3000 RPM stumble on 93 RX7
Mark Wetzel
during light throttle?
Thanks in advance.
MAR34807
has been found. People have tried additional ground wires, reprogramming the
ecu, and all manner of other thingsto control it (additional fuel in the maps,
etc).
If you disconnect your battery for 15 min and then reconnect it, you will find
the ecu again has to relearn it's program. You will have no stumbling until a
little later when it comes back.
One theory has it that the injectors go lean just before the crossover to the
main turbo and that causes a momentary hesitation. Mazda has not said anything
about it, but there are many different pn's for later model ecu's that may help
if you got over a $1000 to spend to get one. Try and approach it as an
emissions problems with the dealer and see if they will ante up a new ecu.
Mazda needs to address this problem with a service bulletin, but that would
cost $. I bet the 98 and 99 models in Japan don't do it.
Recent discussion follows:
Subject: (rx7)[3] 3K hesitation info-new theory?
Another data point...
It looks like removing the DTCS does not make the hesitation go away.
Does anyone know if the manifold pressure sensor changed part numbers
over the years, and if so are the later cars are less likely to have the
hesitation? Perhaps Mazda found a faster sensor over the years and
quietly fixed this problem.
Or could the sensor be replaced with a faster but functionally similar
replacement? Does anyone have any info on how we might select such a
replacement? For example, what is the sensor's output signal and is it
"standard"?
So I am now looking for reports of:
- - Changes in the manifold pressure sensor number
- - Reports of '95 model cars with the hesitation
- - Considerations for replacing the stock sensor with another model
- -Max
My double throttle is completely removed (even the valves). I had the
hesitation before and after the conversion. Ground wires did not help
either. The hesitation only occurs between 0 and 4psi of boost. I am
convinced there is a program error in the ecu. You can post this to the
list if you would like.
I just read on page F-137 of the 1993 Workshop Manual:
>>start>>
DOUBLE THROTTLE CONTROL SYSTEM
DESCRIPTION
The response delay of the pressure sensor followed mounted by rapid
acceleration temporarily causes a lean fuel mixture. The double throttle
control system prevents hesitation caused by this lean fuel mixture by
slightly delaying the opening of the double throttle valve after the
secondary throttle valve.
The double throttle valve is controlled by the ECU through the solenoid
valve.
(diagram showing that the solenoid is activated (thus closing the double
throttle) by the conditions labeled "IDLE ZONE" or "COOLANT TEMP BELOW
80C [176F] | START-UP ACCELERATION (AT)")
OPERATION
When one or more of the above conditions are met, the ECU turns the
solenoid valve ON, applies vacuum to the actuator (double throttle
control), and closes the double throttle valve.
<<end<<
This sounds a lot like it might be related to the 3K hesitation that
plagues these cars. My car goes lean very clearly when the hesitation
occurs. And it seems to be the worst under light boost (~2 psi). Still,
it is not very clear what is being said here, so I don't know quite how
it relates.
It sounds like maybe the pressure sensor is slow to react. It would be
interesting to see how quickly it reacts compared to a mechanical boost
gauge. Perhaps an analog volt meter placed next to the boost gauge could
reveal a delay. Some ways to improve that situation could include using
a shorter, stiffer hose to connect it to the manifold. And perhaps the
gas filter in that line clogs over time and causes the problem to get
worse with age. Replacing the filter might help. Or maybe the sensor
gets slower with age, replacing it might be expensive, but you bet I'd
pay if it solved the problem. Perhaps the sensors could be swapped on
two cars to see if the problem follows the sensor or stays with the host
car.
I would be interested to hear if or how bad people who have removed the
DTCS system experience the 3K hesitation. If removing it eliminates the
hesitation that would be great. I may even try wiring mine open to see
what happens.
However, since the system is there in the first place, the ideal
solution may be to get it back into top working shape. A new check
valve, actuator, or simply cleaning the mechanism might be the way. It
sort of feels like it may just be opening a little too late-perhaps a
lag caused buildup or something.
Does anyone have any related experiences or information they would like
to relay? It would be a great service to the [3] owners community if we
could find a real solution to this problem. I've got all the grounds and
they don't help-it seems disconnecting the battery to add the grounds
may give this false impression.
AND
Subject: Re: (rx7)[3] 3K hesitation info-new theory?
Things that don't seem to fix the hesitation:
* removing the DTCS
* buying a later model ECU/car
* installing new engine grounds
Things it might be:
* fuel pressure problems
* slow manifold pressure sender or plugged filter in the MAP sensor line
I am now looking looking for:
- - people who fixed their hesitation with fuel system maintenance or
upgrades
- - manifold pressure sensor information
- - people who experienced this problem in factory-new cars
It seems like the cause of the hesitation might be a number of little
problems. That would explain how this problem made it into production
cars. A lot of things do seem to happen around this RPM range --
secondary injectors come online, fuel pump gets full voltage, double
throttle plates open, air pump disengages, etc. And there has been no
definitive fix discovered yet.
Still looking...
efin...@my-deja.com
it or not.
~Efini
In article <s21l85...@corp.supernews.com>,
Sent via Deja.com http://www.deja.com/
Before you buy.
iamthegreatcornholio
sensor. Wouldn't be a stretch on a car that runs rich as hell when it's
cold. There are many theories out there on this, such as poor grounding
etc., but it would be interesting to see if the problem goes immediately
away with a new sensor. Keeping that one clean for any length of time though
would be a feat.
Tom L. Davis <m...@home1.com> wrote in message
news:me-051199...@c190355-a.croltn1.tx.home.com...
> Oh, you'll know it if it happens. Worst case it feels like you hit a kill
> switch or jabbed the brakes. This is really great if you're drinking
> coffee on the way to work. On mine, it happens as the engine is
> transitioning from 'cold' to 'wramed-up' operation (about 1 to 2 miles in
> city traffic from cold start up).
>
> Too bad we can't file a class action law suit against Mazda for this peice
> of shitty engineering.
>
> Tom
>
> --
> Use this to reply: toml...@home.com
Tom L. Davis
Andrew
and for the first few times after that to gradually increase the revs past
3000 to about 4000 (rather than stomping on the accelerator), the hesitation
doesn't happen. On the other hand, accelerating above 3000 without warming
up well is like hitting a patch of treacle on the road.
Andrew
iamthegreatcornholio <iamthegrea...@erols.com> wrote in message
news:80042u$p70$1...@autumn.news.rcn.net...
> If it happens when transitioning from cold to warm, I'd suspect the oxygen
> sensor. Wouldn't be a stretch on a car that runs rich as hell when it's
> cold. There are many theories out there on this, such as poor grounding
> etc., but it would be interesting to see if the problem goes immediately
> away with a new sensor. Keeping that one clean for any length of time
though
> would be a feat.
>
> Tom L. Davis <m...@home1.com> wrote in message
> news:me-051199...@c190355-a.croltn1.tx.home.com...
Chris Nielsen
iamthegreatcornholio wrote in message <80042u$p70$1...@autumn.news.rcn.net>...
>If it happens when transitioning from cold to warm, I'd suspect the oxygen
>sensor. Wouldn't be a stretch on a car that runs rich as hell when it's
>cold. There are many theories out there on this, such as poor grounding
>etc., but it would be interesting to see if the problem goes immediately
>away with a new sensor. Keeping that one clean for any length of time
though
>would be a feat.
If it is the O2 sensor, can you unplug them on this model? I assume that
the computer would flag the disconnected O2 sensor with an error code, and
switch to alternate sensors - i.e. MAP + AFM instead of MAP+AFM+O2.
I know on my 2nd gen the O2 sensor seems to do bugger all...
This might reveal if the O2 sensor is rooted..
Later
Chris
her...@pop.phnx.uswest.net
>
> Too bad we can't file a class action law suit against Mazda for this peice
> of shitty engineering.
Now wouldn't that be a *great* encouragement for them to
bring rotaries back to the market?
Tim Herbst
85 GSL-SE unmodified @62k
94 VR Base/Pettitized
her...@pop.phnx.uswest.net
>
> I find that if I let the car get good and warm before going above 3000 rpm,
> and for the first few times after that to gradually increase the revs past
> 3000 to about 4000 (rather than stomping on the accelerator), the hesitation
> doesn't happen. On the other hand, accelerating above 3000 without warming
> up well is like hitting a patch of treacle on the road.
I always thought taking a cold rotary above 3000 was more
like tasting yesterday's warm potato salad.
iamthegreatcornholio
loop, running off maps of air volume, throttle position and temperature
info, and almost definitely overrich. I haven't experimented much with the
sensor, but hope to soon. It is such an important part of the computer's
mixture information, at least from a performance standpoint. My main
curiosity with this car would be to track conditions and at intervals,
measure it, log the measurements, pull it, and record observations made
about its condition. Not too scientific, but I really think looking at this
component's performance would be helpful.
Chris Nielsen <chr...@startrek.gen.nz> wrote in message
news:94186996...@ham.ihug.co.nz...
> >> Too bad we can't file a class action law suit against Mazda for this
> peice
> >> of shitty engineering.
> >>
MAR34807
I had the same problem and it was equally resistant to all the
well-known cures. Turned out it was a cracked outlet nozzle on the fuel
pump which lives inside the fuel tank. How it got cracked is a whole
'nother story. But suffice to say that when the seocndary injectors
come in at 3,ooo rpm, the fuel pump needs to make a whole lot of
pressure. If it doesn't -- there's your hesitation. If I drove mine
with about 2-3 psi of boost, it would sometimes buck like an angry
bronc. If any of this sounds familiar, have your fuel pressure checked
UNDER LOAD -- like on a dyno.
iamthegreatcornholio
MAR34807 <mar3...@aol.com> wrote in message
news:19991112163904...@ngol05.aol.com...
MAR34807
infamous 3rd gen 3000 rpm hesitation. NOTE: it appearns NONE of the automatic
tranny models have it (diff ECU?). So lets take our own. Give year, model,
miles, mods, type tranny, what you did to (try) get rid of it, anything else
you can think of.
FWIW, one of the respondents on the other list said "check your ground and/or
add another ground between the downpipe with the oxygen senson and the body
frame ground. This is the only one I have not done. So here is my info:
94 PEP 5 speed, 51000 miles, all the battery grounds, new battery, cleaned all
grounds, no other problems whatsoever up to now except this. Original fuel
filter, have not cleaned injectors.
Mike Gray
> Original fuel
> filter, have not cleaned injectors.
The folks at Pettit are very big on frequent fuel filter changes, saying they clog
easily.
My 3gen had the infamous stumble, virtually all of which disappeared with the
Pettit intake/exhaust/pulley kit mod. At the same time, they added an additional
ground cable from batt'y to body.
I have noted that I get all kinds of wierd problems when the battery starts to go
soft, long before "normal" symptoms such as slow cranking and dim headlights on
idle.
The Japs certainly love to copy the Brits - maybe they stole some secret Lucas
documents.
regards
m
efin...@my-deja.com
experienced 3k stumble ever.(owned car for about 5 months) Battery looks
pretty new and clean. Just a lot of backfire from running rich. Maybe a
bad O2 sensor??
In article <19991113181414...@ngol03.aol.com>,
> grounds, no other problems whatsoever up to now except this. Original
fuel
> filter, have not cleaned injectors.
>
Dennis
Fuel filter was changed. I had the hesitation, but I haven't
experienced it since the cat back, downpipe, and fuel filter. The vacuum lines
did improve it but didn't cure it. 5spd. 39K miles
MAR34807 <mar3...@aol.com> wrote:
> On the big rx7 list they are taking a poll of how many 3 rd gens have the
> infamous 3rd gen 3000 rpm hesitation. NOTE: it appearns NONE of the automatic
> tranny models have it (diff ECU?). So lets take our own. Give year, model,
> miles, mods, type tranny, what you did to (try) get rid of it, anything else
> you can think of.
> FWIW, one of the respondents on the other list said "check your ground and/or
> add another ground between the downpipe with the oxygen senson and the body
> frame ground. This is the only one I have not done. So here is my info:
> 94 PEP 5 speed, 51000 miles, all the battery grounds, new battery, cleaned all
> grounds, no other problems whatsoever up to now except this. Original fuel
> filter, have not cleaned injectors.
--
If there is a NOSPAM in my address remove it
to email me.
Mike Gray
> 1993 Base 46K miles 5-speed. modified intake, exhaust, downpipe. Never
> experienced 3k stumble ever.(owned car for about 5 months) Battery looks
> pretty new and clean. Just a lot of backfire from running rich. Maybe a
> bad O2 sensor??
I believe all intake/exhaust mod'd 3gens backfire. SWAG, the improved
flow/extraction beats the fuel metering on overrun.
regards
m
Andrew
in first, but it was only after adding the exhaust that the car would
backfire from time to time. I guess the airflow is increased to the point
where the computer just dumps as much fuel as possible in there. I've
noticed some sooty deposits around the exhaust tip also, more than before.
Andrew
Mike Gray <omg...@worldnet.att.net> wrote in message
news:38303029...@worldnet.att.net...
efin...@my-deja.com
intake/downpipe/exhaust. My car is an early build. 2/92. I heard the ECU
in early 93s tend to run more fuel then later ones. Is this true?
~Efini
In article <38303029...@worldnet.att.net>,
omg...@worldnet.att.net wrote:
> efin...@my-deja.com wrote:
>
> > 1993 Base 46K miles 5-speed. modified intake, exhaust, downpipe.
Never
> > experienced 3k stumble ever.(owned car for about 5 months) Battery
looks
> > pretty new and clean. Just a lot of backfire from running rich.
Maybe a
> > bad O2 sensor??
>
> I believe all intake/exhaust mod'd 3gens backfire. SWAG, the improved
> flow/extraction beats the fuel metering on overrun.
>
> regards
> m
>
>
Chris
Andrew wrote in message <4P4Y3.14851$YI2.7...@typ11.nn.bcandid.com>...
>I'd agree. I have a '93 with downpipe and PFS exhaust. The downpipe went
>in first, but it was only after adding the exhaust that the car would
>backfire from time to time. I guess the airflow is increased to the point
>where the computer just dumps as much fuel as possible in there. I've
>noticed some sooty deposits around the exhaust tip also, more than before.
>
>Andrew
Hang on a sec, something isn't right here... when my exhaust mods made my
car start backfiring, I was stoked :-)
later
chris
Mike Gray
> My friend's Automatic 93 doesn't backfire w/ identical
> intake/downpipe/exhaust. My car is an early build. 2/92. I heard the ECU
> in early 93s tend to run more fuel then later ones. Is this true?
Don't know. Mine's a '94. Automatics almost certainly have a different fuel
metering profile, though. (?)
and as Andrew notes, there is that black soot where I think a nice grey film
should be. Pettit says it's normal, but it definitely means too much C and
not enough O2, hence my guess that it's allowing a too-rich fuel/air ratio
on overrun.
But it runs like stink and the backfire only bothers the bluehairs.
regards
m
Jerry Logsdon
> On the big rx7 list they are taking a poll of how many 3 rd gens have the
> infamous 3rd gen 3000 rpm hesitation. NOTE: it appearns NONE of the
automatic
> tranny models have it (diff ECU?). So lets take our own. Give year, model,
> miles, mods, type tranny, what you did to (try) get rid of it, anything
else
> you can think of.
> FWIW, one of the respondents on the other list said "check your ground
and/or
> add another ground between the downpipe with the oxygen senson and the
body
> frame ground. This is the only one I have not done. So here is my info:
> 94 PEP 5 speed, 51000 miles, all the battery grounds, new battery, cleaned
all
> grounds, no other problems whatsoever up to now except this. Original fuel
> filter, have not cleaned injectors.
94 5spd, PFS cat back, silicon lines, newish fuel filter, 35K miles. My car
stumbles quite often when cold and even occasionally when hot. I added a
ground between the engine block and body which seemed to help, but maybe
just because I wanted it to. My car defineatley runs rich, as the sooty
exhaust tip shows, but it was my understanding that they did that on purpose
to keep the engine from ever knocking or overheating. My gut feeling is the
place to add an additional ground wire would be directly to where the
secondary injectors are grounded, but I haven't dug thru my service manual
to see where that is.
MAR34807
>The rotary NG came with an idea that the 3K hesitation is caused by a lack
>of fuel to feed the secondaries. The fuel pump cannot keep up with instant
>demand when cold/low system voltage and takes a bit of time to compensate.
>
>Any ideas if this might be reasonable?
So, that would lead us to ask the question: Has anyone who has replaced
the stock fuel pump with a bigger/better pump noticed that their 3k
hesitation went away?
Tonight I replaced the engine->firewall ground with the updated
ground wire from Mazda. It basically is just a ground strap that
eliminates the original snap on connection. I had already cleaned
the old connection as well as cleaning the other ground points and
adding a battery->chassis ground... didn't help any. I'll let you
know if this does anything.
Also, I love my M2 modified ECU... but it didn't help the
3k hesitation any.
MAR34807
From: Dun...@aol.com
Subject: Re: (rx7) (3) 3k Hesitation Solved
I have the fuel pump upgrade from RP, and I never noticed a difference
Doug
MAR34807
List:
A persistent case of 3k hesitation that does not respond to the
well-documented fixes involving optimizing electrical
grounds/battery/alternator may well be fuel related. It happened to me.
The secondary injectors come on stream at 3k rpm. If the fuel pump is
not making sufficient pressure (more than 50 psi -- !) you will get a
reaction that can seem more like a saddle bronc than a high performance
automobile.
The way to know for sure is to have your favorite dyno-equipped RX-7
shop test the fuel pressure under load. Testing the pressure with the
engine not driving the rear wheels may not give you an accurate reading
on what your fuel system is -- or isn't -- doing.
Dave Booth
MAR34807
From: David Disney <dis...@icx.net>
Subject: Re: (rx7) (3) 3K Hesitation - Additional Information
At 10:10 AM 11/17/99 -0700, you wrote:
>Since this has been a continuing area of interest on this list, I thought
>I'd share my experience (fix and re-fix) with the 3K engine gremlin.
>
>I purchased my car 2.5 years ago. After driving it for only a couple of
>days I noticed the peculiar hesitation at 3K rpm. List wisdom at the time
>was to solve the problem by installing an additional grounding strap, which
>I did. My 3K hesitation completely disappeared as a result.
>
>The car ran fine until the last few weeks, when I noticed that my 3K
>hesitation had returned. I first assumed that it might have something to
>do with the cooler air and my cars' state of tune (generally very good, but
>it's time to do some routine maintenance). Anyway, last weekend, I noticed
>that my car would crank slowly on occasion, which suggested that the
>battery was dying (original battery in a '94). I replaced the battery
>yesterday and viola -- no more 3K hesitation.
>
>One of the interesting things here is that the 3K hesitation showed up
>before I had any other indication that the battery was failing. It just
>makes me wonder if some of the people who have been fighting this problem,
>but are unable to solve it with an additional engine ground might have weak
>batteries -- but not so weak that any other problems/symptoms are evident.
Here's my data point:
Additional Ground from Battery to Chassis
New (and well cleaned) ground from manifold to firewall.
Cleaned engine block ground
Cleaned exhaust system ground
Cleaned ECU ground
New Mazda O2 sensor (ouch! wish I had bought a Bosche)
New Optima red-top battery
I still have the 3K hesitation. I only see it if I'm making
between one to three pounds of boost. It appears in
all gears at 3K as long as the throttle usage is light and
boost is as mentioned above.
It does not appear if the car is reading vacuum (ie. extremely
light throttle use).
My double throttle system is disabled (uh, actually the
solenoid broke and I capped the vac line off until I
get around to replacing the solenoid). I had the
3K problem with and without the DT working.
My air/fuel gauge goes completely lean during the
hesitation (which only lasts a split second).
Someone mentioned that disconnecting the O2 sensor
cured his problem. This isn't something I would want
to do as a permanent fix, but it makes me wonder...
Is the ECU seeing the lean condition and causing
the hiccup as it tried to correct for it? Or, is the lean
condition a result of the hiccup? I would guess that
the latter possibility is the case. Does anyone
with a heated O2 sensor have the problem?
Also, I installed a new Bosche O2 sensor in a
friend's '93. He also has an a/f meter that I
installed... and it goes full lean during the
3K hesitation.
Someone else said that replacing the alternator
cured their problem. That isn't something I'm
prepared to try yet. I am beginning to wonder
if some people _think_ that they cured it
(new alternator, battery, etc.) when they
actually just reset the ECU by depriving it
of power... this cures my hesitation for
one drive. When I drive the car again
the hesitation is back.
Maybe we should contact someone at Mazda
Corporate and tell them that we are a fairly
large group of owners and that we would
appreciate it if they could point us in the
right direction. Some engineer at Mazda
HAS to know what the problem is... and it
obviously ain't just grounding problems. I
don't mean to threaten them or ask them
to send us all new parts... just let us know
what the cause is and how we might fix
it ourselves. There is a Mazda bulletin of
some sort floating around that instructs
them to add/clean the grounds, but we
all know that doesn't usually work.
- Dave Disney
http://rx7.voodoobox.net
MAR34807
From: Fred <ca...@paradsgn.com>
Subject: (rx7) 3K hesitation
Interesting David but the new battery (730 amp even) along with several
additional ground straps did NOT solve my 3k hesitation. And I guess
that's the frustration in all of this. This problem is so very elusive
because the cause has yet to be defined. Plenty of theories that sound
very plausible though.
>One of the interesting things here is that the 3K hesitation showed up
>efore I had any other indication that the battery was failing. It just
>akes me wonder if some of the people who have been fighting this problem,
>ut are unable to solve it with an additional engine ground might have weak
MAR34807
From: Fred <ca...@paradsgn.com>
Subject: (rx7) 3K Hesitation definition
Maybe we should all agree for consistancy that the classic 3k hesitation is
hesitation around 3k under light load and with a fully warmed up engine.
That means it takes just the right load to induce it. It therefore doesn't
occur all the time. I don't think any of us would be upset if it only did
it during warm up or with a cold engine would we?
>I have the same problem with the hesitation. But only when on light
>throttle. I notice at the 3k hesitation point my car also starts to run
>rich. Like it changes the fuel map. I was just wondering could the
>hesitation just be a sudden shot of fuel going into the motor and thus
>causing the hesitation? Just a thought.
MAR34807
From: Kyle Johnson <kjoh...@conceptserv.com>
Subject: (rx7) [3] fuel pump vs 3K hesitation
>So, that would lead us to ask the question: Has anyone who has replaced
>the stock fuel pump with a bigger/better pump noticed that their 3k
>hesitation went away?
I have replaced the stock pump with the upgrade sold by Rotary Performance
along with a tunable boost sensitive pressure regulator. No change to report
in the 0-2psi throttle position / 3000 rpm hesitation effect. I did not
install these items in the hopes that it would cure this particular problem,
but I was slightly disappointed to be unsurprised that they did not.
Kyle
'93 Silver Touring Much Modded
Fabian Okonski
i'm glad this topic has come up again....i am at my wits end with this
problem. the fellow who works on my car (rotorsport, campbell, CA)
thinks the only real solution is to upgrade the cpu to a 94 or newer
version. we've done most of the half assed fixes without success. this
is my only real gripe with the car....but it really irks me. unlike
some others on the list, my car does it most of the time, and is worst
under heavy loading, to the point where it almost seems to stall
momentarily.
i like the idea of trying to get mazda engineering to help us. it is
absurd that such a prominent problem hasn't been worked out.
fabian
--
_____________________________________
ABSURD DILEMMA #93
Would you rather be sentenced to a permanent ice cream headache or a
never ending lecture entitled "Fabio: Cross cultural perspectives"
_____________________________________