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How to test 7MGE ign control module? Hit & miss starting problem 89 Toyota Cressida
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docsa...@yahoo.com
Sep 16, 2013, 8:05:56 PM9/16/13
to
My '89 Cressida with 7MGE has developed a problem where it takes numerous tries to start.
Crank a few - pause - crank a few - pause - crank a few - pause - crank a few - starts
Once it finally starts it runs like a clock. No problem. It got worse over the period of probably a month or so - now it does it pretty consistently when cold but will also do it after getting up to operating temp and sitting for 5 - 20 mins. If I turn it off and restart immediately it will fire up again. Sometimes it will start right up cold too.
The immediate cause is clearly no spark as per inductive timing light. Then suddenly there's spark and it runs. I've determined there's fuel - disconnected the fitting to the fuel rail when symptoms show up, wrapped it in paper towels and cranked - fuel is flowing.
So, what does this suggest? ICM going funky? What other culprits?
What's a good way to test the ICM?
Thanks for all input.
Crank a few - pause - crank a few - pause - crank a few - pause - crank a few - starts
Once it finally starts it runs like a clock. No problem. It got worse over the period of probably a month or so - now it does it pretty consistently when cold but will also do it after getting up to operating temp and sitting for 5 - 20 mins. If I turn it off and restart immediately it will fire up again. Sometimes it will start right up cold too.
The immediate cause is clearly no spark as per inductive timing light. Then suddenly there's spark and it runs. I've determined there's fuel - disconnected the fitting to the fuel rail when symptoms show up, wrapped it in paper towels and cranked - fuel is flowing.
So, what does this suggest? ICM going funky? What other culprits?
What's a good way to test the ICM?
Thanks for all input.
jim beam
Sep 16, 2013, 9:40:56 PM9/16/13
to
output. [maybe a 5th for rpm, but that depends on the unit.] once you
have those, you can use something like an led to observe whether the
unit's getting input and giving output. if it is, then you can
troubleshoot the h.t. components the old fashioned way.
[avoid touching the insides of rotor caps and rotor arms with bare hands
- salt from fingers leaves a salty conduction path.that can weaken or
rob you of spark.]
--
fact check required
Geoff Welsh
Sep 16, 2013, 11:46:16 PM9/16/13
to
docsa...@yahoo.com wrote:
> My '89 Cressida with 7MGE has developed a problem where it takes
> numerous tries to start.
>....
> My '89 Cressida with 7MGE has developed a problem where it takes
> numerous tries to start.
>
> The immediate cause is clearly no spark as per inductive timing
> light. ....
> The immediate cause is clearly no spark as per inductive timing
> What's a good way to test the ICM?
>
The ECU sends the IGT signal on the Y-G wire to the Igniter. If that's
>
pulsing, then the the wire at the negative side of the coil should be
pulsing. You may be able to see the pulsing as a flashing bulb with a
test light, but I would use a lab scope to check for a square wave.
GW
jim beam
Sep 17, 2013, 12:29:55 AM9/17/13
to
best tool to use, it's unlikely they have access to one if they're
asking the question - and inexpert use can be expensive if they get a
back-emf spike into it. i know modern scopes are supposed to be
protected, but electronics flea markets are full of scopes with a
channel out for that kind of reason.
--
fact check required
Scott Dorsey
Sep 17, 2013, 9:00:18 AM9/17/13
to
<docsa...@yahoo.com> wrote:
>My '89 Cressida with 7MGE has developed a problem where it takes numerous t=
>ries to start.
>
>Crank a few - pause - crank a few - pause - crank a few - pause - crank a f=
>ew - starts
>
>Once it finally starts it runs like a clock. No problem. It got worse over =
>the period of probably a month or so - now it does it pretty consistently w=
>hen cold but will also do it after getting up to operating temp and sitting=
> for 5 - 20 mins. If I turn it off and restart immediately it will fire up =
> suddenly there's spark and it runs. I've determined there's fuel - disconn=
>ected the fitting to the fuel rail when symptoms show up, wrapped it in pap=
flywheel pickup. If the ICM doesn't see the engine turning, it won't do
anything. If the sensor has a shorted turn it might be working okay at
high RPM but not at starting RPM.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
>My '89 Cressida with 7MGE has developed a problem where it takes numerous t=
>ries to start.
>
>Crank a few - pause - crank a few - pause - crank a few - pause - crank a f=
>ew - starts
>
>Once it finally starts it runs like a clock. No problem. It got worse over =
>the period of probably a month or so - now it does it pretty consistently w=
>hen cold but will also do it after getting up to operating temp and sitting=
> for 5 - 20 mins. If I turn it off and restart immediately it will fire up =
>again. Sometimes it will start right up cold too.
>
>The immediate cause is clearly no spark as per inductive timing light. Then=
>
> suddenly there's spark and it runs. I've determined there's fuel - disconn=
>ected the fitting to the fuel rail when symptoms show up, wrapped it in pap=
>er towels and cranked - fuel is flowing.
>
>So, what does this suggest? ICM going funky? What other culprits?
>
>What's a good way to test the ICM?
I'd look at the TDC sensor. I think on those cars there is also a second
>
>So, what does this suggest? ICM going funky? What other culprits?
>
>What's a good way to test the ICM?
flywheel pickup. If the ICM doesn't see the engine turning, it won't do
anything. If the sensor has a shorted turn it might be working okay at
high RPM but not at starting RPM.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
jim beam
Sep 17, 2013, 10:39:07 AM9/17/13
to
--
fact check required
docsa...@yahoo.com
Sep 18, 2013, 2:47:09 PM9/18/13
to
On Tuesday, September 17, 2013 9:00:18 AM UTC-4, Scott Dorsey wrote:
>
> I'd look at the TDC sensor. I think on those cars there is also a second
>
> flywheel pickup. If the ICM doesn't see the engine turning, it won't do
>
> anything. If the sensor has a shorted turn it might be working okay at
>
> high RPM but not at starting RPM.
Where is this located?
>
> I'd look at the TDC sensor. I think on those cars there is also a second
>
> flywheel pickup. If the ICM doesn't see the engine turning, it won't do
>
> anything. If the sensor has a shorted turn it might be working okay at
>
> high RPM but not at starting RPM.
jim beam
Sep 18, 2013, 11:47:23 PM9/18/13
to
--
fact check required
docsa...@yahoo.com
Sep 21, 2013, 12:23:13 AM9/21/13
to
On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
> > Where is this located?
>
> crank, cam or distributor.
I have a factory service manual, so far haven't found a mention of a TDC (top dead center) sensor. I don't think it's on the cam or crank since I don't recall ever seeing anything like a sensor on either - I'm guessing it's most likely on the distributor.
> > Where is this located?
>
> crank, cam or distributor.
> have you tested the icm yet?
What's happened since I first posted this - while getting familiarized with the wiring to the ICM, I was nosing around, grabbed and jiggled the harness connector to the coil. Now the car fires up instantly every time and runs smooth as silk as before this issue developed. I can't say for a fact that's what did it but that's the only manipulation I did and it's been running without issue since. Maybe corrosion on the connector reached a critical point and was impeding spark?
It's unclear from the previous input what I'm supposed to do to test the pulse from the ICM. Am I supposed to be able to use the inductive timing light to get a pulse from one of the ICM wires?
jim beam
Sep 21, 2013, 10:15:15 AM9/21/13
to
On 09/20/2013 09:23 PM, docsa...@yahoo.com wrote:
> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>
>>> Where is this located?
>>
>> crank, cam or distributor.
>
>
> I have a factory service manual, so far haven't found a mention of a
> TDC (top dead center) sensor. I don't think it's on the cam or crank
> since I don't recall ever seeing anything like a sensor on either -
> I'm guessing it's most likely on the distributor.
on an old distributor, each of the lobes was timed for each ignition
> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>
>>> Where is this located?
>>
>> crank, cam or distributor.
>
>
> I have a factory service manual, so far haven't found a mention of a
> TDC (top dead center) sensor. I don't think it's on the cam or crank
> since I don't recall ever seeing anything like a sensor on either -
> I'm guessing it's most likely on the distributor.
point, and that's what you're looking for here. depending on the type
of distributor it'll have a reluctor or other sensor with at least one
"pulse" generator for each of the four firing positions. [on your
4-banger.]
>
>
>> have you tested the icm yet?
>
>
> What's happened since I first posted this - while getting
> familiarized with the wiring to the ICM, I was nosing around, grabbed
> and jiggled the harness connector to the coil. Now the car fires up
> instantly every time and runs smooth as silk as before this issue
> developed. I can't say for a fact that's what did it but that's the
> only manipulation I did and it's been running without issue since.
> Maybe corrosion on the connector reached a critical point and was
> impeding spark?
are plagued by what become well known failures, are generally very
reliable. with the above caveat, it's much more likely that a problem
is a connection than it is for the electronics to actually fail.
>
> It's unclear from the previous input what I'm supposed to do to test
> the pulse from the ICM. Am I supposed to be able to use the inductive
> timing light to get a pulse from one of the ICM wires?
output, not the low voltage that would be coil input/icm output. to
test the icm, you need to identify the individual leads mentioned
previously, and use a voltage indicator of some kind, like an led.
* a classic is the honda icm or "ignitor". the ones that shipped in the
late 80's civics have a very high, near 100%, failure rate and there was
a recall. the replacement units also failed, but less frequently.
reason is, not only are they mounted in an already hot location, they
had a convoluted and poorly conducted path for its heat sink. run too
hot for too long, semiconductors fail, and that's what happens. later
models used the same ignitor, but had it directly screwed to the
distributor wall for heat sinking which was much more effective. toyota
of course, did things like mount their unit well away from heat on the
inner fender next to the ignition coil.
--
fact check required
Scott Dorsey
Sep 21, 2013, 2:52:00 PM9/21/13
to
>I have a factory service manual, so far haven't found a mention of a TDC (t=
>op dead center) sensor. I don't think it's on the cam or crank since I don'=
>t recall ever seeing anything like a sensor on either - I'm guessing it's m=
>ost likely on the distributor.=20
Toyota will call it something else. There is at least one sensor going
into the computer that tells the computer what the crankshaft position is.
If you have wires coming out of the base of the distributor, that would do
it.
TDC sensor tells the computer when to fire the plugs. The computer tells
the ignition control module when to fire the plugs. The ignition control
module puts current into the coil to fire the plugs.
All of these things fail (even the coil, and that hardly ever fails).
>
>> have you tested the icm yet?
>
>
>What's happened since I first posted this - while getting familiarized with=
> the wiring to the ICM, I was nosing around, grabbed and jiggled the harnes=
>s connector to the coil. Now the car fires up instantly every time and runs=
> smooth as silk as before this issue developed. I can't say for a fact that=
>'s what did it but that's the only manipulation I did and it's been running=
> without issue since. Maybe corrosion on the connector reached a critical p=
>oint and was impeding spark?=20
Absolutely. Now take the whole thing apart, clean it with DeOxit or
Cramolin, put a little dielectric grease on there, and put it all
back together.
While you are at it, you might as well do the same to all the other
ignition system connectors because if one is going bad, others will be
going bad in the future.
>It's unclear from the previous input what I'm supposed to do to test the pu=
>lse from the ICM. Am I supposed to be able to use the inductive timing ligh=
oscilloscope makes the job easier but a meter is fine. Skip the DMM.
>op dead center) sensor. I don't think it's on the cam or crank since I don'=
>t recall ever seeing anything like a sensor on either - I'm guessing it's m=
>ost likely on the distributor.=20
Toyota will call it something else. There is at least one sensor going
into the computer that tells the computer what the crankshaft position is.
If you have wires coming out of the base of the distributor, that would do
it.
TDC sensor tells the computer when to fire the plugs. The computer tells
the ignition control module when to fire the plugs. The ignition control
module puts current into the coil to fire the plugs.
All of these things fail (even the coil, and that hardly ever fails).
>
>> have you tested the icm yet?
>
>
> the wiring to the ICM, I was nosing around, grabbed and jiggled the harnes=
>s connector to the coil. Now the car fires up instantly every time and runs=
> smooth as silk as before this issue developed. I can't say for a fact that=
>'s what did it but that's the only manipulation I did and it's been running=
> without issue since. Maybe corrosion on the connector reached a critical p=
>oint and was impeding spark?=20
Absolutely. Now take the whole thing apart, clean it with DeOxit or
Cramolin, put a little dielectric grease on there, and put it all
back together.
While you are at it, you might as well do the same to all the other
ignition system connectors because if one is going bad, others will be
going bad in the future.
>It's unclear from the previous input what I'm supposed to do to test the pu=
>lse from the ICM. Am I supposed to be able to use the inductive timing ligh=
>t to get a pulse from one of the ICM wires?
Nope, but you should be able to see it on an analogue voltmeter. An
oscilloscope makes the job easier but a meter is fine. Skip the DMM.
Nate Nagel
Sep 21, 2013, 7:54:58 PM9/21/13
to
every accessable connector under the hood, ignition/FI related or no.
nate
--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel
Nate Nagel
Sep 21, 2013, 7:58:15 PM9/21/13
to
On 09/21/2013 10:15 AM, jim beam wrote:
> On 09/20/2013 09:23 PM, docsa...@yahoo.com wrote:
>> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>>
>>>> Where is this located?
>>>
>>> crank, cam or distributor.
>>
>>
>> I have a factory service manual, so far haven't found a mention of a
>> TDC (top dead center) sensor. I don't think it's on the cam or crank
>> since I don't recall ever seeing anything like a sensor on either -
>> I'm guessing it's most likely on the distributor.
>
> on an old distributor, each of the lobes was timed for each ignition
> point, and that's what you're looking for here. depending on the type
> of distributor it'll have a reluctor or other sensor with at least one
> "pulse" generator for each of the four firing positions. [on your
> 4-banger.]
Cressida is an inline six, if I'm not mistaken (related to if not the
> On 09/20/2013 09:23 PM, docsa...@yahoo.com wrote:
>> On Wednesday, September 18, 2013 11:47:23 PM UTC-4, jim beam wrote:
>>
>>>> Where is this located?
>>>
>>> crank, cam or distributor.
>>
>>
>> I have a factory service manual, so far haven't found a mention of a
>> TDC (top dead center) sensor. I don't think it's on the cam or crank
>> since I don't recall ever seeing anything like a sensor on either -
>> I'm guessing it's most likely on the distributor.
>
> on an old distributor, each of the lobes was timed for each ignition
> point, and that's what you're looking for here. depending on the type
> of distributor it'll have a reluctor or other sensor with at least one
> "pulse" generator for each of the four firing positions. [on your
> 4-banger.]
same as a contemporary non-turbo Supra) Definitely worth fixing as that
is a classic of quasi-modern engines and "they don't make 'em like that
anymore" (and that's a bad thing.)
that said, I haven't a clue where the appropriate sensor is on that vehicle.
Geoff Welsh
Sep 21, 2013, 9:25:26 PM9/21/13
to
had three pickup coils inside the distributor called NE, G1, and G2. If
the ECU likes what it sees, from those three, it sends the IGT signal to
the igniter over-and-over again, which grounds the coil over-and-over
again producing spark in the secondary system over-and-over again.
GW
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