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Ignition Module Gets Better As It Warms Up? by reinhart
Started on: 01-25-2025 10:52 PM
Replies: 7 (112 views)
Last post by: armos on 01-27-2025 04:58 AM
reinhart
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Report this Post01-25-2025 10:52 PM Click Here to See the Profile for reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Weird problem.

88 GT Won't stay running when engine is cold (not ambient temp cold but engine is not up to operating temp). It will start and run for about 5 seconds then just die. I need to goose the throttle every few seconds to keep it running for about 20 minutes. After 20 minutes, car runs perfectly with good power, etc. Once up to operating temp, if I shut it off and restart it while it's still warm, it runs fine still.

I'm fairly certain it's spark related as if I try to really give it a lot of gas quickly when the engine is cold, it will backfire telling me there's unburnt fuel.

I thought it could be the pickup coil so I replaced that. No change.

So before I just start throwing parts at it, has anyone ever experienced an ignition module causing the conditions above where it will die until the engine is warm and then it runs great thereafter? All my ignition module experience is they fail at high termps not low temps.
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1985 Fiero GT
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Report this Post01-25-2025 11:16 PM Click Here to See the Profile for 1985 Fiero GTSend a Private Message to 1985 Fiero GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by reinhart:

Weird problem.

88 GT Won't stay running when engine is cold (not ambient temp cold but engine is not up to operating temp). It will start and run for about 5 seconds then just die. I need to goose the throttle every few seconds to keep it running for about 20 minutes. After 20 minutes, car runs perfectly with good power, etc. Once up to operating temp, if I shut it off and restart it while it's still warm, it runs fine still.

I'm fairly certain it's spark related as if I try to really give it a lot of gas quickly when the engine is cold, it will backfire telling me there's unburnt fuel.

I thought it could be the pickup coil so I replaced that. No change.

So before I just start throwing parts at it, has anyone ever experienced an ignition module causing the conditions above where it will die until the engine is warm and then it runs great thereafter? All my ignition module experience is they fail at high termps not low temps.


Could also be something entirely unrelated, what came to mind immediately was some bad vacuum leak, that sealed a little better as the materials expanded when warming up, could also cause the backfires. Check the EGR tube, it's connected to the exhaust, so it can get some heat through it, and being a long tube of corrugated metal, it can expand and contract pretty well with temperature.

My Fiero has a cracked EGR tube that had a super high cold idle, 2500+, and calmed down to 1000 on the dot when funny warmed up, just enough above what is supposed to be to be noticeable, but not enough to ever set a check engine light, my IAC valve and ECM were able to deal with it ok, but any more and it would have started complaining.

Only time I've ever had any form of detonation/back fire, was when my TPS was bad, it ran like garbage, and any throttle fluctuation was laggy, and large fluctuations would stall the engine or cause a backfire.
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reinhart
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Report this Post01-26-2025 06:45 AM Click Here to See the Profile for reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 1985 Fiero GT:


Could also be something entirely unrelated, what came to mind immediately was some bad vacuum leak, that sealed a little better as the materials expanded when warming up, could also cause the backfires. Check the EGR tube, it's connected to the exhaust, so it can get some heat through it, and being a long tube of corrugated metal, it can expand and contract pretty well with temperature.

My Fiero has a cracked EGR tube that had a super high cold idle, 2500+, and calmed down to 1000 on the dot when funny warmed up, just enough above what is supposed to be to be noticeable, but not enough to ever set a check engine light, my IAC valve and ECM were able to deal with it ok, but any more and it would have started complaining.

Only time I've ever had any form of detonation/back fire, was when my TPS was bad, it ran like garbage, and any throttle fluctuation was laggy, and large fluctuations would stall the engine or cause a backfire.


I imagine a vacuum leak would cause a high idle. Not seeing that. It goes up to normal 1500 on cold start then after a few second sputters down to the 400-700 range then dies.

I tried disconnecting pretty much every sensor one at a time including both the TPS and IAC and nothing changed.

[This message has been edited by reinhart (edited 01-26-2025).]

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fieroguru
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Report this Post01-26-2025 10:14 AM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sounds like a fuel issue to me as is seems to happen when running in open loop and fixes itself in closed loop.
If you can scan it, it would be interesting to see the BLM value is once warmed up.
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cliffw
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Report this Post01-26-2025 12:52 PM Click Here to See the Profile for cliffwSend a Private Message to cliffwEdit/Delete MessageReply w/QuoteDirect Link to This Post
I remember buying a new ignition module once. Not expensive. Keep your old one in case of a roadside problem.

The ignition module should be installed with die electric gel. Our Fieros are older and the gel may have deteriorated.

[This message has been edited by cliffw (edited 01-26-2025).]

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Dennis LaGrua
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Report this Post01-26-2025 03:46 PM Click Here to See the Profile for Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by cliffw:

I remember buying a new ignition module once. Not expensive. Keep your old one in case of a roadside problem.

The ignition module should be installed with die electric gel. Our Fieros are older and the gel may have deteriorated.



All grease and oils are dielectric as a non-conductor of electricity. I believe you may be referring to specific thermal grease and compounds that will provide the heat transfer to keep the module from getting too hot.

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La fiera
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Report this Post01-26-2025 04:28 PM Click Here to See the Profile for La fieraSend a Private Message to La fieraEdit/Delete MessageReply w/QuoteDirect Link to This Post
Unplug the ECM coolant sensor and see how it behaves cold and hot. How old is the Oxygen sensor? When I had the stock ECM I wired a heated 4 wire O2 sensor and it cold idled much better.
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armos
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Report this Post01-27-2025 04:58 AM Click Here to See the Profile for armosSend a Private Message to armosEdit/Delete MessageReply w/QuoteDirect Link to This Post
I see no reason to believe this is an ICM issue. The symptoms are very abnormal for that.
It's probably a fueling issue. If the ECM is confused by anything it won't fuel the engine properly.

I'd start by investigating sensors. The simplest to start with is the Coolant Temperature Sensor, which can be tested by measuring the resistance with a multimeter.

But unplugging it and seeing how the car acts as La Fiera suggested would also be a good thing to try.
The same measurements also apply to the Intake Air Temperature sensor in the air filter assembly. I don't think the ECM is as sensitive to that sensor, but it still matters. When I tested mine it was skewed to very high temperatures (which could cause a lean condition). Letting it soak in CLR restored it to normal.
A significant rip in the intake hose would bypass this sensor, which is also undesirable, but I'm more skeptical that it would cause your symptoms.

Does the Check Engine light turn on at all when you first turn on the key? It should, if not then make sure the bulb is installed.
After the engine is started the light should turn off. Are you getting any Check Engine codes?

As you may already know, you can read out the codes by jumpering the A-B terminals of the ALDL connector and turning on the key.
But if you start the engine with that same jumper in place, the check engine light will start to blink. The light will turn on when the O2 sensor is reading rich, and turn off when the O2 sensor reads lean. The O2 reading will start cycling like this when the sensor has heated up enough, which should only take 1-2 minutes in a moderate climate. Does it blink pretty steadily?
Unfortunately, this same mode also disables the ECM's ignition timing advance - the engine will be running at base distributor timing. Therefore it's more retarded than normal, so it might not behave the same as it does with the jumper removed.
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