My 87 Fiero shuts off at 150 degrees (Page 1/4)
Rune82 OCT 16, 02:48 AM
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).]

fieroguru OCT 16, 06:54 AM
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.
Rune82 OCT 16, 02:24 PM

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!
Rune82 OCT 17, 04:26 PM

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)
olejoedad OCT 17, 04:39 PM
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.
Rune82 OCT 17, 04:56 PM

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
Patrick OCT 17, 05:40 PM

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?
Rune82 OCT 17, 06:07 PM

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).]

Rune82 OCT 17, 06:20 PM

quote
Originally posted by Patrick:

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?




Yes it still has perfect spark if you dump gas down the intake it starts and dies

and fuel pressure is perfect (11 - 12 psi im using a mechanical inline gauge)

(fuel pump and filter are brand new because i thought the same thing)

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

fieroguru OCT 17, 08:04 PM

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.