Hi guys, I' m new in Thirdgen, I' ve posted twice in the European section. I have a very frustrating problem with my 1990 3.1 VB6 Firebird MPFI: the car runs well at cold, but stalls when hot.

Changed plug wires, distributor with ICM, replaced some vacuum lines, brake booster, spark plugs, MAP sensor, air filter, fuel filter, cleaned injectors, coolant sensor, replaced ECM, ignition coil, fixed some wires... Really, I don't know where else the problem might be.

I hear a hissing sound from the Cruise Control zone, but I can' t find where is from... Could be the PS Sensor?

Thank you for your replies guys!

 

Try to narrow down the problem.
Hook up a fuel pressure gauge and leave it connected while the car runs. Keep watching the fuel pressure when it gets hot and stalls.
After it's hot and won't run, try checking for spark.
Check the resistance across the terminals of your injectors. Check them hot, if possible. If one injector shorts out when hot, it will stop all 3 injectors in it's bank from being able to run.

 

I' ve tried yesteday, all seems to be ok... Maybe a PROM issue? I' ve noticed if I disconnect the canister purge sensor or steering pressure sensor I' ve no SES light on dash. Is it normal? I' ve a 7730 ECM

 

I'm not sure whether disconnecting those should trigger an error light or not.
I haven't worked with a 7730, but I don't think the PROM is bad. I think if the PROM is bad you'd get an error code and it would run in "limp home" mode. There should be a checksum in the ROM so the ECM will automatically detect if it's corrupt.

When the car is in a failure state, unable to start, try spraying some starting fluid or fuel into the throttle body. Does it start for a second if you do that? If it does then it's a fuel problem.

This paragraph assumes the 3.1L Firebird is wired the same as a 2.8L Fiero (which I'm most familiar with). I'm not sure if they are, but I think they are:
1) If you turn the key on (to "Run"), but don't start the engine, does the fuel pump run for 2 seconds? It should. This means that the fuel pump relay works. If it doesn't work, there is an explanation why it will still run when it's cold.

2) Try this when it's hot and won't start:If you blip the starter for a moment (not long enough to build oil pressure), does the fuel pump run again for 2 seconds? It should. It's important that you just do it quickly - we don't want the oil pressure switch to get involved. This test shows whether the ECM is receiving timing pulses from the pickup coil in the distributor. Be sure you check this when it's hot and won't start.

Do you have a way of datalogging the car with a laptop computer? If you can, maybe watching the log as it runs and then dies would reveal a problem.

 

That is normal, the ECM doesn't know that you unplugged them.

As for the hot stalling: if the injectors are the stock Multec's, even though cleaned, replace them. The coils are shorting out causing the ECM to be unable to drive them (all 6 get fired by the one driver in the ECM).

Not the PS switch. Will need to track down were the leak is from. A length of rubber hose (fuel line, coolant hose), stuck in your ear and with the other end probe around. Makes it easier to pinpoint where the hissing is coming from.

RBob.

 

Hi guys, I' ve been working on the car in the past days, still have the problem. I opened a thread in the ECM section with some Tunerpro snapshots, I' ll link it to you guys:

https://www.thirdgen.org/forums/dfi-...ird-3-1-a.html

The fuel pump seems to work correctly, it passed all tests...

Thank you!

 

Seems that the car starts to have problems when the CLOSED LOOP come in. How can I attach the Tunerpro file so you can see exactly what's going on?

 

SOLVED! The problem was in the rotor. Set the timing and now runs like a champ! Thank you guys!!

 

I have a 1991 firebird v6. I had same problems. I replaced the FUEL PRESSURE REGULATOR and fixed it.