that alone fixed the problem for the first smog about 5 or 6 years ago.
>
>There are no oxygen sensor codes.
>I need to repeat that because the oxygen sensor is not showing any codes.

You have a downstream sensor, and you know that because you got a P0240.

Check what the P0240 code means. It means that the downstream O2 sensor
is not getting the correct value. Since you aren't getting any other codes,
you can assume the upstream O2 sensor is getting the correct value, and
that the engine stoichometry is good but that the gas coming out of the
converter is not good.

That is why the P0240 sensor implies a bad converter.

How bad is the converter? Is the issue the converter itself or the
measurement? The code does not tell you. If you have a proper scanner you
can look at the actual values of the oxygen sensors. You can see that
they are in range, that they are settling in quickly, and how well they
track one another. This is how you determine whether it's a sensor or the
converter or both.

If you do not have a proper scanner you are working blind and all you can do
is measure the converter temperature with an IR thermometer and make sure
it's getting up to temperature properly. If it's too cold, it's not working.
This is a very crude measurement.

>I repeat there are no oxygen sensor codes.
>Therefore, I see no reason to suspect the oxygen sensor on a mere whim.

The P0240 -is- a downstream oxygen sensor code.

>I've noticed a lot of people replace the sensor whenever they get a code
>but that's what the tests are for on the sensor itself. If the sensor were
>bad, it would show a code of a bad input, output, or power connection.
>
>It doesn't.

The P0240 -is- a downstream oxygen sensor code.

>"The P0420 code signals a low catalyst system efficiency. This code
>suggests that the oxygen levels are below the desired threshold (Bank 1),
>which most often results from problems with your car's exhaust or fuel
>systems."

The P0240 -is- a downstream oxygen sensor code.

>I'm sure it's the cat.
>I just don't want to replace the cat.

It's likely the converter, yes, and you should almost certainly replace it,
but first verify that it's not working by looking at the actual values.

Likely it's working right now but is marginal... actual measurements will
tell you for sure.

>And, get this, it passes smog without me doing anything but clearing the
>P0420 code and letting the readiness monitors (especially for the cat) set.

Do you have the smog numbers? The numbers are also an indication of how
marginal things really are.

>> Have you considered actually finding and fixing the problem instead of
>> constantly resetting the error? You're not doing your engine or your
>> gasoline bill any good this way.
>
>There is no problem other than the cat is the original 2004 and it has low
>efficiency, and, as a result, every once in a while the P0420 pops up and
>the readiness monitor for the cat takes hundreds of miles for it to set.

That sounds like a problem to me, and one that isn't that awful to fix with
a generic replacement.

[rdb]

On 23 Apr 2023, PietB <www.godfatherof.nl/@opt-in.invalid> posted some news
<news:u23t4e$3tosi$1...@dont-email.me>:

> If anything you did makes that front NOx "light off" brick get hotter or
> store more oxygen, then you'd be experiencing the effect that you've seen.

I don't know if hotter is better, but certainly the cat has to be at least
hot enough to reduce the nitrogen oxides by adding oxygen to them.

This video for my Chevy talks about catalytic converter cleaners, which, if
that works, must be doing something chemical to the platinum plated screen.
https://youtu.be/H2Xlh0V0f6c?t=50

For my Chevy, they suggest either removing the cat and soaking in detergent
for 10 hours, or pouring LiquiMoly catalytic system cleaner & driving it.

When I looked up what the LiquiMoly did though, it only says that it
prevents soot from getting into catalytic converer in the first place.
https://www.liqui-moly.com/en/catalytic-system-cleaner-p000055.html#8931

The video explains the detergent method cleans out the honeycomb screens.

That video also covers extending the oxygen sensor away from its mount but
if they're going to visually inspect all your hoses, they'll see that too.

It could be that your watery gas somehow cleaned out the screen honeycomb?

[Peter Moylan]

On 23/04/23 19:28, Bob F wrote:
>> If you have the time for your next smog, I suggest you do NOT clear the
>> codes (because then you add the second readiness monitor to the mix), but
>> that you let the drive cycle (usually around 50 miles) clear it for you.
>
> Would any electrically controlled fuel injection engine continue to
> inject fuel into a cylinder to which it had cut off spark?

It's a $200 Mitsubishi 4-cylinder econobox engine.
There's no way each cylinder is individually directly injected.

Most FI cars still add the fuel the same way the carburetor did.
It goes into the intake manifold where the next open cylinder gets it.
--
Peter Moylan

[Michael]

On Sun, 23 Apr 2023 23:00:56 +0530, mike wrote:

> You don't seem to know engines well, so allow me to explain that when the
> engine sees a misfire in 1 out of 200 revolutions (most cars), the engine
> control module permanently shuts down the spark to that cylinder (to
> protect the cat).

Does the PCM shut down the spark or the fuel to that misfiring cylinder?
--
[I filter out Google Groups posts so if I don't reply, that may be why.]

[Scott Dorsey]

In article <u23u6h$3qt5h$1...@paganini.bofh.team>, rdb <r...@usa.usa> wrote:
>
>It could be that your watery gas somehow cleaned out the screen honeycomb?

All that steam could have. But by the same token, backfiring and stammering
may have cause enough shock waves in the system to clean it out too.

[Maxmillian]

On 23 Apr 2023 18:38:03 -0000, Scott Dorsey wrote:

>>Could the water:gas mixture, somehow, have increased the cat efficiency?
>
> Certainly. All that steam in there could have cleaned the converter out.
> But it ALSO could have cleaned out the downstream O2 sensor. And it might
> have temporarily cleaned something completely unrelated too.

It could be the steam that cleaned the platinum based metal group screens.
Or maybe the fuel mixture was lean enough to heat the grids to burn soot?

>
>>Could the hundreds of code clearings, somehow, have wiped out a buffer?
>
> No.

Might be based on this which says that the efficiency is calculated over a
period of time from many measurements under many conditions.
https://www.underhoodservice.com/getting-rid-of-code-p0420-with-a-little-spring-cleaning/

"For a catalyst efficiency code like P0420 to be set, a number of
criteria must be met. For example, the oxygen or air/fuel ratio sensors
must see a reduction in efficiency of the converter. In other words, the
oxygen levels before and after the converter, they don't change or they're
not within the specified levels, well, it's going to set a code.

But it is not an automatic pass or fail. The oxygen sensors need to see
this loss in efficiency over a number of drive cycles and under certain
conditions. This is why it might take a few hours or even a few days for
the light to come back on after you clear that efficiency code, and this is
why it may take time for that code to come back.

The converter has an efficiency rating that is computed by the Engine
Management System. This number rates the amount of reduction that is
occurring in the converter and its ability to even store oxygen. But the
efficiency of the converter is tied to the fuel trim of the engine.

Most engines will minutely alter the short-term fuel trim to replenish
oxygen in the converter to add fuel or reduce the amount of fuel. This
helps to keep the converter in the correct temperature range to achieve the
most efficient operation."

>>> What this means is that the O2 sensor downstream of your converter is
>>> reading an incorrect value. This could mean your converter is bad, or
>>> maybe that the O2 sensor is bad, or maybe that the connector is bad.
>>
>>When I got the Mitsubishi Lancer 2004 for $200 it had this problem then.
>>I replaced the oxygen sensor (there appears to only be one upstream sensor)
>>and that alone fixed the problem for the first smog about 5 or 6 years ago.
>>
>>There are no oxygen sensor codes.
>>I need to repeat that because the oxygen sensor is not showing any codes.
>
> You have a downstream sensor, and you know that because you got a P0240.

I think he said a P0420 but you probably just transposed the numbers as
that's an efficiency code.

>>I repeat there are no oxygen sensor codes.
>>Therefore, I see no reason to suspect the oxygen sensor on a mere whim.
>
> The P0240 -is- a downstream oxygen sensor code.

Not really. It's a comparison of the upstream to downstream code.

>>And, get this, it passes smog without me doing anything but clearing the
>>P0420 code and letting the readiness monitors (especially for the cat) set.
>
> Do you have the smog numbers? The numbers are also an indication of how
> marginal things really are.

I'd like to see them also.

>>> Have you considered actually finding and fixing the problem instead of
>>> constantly resetting the error? You're not doing your engine or your
>>> gasoline bill any good this way.
>>
>>There is no problem other than the cat is the original 2004 and it has low
>>efficiency, and, as a result, every once in a while the P0420 pops up and
>>the readiness monitor for the cat takes hundreds of miles for it to set.
>
> That sounds like a problem to me, and one that isn't that awful to fix with
> a generic replacement.

There's nothing wrong once he clears the code. It could be he changed the
calculus for the catalytic efficiency numbers by zeroing out the codes a
lot given it stores them for at least a few days according to the article.
https://www.underhoodservice.com/getting-rid-of-code-p0420-with-a-little-spring-cleaning/

It could be that by eliminating the previous efficiency calculus, he starts
with a baseline efficiency calculus which is exactly what he has.

So there can't be a loss of efficiency if he gets to determine the current
efficiency by zeroing all the codes out a hundred times.

Clever if that trick works twice because you get to determine the baseline
efficiency, instead of letting the ECM/PCM determine its own efficiency.

[Scott Dorsey]

Maxmillian <m...@max.is.invalid> wrote:
>On 23 Apr 2023 18:38:03 -0000, Scott Dorsey wrote:
>>>Could the water:gas mixture, somehow, have increased the cat efficiency?
>>
>> Certainly. All that steam in there could have cleaned the converter out.
>> But it ALSO could have cleaned out the downstream O2 sensor. And it might
>> have temporarily cleaned something completely unrelated too.
>
>It could be the steam that cleaned the platinum based metal group screens.
>Or maybe the fuel mixture was lean enough to heat the grids to burn soot?

Yup, I will buy any one of these.

>>>Could the hundreds of code clearings, somehow, have wiped out a buffer?
>>
>> No.
>
>Might be based on this which says that the efficiency is calculated over a
>period of time from many measurements under many conditions.
>https://www.underhoodservice.com/getting-rid-of-code-p0420-with-a-little-spring-cleaning/
>
> "For a catalyst efficiency code like P0420 to be set, a number of
>criteria must be met. For example, the oxygen or air/fuel ratio sensors
>must see a reduction in efficiency of the converter. In other words, the
>oxygen levels before and after the converter, they don't change or they're
>not within the specified levels, well, it's going to set a code.
>
>But it is not an automatic pass or fail. The oxygen sensors need to see
>this loss in efficiency over a number of drive cycles and under certain
>conditions. This is why it might take a few hours or even a few days for
>the light to come back on after you clear that efficiency code, and this is
>why it may take time for that code to come back.

Right. And we don't know what the integration time is, but we can guess
at what it is by how long it was taking for the code to come back before.
That time has been exceeded now.

>There's nothing wrong once he clears the code. It could be he changed the
>calculus for the catalytic efficiency numbers by zeroing out the codes a
>lot given it stores them for at least a few days according to the article.
>https://www.underhoodservice.com/getting-rid-of-code-p0420-with-a-little-spring-cleaning/

There's nothing *to set a new code* wrong once he clears the code. That does
not mean that there is nothing wrong. You need to see the numbers in order
to know if something is wrong.

>It could be that by eliminating the previous efficiency calculus, he starts
>with a baseline efficiency calculus which is exactly what he has.
>
>So there can't be a loss of efficiency if he gets to determine the current
>efficiency by zeroing all the codes out a hundred times.
>
>Clever if that trick works twice because you get to determine the baseline
>efficiency, instead of letting the ECM/PCM determine its own efficiency.

Yes, but how long will it take to recalculate? I would not expect it to be
very long, and previous resets didn't do this.

But really, until we see actual numbers, all anyone can do is guess blindly.

[Maxmillian]

On 23 Apr 2023 20:42:44 -0000, Scott Dorsey wrote:

>> It could be the steam that cleaned the platinum based metal group screens.
>> Or maybe the fuel mixture was lean enough to heat the grids to burn soot?
>
> Yup, I will buy any one of these.

If the mixture is rich it depletes the oxygen but if it's run lean, the
oxygen is added back, so I'm leaning toward a half tank of lean fuel.

This says the efficiency calculations is not octane dependent where adding
the water maybe monetarily raised the octane rating inside the cylinder.
https://www.bridgeanalyzers.com/service-calibration/white-papers/diagnosing-fuel-control-catalytic-converter-efficiency/

This says you might be able to regenerate the oxygen to improve the
catalytic efficiency (CE) by the use of oxalic acid & citric acid.
https://ecomodder.com/forum/showthread.php/restoring-old-catalytic-converters-efficiency-cleaning-method-35264.html

[1] "Reactivation of an Aged Commercial Three-Way Catalyst by Oxalic and
Citric Acid Washing" by S.Y. Christou, H. Birgersson, J.L.G. Fierro, A.M.
Efstathiou, Environmental Science and Technology. 40 (2006) 2030-2036. The
abstract for this article states: "The efficiency of dilute oxalic and
citric acid solutions on improving the oxygen storage capacity (OSC) and
catalytic activity of a severely aged (83,000 km) commercial three-way
catalyst (TWC) has been investigated. Washing procedures applied after
optimization of experimental parameters, namely, temperature, flow-rate,
and concentration of acid solution, led to significant improvements of OSC
and catalytic activity (based on dynamometer test measurements) of the aged
TWC. The latter was made possible due to the removal of significant amounts
of various contaminants accumulated on the catalyst surface (e.g., P, S,
Pb, Ca, Zn, Si, Fe, Cu, and Ni) during driving conditions, as revealed by
Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) and X-ray
Photoelectron Spectroscopy (XPS) analyses. For the first time, it is
demonstrated that dilute oxalic acid solution significantly improves the
catalytic activity of an aged commercial TWC toward CO, CxHy, and NOx
conversions under real exhaust gas conditions (dynamometer tests) by two to
eight times in the 250−450 °C range and the OSC quantity by up to 50%.
Oxalic acid appears to be more efficient than citric acid in removing
specifically P- and S-containing compounds from the catalyst surface,
whereas citric acid in removing Pb- and Zn-containing compounds, thus
uncovering surface active catalytic sites."

>> But it is not an automatic pass or fail. The oxygen sensors need to see
>> this loss in efficiency over a number of drive cycles and under certain
>> conditions. This is why it might take a few hours or even a few days for
>> the light to come back on after you clear that efficiency code, and this is
>> why it may take time for that code to come back.
>
> Right. And we don't know what the integration time is, but we can guess
> at what it is by how long it was taking for the code to come back before.
> That time has been exceeded now.

Everything I've read says it takes a few drive cycles which can take days
but we don't really know yet how much integration time the PCM uses for CE.

The PCM could save the CE for years for all we know about how this works.

I found a lot of articles that said it takes "40 drive cycles" though.
https://www.aa1car.com/library/ic50234.htm
"Any time the MIL lamp is on, the cause should be investigated - the sooner
the better. Ignoring it will not make it go away - unless the fault does
not recur in three consecutive drive cycles that encounter the same
operating conditions, or the fault is not detected for another 40 drive
cycles. If OBD II sees no further evidence of the problem it will turn off
the MIL lamp and erase the code."

I'm not sure why it takes 40 full drive cycles, as that's something like a
few hundred days up to an entire year if you know how drive cycles work.

But when I added "40 drive cycles" to the search, I got lots of hits.
But they all seem to be a copy of the same words, so you never know.
https://www.underhoodservice.com/obd-ii-diagnostics-tips-and-tricks-to-make-the-process-easier/
https://www.tomorrowstechnician.com/the-abc-s-of-obd-ii/
http://www.totalcardiagnostics.com/support/Knowledgebase/Article/View/33/6/obd-2-and-emissions-testing
https://www.slideshare.net/gusdiag/on-board-diagnostic-ii-obd-ii

"With some exceptions, the OBD II warning lamp will also go out if a
problem does not recur after 40 drive cycles."

If one drive cycle takes days, and about 50 miles, 40 will take forever.
Maybe he cleared all that garbage when he cleared the codes >40 times?

>> There's nothing wrong once he clears the code. It could be he changed the
>> calculus for the catalytic efficiency numbers by zeroing out the codes a
>> lot given it stores them for at least a few days according to the article.
>> https://www.underhoodservice.com/getting-rid-of-code-p0420-with-a-little-spring-cleaning/
>
> There's nothing *to set a new code* wrong once he clears the code. That does
> not mean that there is nothing wrong. You need to see the numbers in order
> to know if something is wrong.

I don't think there will be any numbers for states using the OBD test only.

>> Clever if that trick works twice because you get to determine the baseline
>> efficiency, instead of letting the ECM/PCM determine its own efficiency.
>
> Yes, but how long will it take to recalculate? I would not expect it to be
> very long, and previous resets didn't do this.

I searched for details on how the catalytic efficiency (CE) is determined
but I haven't found anything other than generic percentages reported.

> But really, until we see actual numbers, all anyone can do is guess blindly.

I would like to see the numbers but alas they likely won't exist if the
smog test is just an OBD check since an OBD check doesn't measure anything.

[mike]

On 23-04-2023 19:26 Scott Dorsey <klu...@panix.com> wrote:

>>It could be that your watery gas somehow cleaned out the screen honeycomb?
>
> All that steam could have. But by the same token, backfiring and stammering
> may have cause enough shock waves in the system to clean it out too.

There was no backfiring but lots of stammering which cleared the moment I
reset the codes, so the palpable stammering was caused by shutting down the
cylinder due to non-palpable misfiring due probably to a non-stoichiometric
air:fuel ratio due to the water in the gasoline.

I went to my glovebox to get the smog report but it doesn't show any
values. It just says the following in a chart & gives certificate serials.

Air Injection System = NA
Catalyst = pass
Computers, sensors, switches & wiring = pass
Crankcase emission controls = pass
Exhaust gas recirculation (EGR) = pass
Fuel evaporation system (EVAP) = pass
Fuel metering system = pass
Liquid fuel leak check = pass
OBDII = pass
Other emission related components/systems = pass
Smoke check = pass
Turbocharger/supercharger = NA
Vacuum lines to sensors/switches = pass

I think I found out why the readiness monitors were hard to set but I'm
still researching that so I'll write that up separately for review.

[mike]

On 24-04-2023 00:31 Peter Moylan <pe...@moylan.invalid> wrote:

> It's a $200 Mitsubishi 4-cylinder econobox engine.
> There's no way each cylinder is individually directly injected.
>
> Most FI cars still add the fuel the same way the carburetor did.
> It goes into the intake manifold where the next open cylinder gets it.

You have a good idea there as I don't know what they shut down when the
engine control module sees a misfire of 1 in 200 RPMs or more.

You can shut an injector but they only inject areas and not cylinders.
You can shut down a spark, but then you have unburned fuel in the cat.

Maybe they shut down both?

[mike]

On 23-04-2023 18:38 Scott Dorsey <klu...@panix.com> wrote:

> Likely it's working right now but is marginal... actual measurements will
> tell you for sure.

I'm looking for how they electronically determine catalytic converter
efficiency to compare the old values with the new values.

Most cites are general purpose and they also say wrong things since we know
that only the NOx matters at the front of the cat, not HC or CO emissions.

This reference explains a bit of the complexity of what it takes to set the
readiness monitors where what it says is that it's not just a simple thing.
https://www.import-car.com/catalyst-efficiency-monitors-what-are-the-o2-sensors-telling-the-pcm/

"If there are any efficiency or related codes stored or even a pending
diagnostic trouble code, they can prevent a monitor from ever running or
completing."

I wonder if there is even one inefficient code stored in the 40 stored
drive cycle results that this is what is preventing the readiness monitors
from being set?

That reference also said there are other gotchas on when a readiness
monitor will be set, for example, the fuel level apparently matters.
"Be sure that you have enough fuel in the car. Some monitors, for instance
the EVAP monitor, may require the fuel level to be between 35% and 85% to
initiate the diagnostic testing."

The reference specifically calls out the problem of setting readiness
monitors when the catalytic converter efficiency is in question.
"any time you're troubleshooting a catalyst efficiency problem, it's very
important to use a scan tool that can tell you if all the readiness
monitors have run or not. If one or more monitors are not ready, the
vehicle will have to be driven under the correct conditions to make the
monitor set. Then, and only then, will you get an accurate diagnosis."

[Xeno]

On 24/4/2023 5:09 am, Michael wrote:
> On Sun, 23 Apr 2023 23:00:56 +0530, mike wrote:
>
>> You don't seem to know engines well, so allow me to explain that when the
>> engine sees a misfire in 1 out of 200 revolutions (most cars), the engine
>> control module permanently shuts down the spark to that cylinder (to
>> protect the cat).
>
> Does the PCM shut down the spark or the fuel to that misfiring cylinder?

It will definitely shut off the fuel - if nothing else. If you have fuel
but no spark you will be flooding the cat with raw fuel. That's bad.

--
Xeno


Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)

[Michael]

On Mon, 24 Apr 2023 14:10:13 +1000, Xeno wrote:

>> Does the PCM shut down the spark or the fuel to that misfiring cylinder?
>
> It will definitely shut off the fuel - if nothing else. If you have fuel
> but no spark you will be flooding the cat with raw fuel. That's bad.

I wonder what it does because it's impossible to shut off the fuel since
there is only one intake manifold and the injectors inject fuel into it
just like a carburetor would have, only a bit closer to the cylinders.

If they shut down the fuel there will ALWAYS be fuel getting into the
cylinders, but maybe the baffles are designed that one injector "mostly"
injects into one cylinder for cars that aren't direct injected (which is
most cars that are NOT direct fuel injected).

[Xeno]

Should mention, I suppose, that it only apples to sequential injection
with cylinder specific misfire monitors, V8 & V6 engines typically. Gang
fired injection systems just might not run so well with *half* the
cylinders getting no injection pulses. 😉
For the rest it's goodbye to the cat if the vehicle continues to be
driven, or it goes into some form of severe limp mode and that pretty
much forces rectification of the issue.

[Woozy Song]

Michael wrote:

> I wonder what it does because it's impossible to shut off the fuel since
> there is only one intake manifold and the injectors inject fuel into it
> just like a carburetor would have, only a bit closer to the cylinders.
>
> If they shut down the fuel there will ALWAYS be fuel getting into the
> cylinders, but maybe the baffles are designed that one injector "mostly"
> injects into one cylinder for cars that aren't direct injected (which is
> most cars that are NOT direct fuel injected).
>

About 30 years ago, you had banked injected where fuel was dumped into
the left or right side of the intake manifold. Then came sequential
injection where the injector is next to intake valve, squirting when the
valve opens. I think there would be reasonable isolation between cylinders.

[Scott Dorsey]

Xeno <xeno...@optusnet.com.au> wrote:
>On 24/4/2023 5:09 am, Michael wrote:
>> On Sun, 23 Apr 2023 23:00:56 +0530, mike wrote:
>>
>>> You don't seem to know engines well, so allow me to explain that when the
>>> engine sees a misfire in 1 out of 200 revolutions (most cars), the engine
>>> control module permanently shuts down the spark to that cylinder (to
>>> protect the cat).
>>
>> Does the PCM shut down the spark or the fuel to that misfiring cylinder?
>
>It will definitely shut off the fuel - if nothing else. If you have fuel
>but no spark you will be flooding the cat with raw fuel. That's bad.

It's bad in the sense that it will burn up the converter but... that might
be an advantage if you have a gunked-up converter. At least if it doesn't
explode.

[Frank]

On Mon, 24 Apr 2023 14:42:13 +1000, Xeno wrote:

> For the rest it's goodbye to the cat if the vehicle continues to be
> driven, or it goes into some form of severe limp mode and that pretty
> much forces rectification of the issue.

I was also wondering how the fuel could be shut off to any cylinder since
very few normal passenger car engines inject into the cylinder itself.

[Bob F]

My sienna has one injector for each cylinder. Why would that be?

[Scott Dorsey]

Your Sienna is injecting into the intake of each cylinder, so the computer
has fairly independent control over cylinders. But there is still a
very tiny amount of mixing in the manifold.

Cars that have direct injection (which include a lot of newer BMWs) inject
directly into the cylinder rather than the intake. This requires much more
rugged injectors and much more expensive ones.

[Xeno]

More accurate fuel distribution between cylinders.

____
Xeno

[Hiram T Schwantz]

On Sun, 23 Apr 2023 23:00:56 +0530, mike posted for all of us to digest...

> The question isn't about how horrible a person I am
>

Sni9pped for your pleasure!

Is that you Arlen?

--
Hiram