I have a 1987 Pontiac Fiero Sport 2.5l

It will run perfectly fir 14 mins until the car reaches 150 degrees then just shuts off.

If i let the car sit for 12 mins exactly it will start and once again run perfect until it reaches 150 degrees

I have replaced almost all sensors on the engine, a new ECM, and a new ICM (The car has coil packs not the distributor)

The only real electrical problem iv noticed is the oil pressure gauge goes straight to 90 even when cranking

The car doesn't throw a code it just shuts off.

New parts: (Fuel pump, Fuel injector, Fuel Filter, ECM, ICM, Crankshaft position sensor, Coolant temp sensor) (theres other sensors that were replaced by the previous owner that i dont know the name of)

Theres plenty of fuel pressure the injector just stops firing

I might have missed some stuff and if anyone has any questions ill answer as quick as possible

Im really hoping someone has had this issue because i havent seen any post about this.


UPDATE: The car still shuts off with the temp sensor disconnected

But after further investigations it not only looses fuel injection the spark becomes VERY weak or completley looses it all together

(I will fire off of starting fluid but not gas) I installed a new O2 Sensor in hopes it helps the injection problem and too its credit it DID run about 2 mins longer It died 3 times but did restart before not starting all together

The car does appear too start too run mildly worse before it dies

[This message has been edited by Rune82 (edited 10-19-2024).]

The only major function change that is temperature dependent is the transition from Open Loop fueling to Closed Loop. This happens around the 150 degree range, so it might me worth looking into.

While in Open Loop, the fueling is based on tables in the ecm and not the feedback from the O2 sensor. Once up to temp, fueling starts being adjusted based on readings from the O2 sensor.

Try unplugging the O2 sensor and see if it will run past 150 degrees. If it does, there is something wrong with the sensor or wiring.

quote Originally posted by fieroguru: The only major function change that is temperature dependent is the transition from Open Loop fueling to Closed Loop. This happens around the 150 degree range, so it might me worth looking into. While in Open Loop, the fueling is based on tables in the ecm and not the feedback from the O2 sensor. Once up to temp, fueling starts being adjusted based on readings from the O2 sensor. Try unplugging the O2 sensor and see if it will run past 150 degrees. If it does, there is something wrong with the sensor or wiring.

I will give this a shot when i get home from work!

quote Originally posted by fieroguru: The only major function change that is temperature dependent is the transition from Open Loop fueling to Closed Loop. This happens around the 150 degree range, so it might me worth looking into. While in Open Loop, the fueling is based on tables in the ecm and not the feedback from the O2 sensor. Once up to temp, fueling starts being adjusted based on readings from the O2 sensor. Try unplugging the O2 sensor and see if it will run past 150 degrees. If it does, there is something wrong with the sensor or wiring.

So I did what you said it ran until exactly 150 degrees then threw code 34 and shut off
(This is the first time its thrown a code)

Progress!

Now you know it's throwing a code for the MAF sensor.

Replace the MAF sensor if it is properly hooked up properly.
Vacuum line and a three wire plug.
Inspect everything carefully.

quote Originally posted by olejoedad: Progress! Now you know it's throwing a code for the MAF sensor. Replace the MAF sensor if it is properly hooked up properly. Vacuum line and a three wire plug. Inspect everything carefully.

Can code 34 really cause it too shut off seems like a very trivial thing unless there really that much pressure

Also would just removing the vacuum line and tunning it and see if it shuts off a good test?

The map sensor seems too be rather new

quote Originally posted by Rune82: If i let the car sit for 12 mins exactly it will start and once again run perfect until it reaches 150 degrees Theres plenty of fuel pressure the injector just stops firing

So you're saying that during that 12 minute recuperation period that you still have fuel pressure. Correct?

Do you have spark? Healthy spark? Able to jump a 1/4" gap to ground spark?

quote Originally posted by olejoedad: Progress! Now you know it's throwing a code for the MAF sensor. Replace the MAF sensor if it is properly hooked up properly. Vacuum line and a three wire plug. Inspect everything carefully.

With he MAP sensor completley disconnected the car runs much better but still shuts off at 150 degrees

There is 12v at both tbi injectior fuses i dont have anyone too help me test power at the injector but ima assume its not making it there

Starting too think we have a problem with the PROM connector

[This message has been edited by Rune82 (edited 10-17-2024).]

quote Originally posted by Rune82: With he MAP sensor completely disconnected the car runs much better but still shuts off at 150 degrees There is 12v at both tbi injectior fuses i dont have anyone too help me test power at the injector but ima assume its not making it there Starting too think we have a problem with the PROM connector

If you unplug the vacuum line to the MAP sensor, then fueling will be based on 100kpa or WOT. It should cause the car to run super rich. It is interesting that it runs better like that, because it shouldn't

Still curious about the timing of the issue.

I would unplug the engine coolant temp (keep the MAP plugged in). This will tell the engine it is -40 degrees and increase fueling and cause it to run rich. The ecm will never see 150 degrees, so it would be interesting if it runs longer or shorter before shutting off.

quote Originally posted by fieroguru: If you unplug the vacuum line to the MAP sensor, then fueling will be based on 100kpa or WOT. It should cause the car to run super rich. It is interesting that it runs better like that, because it shouldn't Still curious about the timing of the issue. I would unplug the engine coolant temp (keep the MAP plugged in). This will tell the engine it is -40 degrees and increase fueling and cause it to run rich. The ecm will never see 150 degrees, so it would be interesting if it runs longer or shorter before shutting off.

Ill go do this rn

But i unplugged the MAP itself and used a vacuum plug too plug off the map line by run better i mean the iac wasnt acting up and surging like normal

Unusual problem so its time to run a full scan of the ECM that will check all parameters. It will give readings when the engine dies. Someone local probably has an OBD1 scan tool so just ask around. My wild guess is that its the ECM itself. At the time the ECM is signaled to go into closed loop the job of running the engine goes from the CALPAK to the EPROM. .

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: Unusual problem so its time to run a full scan of the ECM that will check all parameters. It will give readings when the engine dies. Someone local probably has an OBD1 scan tool so just ask around. My wild guess is that its the ECM itself. At the time the ECM is signaled to go into closed loop the job of running the engine goes from the CALPAK to the EPROM. .

I am really hoping its not that

I do wana try convincing it too run past 150 with adding some fuel in hopes it reprograms istelf into firing But if that dosent work i will be taking it too another shop

As of rn do have a couple things im gona try tomorrow

quote Originally posted by fieroguru: If you unplug the vacuum line to the MAP sensor, then fueling will be based on 100kpa or WOT. It should cause the car to run super rich. It is interesting that it runs better like that, because it shouldn't Still curious about the timing of the issue. I would unplug the engine coolant temp (keep the MAP plugged in). This will tell the engine it is -40 degrees and increase fueling and cause it to run rich. The ecm will never see 150 degrees, so it would be interesting if it runs longer or shorter before shutting off.

UPDATE: The car still shuts off with the temp sensor disconnected

But after further investigations it not only looses fuel injection the spark becomes VERY weak or completely looses it all together

Any new ideas? (I did see the ecm suggestions and i will pursue that route aswell but for rn im looking for any and all suggestions)
(I will fire off of starting fluid but not gas) I installed a new O2 Sensor in hopes it helps the injection problem and too its credit it DID run about 2 mins longer It died 3 times but did restart before not starting all together

The car does appear too start too run mildly worse before it dies

[This message has been edited by Rune82 (edited 10-19-2024).]

Well now we know if doesn't have anything to do with going into closed loop or the specific number of 150 degrees, but it does appear to be startup heat related. It starts, runs, something gets too hot, then it stalls out. Once cooled it works again.

Fuel pumps can do this with high resistance in the wiring, poor grounds, and minimal fuel in the tank. It gets too hot and just stops. Waiting 5 minutes would let you restart and continue. Topping off the tank with 50 60 degree gas from the gas station would allow it to run much, much longer as there was more cool fuel to keep it happy.

If the fuel pump relay is not working, then the car will take a long time to crank before starting (oil pressure has to build before fuel pump will be powered through the oil pressure sender). If that is the case, then as the engine heats up, the oil pressure will naturally drop, and might be dropping too low for the oil pressure sender to keep the fuel pump running.

Ignition systems can do this as well . The 87 2.5 Fiero has DIS so there will be a crankshaft position sensor, ignition module, coil pack. The tach and fuel are triggered by signals from the ignition.

If you watch the tach and wait for it to stall out again, try to see if the tach drops to zero before the engine stops spinning. If it does, it is an ignition issue. If is the fuel pump, the tach will keep working all they way down to 0 rpm.

I would pin out the wires from the fuel pump, fuel pump relay, crank sensor, ignition module, coil, and ecm checking all wires for continuity and level of resistance. Once everything is back connected, I would check resistance on all the grounds. High resistance = more heat.

quote Originally posted by fieroguru: Well now we know if doesn't have anything to do with going into closed loop or the specific number of 150 degrees, but it does appear to be startup heat related. It starts, runs, something gets too hot, then it stalls out. Once cooled it works again. Fuel pumps can do this with high resistance in the wiring, poor grounds, and minimal fuel in the tank. It gets too hot and just stops. Waiting 5 minutes would let you restart and continue. Topping off the tank with 50 60 degree gas from the gas station would allow it to run much, much longer as there was more cool fuel to keep it happy. If the fuel pump relay is not working, then the car will take a long time to crank before starting (oil pressure has to build before fuel pump will be powered through the oil pressure sender). If that is the case, then as the engine heats up, the oil pressure will naturally drop, and might be dropping too low for the oil pressure sender to keep the fuel pump running. Ignition systems can do this as well . The 87 2.5 Fiero has DIS so there will be a crankshaft position sensor, ignition module, coil pack. The tach and fuel are triggered by signals from the ignition. If you watch the tach and wait for it to stall out again, try to see if the tach drops to zero before the engine stops spinning. If it does, it is an ignition issue. If is the fuel pump, the tach will keep working all they way down to 0 rpm. I would pin out the wires from the fuel pump, fuel pump relay, crank sensor, ignition module, coil, and ecm checking all wires for continuity and level of resistance. Once everything is back connected, I would check resistance on all the grounds. High resistance = more heat.

Ill go over the wiring when i get home but fuel pump, ICm, cranshaft position sensor, ac relay, and fuelpump relay, are all brand new

As for the tach i did the test where you crank it while the symptom is there and it dosent move at al maybe a lil nudge but not much I even pulled the ICM and flipped the coil packs too see if one was bad

[This message has been edited by Rune82 (edited 10-20-2024).]

quote Originally posted by Rune82: ...fuel pump, ICm, cranshaft position sensor, ac relay, and fuelpump relay, are all brand new

Unfortunately, that's no guarantee that they're all functioning properly.

What was the brand of the fuel pump? The cheaper ones are iffy quality at best.

quote Originally posted by Rune82: Ill go over the wiring when i get home but fuel pump, ICm, cranshaft position sensor, ac relay, and fuelpump relay, are all brand new As for the tach i did the test where you crank it while the symptom is there and it dosent move at al maybe a lil nudge but not much I even pulled the ICM and flipped the coil packs too see if one was bad

You are asking for help and some of the best advice I can give you: New Part /= Good or Working Part.

I have seen countless bad parts right out of the box, especially electrical ones.

[This message has been edited by fieroguru (edited 10-20-2024).]

quote Originally posted by fieroguru: You are asking for help and some of the best advice I can give you: New Part /= Good or Working Part. I have seen countless bad parts right out of the box, especially electrical ones.

So The msg i wrote was like 5 mins before work i woulda explained more

I dont trust the parts i buy just because there new

I have 2 ecms 3 ICMs the problem occurs with all of those and as for the fuel pump its made by duralast and i installed a inline fuel pressure gauge too make sure its working properly 12-13 PSI depending on running conditions

I didnt get time too do any testing on the car today but i should have some time tomorrow and i will post a update then!

When you replaced the icm did you replace the cps? They like to work when cold but not hot.

quote Originally posted by jdv: When you replaced the icm did you replace the cps? They like to work when cold but not hot.

He said that it was replaced.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 10-21-2024).]

quote Originally posted by jdv: When you replaced the icm did you replace the cps? They like to work when cold but not hot.

I didnt end up getting too work on it today BUT

The CPS Was replaced by the previous owner my current plan is too replace it next and 2 new coil packs

My first Fiero was an '87 with a duke. I hated everything about the ignition system on that engine.

quote Originally posted by Patrick: My first Fiero was an '87 with a duke. I hated everything about the ignition system on that engine.

I Adore this car I even traded one of my collector cars for it (A 88 chevy sprint with 60k miles)

Im gona have the motor fully rebuild and i would eventually like too put a small turbo on it just too get a lil more power out of it but rn i just wana drive it

i havent even got too make it too the gas station yet

quote Originally posted by Rune82: I Adore this car I even traded one of my collector cars for it (A 88 chevy sprint with 60k miles) Im gona have the motor fully rebuild and i would eventually like too put a small turbo on it just too get a lil more power out of it but rn i just wana drive it i havent even got too make it too the gas station yet

Update! So i have the two new coil packs and the crankshaft position sensor will be here in 3 days

ill post another update tomorrow!

Usually Cherry red manifolds at idle can indicate a vacuum leak or a very lean mixture. When this happens we do a smoke test to find the leak in the intake system . It could also be a bad or clogged injector.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: Usually Cherry red manifolds at idle can indicate a vacuum leak or a very lean mixture. When this happens we do a smoke test to find the leak in the intake system . It could also be a bad or clogged injector.

Wouldnt happenen too know where one can find a vac diagram for one of these cars cause that i can tell everything is where its sapposed too be and iv always had the problem even with the old injector so ima assume the injectors fine ill check the spray pattern tomorrow


Could a bad crankshaft position sensor cause it? Idk what can cause such a lean mixture that its tryna melt my manifold

quote Originally posted by Rune82: Wouldnt happenen too know where one can find a vac diagram for one of these cars cause that i can tell everything is where its sapposed too be and iv always had the problem even with the old injector so ima assume the injectors fine ill check the spray pattern tomorrow Could a bad crankshaft position sensor cause it? Idk what can cause such a lean mixture that its tryna melt my manifold

Lots of areas could be possible trouble spots and that is why I emphasize testing and scanning. It is possible that a bad CPS could be the problem . Have you scanned the ECM as yet, done a smoke test? Not trying to be hard on you but to find problems certain test protocols are usually needed to pinpoint the problem. Working in the blind isn't the best approach .As for final suggestion just check for a bad vacuum leak or partially clogged injector. You can test the CPS with a volt/ohmeter. The procedure is explained on You Tube.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: Lots of areas could be possible trouble spots and that is why I emphasize testing and scanning. It is possible that a bad CPS could be the problem . Have you scanned the ECM as yet, done a smoke test? Not trying to be hard on you but to find problems certain test protocols are usually needed to pinpoint the problem. Working in the blind isn't the best approach .As for final suggestion just check for a bad vacuum leak or partially clogged injector. You can test the CPS with a volt/ohmeter. The procedure is explained on You Tube.

Update!!!! So I was unable too find whats causing the glowing on my own

so i called a mechanic friend of mine he comes out and calls me a complete dumbass I was reading my firing order backwards and i had all the plugs completely inverted from where there supposed too be

After running the car for 10 mins i havent noticed the LED exhaust mod showing back up so later tonight i will run the car closer too dark and post another update!!

Also wanted too say thanks too everyone who has help[ed me thus far i cant wait too drive my favorite junkyard save!