Hello everyone. Need urgent help with my daily driver:
This has happened to me twice. The engine seems to work fine, but after running for a while (say 30-45 minutes at 75MPH) , and stop at a toll, the engine stalls. When I try to start it, it will backfire. I let it sit for a while and after cools down, it will start again and run fine.
I have new distributor cap, wires, rotor, pickup coil. What else can it be.

This is urgent for me. This is my transportation to work. Thanks.

Ignition module inside distributor or coil pack next to distributor.

quote Originally posted by 88FieroV8: Hello everyone. Need urgent help with my daily driver: This has happened to me twice. The engine seems to work fine, but after running for a while (say 30-45 minutes at 75MPH) , and stop at a toll, the engine stalls. When I try to start it, it will backfire. I let it sit for a while and after cools down, it will start again and run fine. I have new distributor cap, wires, rotor, pickup coil. What else can it be. This is urgent for me. This is my transportation to work. Thanks.

I had the same problem when the Ignition module was bad. In the end the car didn`t start

It could be a bad fuel pump relay combined with low oil pressure.

quote Originally posted by phonedawgz: It could be a bad fuel pump relay combined with low oil pressure.

You Sir are a thinking man's Fiero expert. I just had to say so.

Well now; since the relays on a Fiero are virtualy all the same, try swapping out the fuel relay located on the drivers side firewall and change out the oil.

In as far as the ignition module goes, I say take it to the auto parts store, have them check it at least 3 times. They like to fail when hot so make sure they test it several times. Use good quality heat sink compound, like the stuff at Radio Shack on the module when you re-install it, the module grounds through the mounting screws, make sure those are clean too.

Low oil pressure and bad fuel pump relay? I do not understand how this combination can be causing the problem. Can someone explain this to me?

When oil is warm and the car is idled the oil pressure will be lower than when cold. If it's too low it'll shut off the power to the fuel pump. Also the Fuel pump relay can have the same effect. If the oil pressure switch is bad it'll turn off the fuel pump at a higher pressure than it should.

There's more variables that need to be answered to help us help you.
When you say backfires do you mean Backfire through the intake or Popping the exhaust.
These are two very different effects for different problems.
Through the intake... Ignition is advancing too far. (module, TPS, Temp Sens)
Through the exhaust Retarding ignition, too much fuel, complete misfire. (Module, Stuck FPR or line off, Map, TPS, Temp)
Stumbling bad spot on TPS, Module loose, Arcing in Coil, bad Coil ground, Map, Vac leak, Low/intermittent fuel pressure, IAC)

Anytime you have a stumble and an exhaust pop it's due to the ignition retarding so far to try to recover it ends up burning fuel into the exhaust. This creates the pop. If the fuel pressure drops then the stumble will happen, Fuel pulses will get longer to add fuel, ignition will retard, IAC will open, and when the fuel comes back on you dump fuel in, have extra air, and a late spark and then the burn finishes after the exhaust valve opens.
If the ignition is shutting off then you get fuel in the exhaust combined with the rest of the above resulting in a larger combustion in the exhaust.

Lots of variables.
Find the testing procedures for each and every sensor. Take time to learn them. it really helps when you can run a sensor check. Get an analog and a digital meter. Learn them both. Analog meter is about the best way to see an intermittent problem in a sensor sweep.
Maybe one day I'll set up a decent Sensor test kit to add to a Community tool program. Complete with sensor emulators.

Stu

[This message has been edited by DIY_Stu (edited 03-12-2011).]

quote Originally posted by DIY_Stu: When oil is warm and the car is idled the oil pressure will be lower than when cold. If it's too low it'll shut off the power to the fuel pump. Also the Fuel pump relay can have the same effect. If the oil pressure switch is bad it'll turn off the fuel pump at a higher pressure than it should.

I used to think this, but I was told that low oil pressure won't prevent start and running.

The fuel pump relay and the oil pressure switch are wired so either can turn on the fuel pump. If both are working correctly, loss of oil pressure will not stop the engine. However if the fuel pump relay is not functioning and you are running on the oil pressure switch alone, yes then loss of oil pressure will turn off the fuel pump.

If that happens when the oil gets hot and you are idling, you would need to let the car cool, letting the oil thicken before you could restart the engine. Restarting the engine would only happen when the oil is thick enough to build up enough oil pressure by cranking the engine.

The easy check for this is to listen for the fuel pump to run 2 seconds from when you turn the key to on, but not cranking. If the fuel pump is not running when you do this you should look at your fuel pump relay.

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if the fuel pump is running for two seconds when the key is turned to on, then look elsewhere for this problem.

quote Originally posted by phonedawgz: However if the fuel pump relay is not functioning and you are running on the oil pressure switch alone, yes then loss of oil pressure will turn off the fuel pump. If that happens when the oil gets hot and you are idling, you would need to let the car cool, letting the oil thicken before you could restart the engine. Restarting the engine would only happen when the oil is thick enough to build up enough oil pressure by cranking the engine.

While technically this is true, your oil pressure would have to drop below the cut-in/cutout pressure of the switch to turn off the fuel pump, which is 4 psi. If your oil pressure gets this low when the oil is hot and you're at idle, you have other problems.

Just wondering if you had ever resolved this issue? I'm driving mine today and it's getting more mileage than usual in a day, so when I get back to town I had something like this happen without the backfire. I noticed the check engine light had been on a couple times earlier when I was climbing steep hills in 2nd gear, and then today when I was about 8 miles from town. Hit the red light in town, thought it was idling a bit low and then it just stalled (had the clutch disengaged and was sitting waiting for the light to change).

Guess I'll have to get those codes checked out and see what (if any) indicators I get from there.