Having engine trouble

[2M6]

Alright, here's the deal...my '88 Fiero GT is having some problems. Recently it has had trouble with running rough. I origionally suspected fuel pump/filter was going bad. Now this morning it drove OK to work with minor spettering and backfiring. When I went to leave this evening, the car died after 1 block. I barely made it across the intersection and into a nearby parking lot where it sits now. It doesn't want to idle without opening the throttle plate. If I hold it wide open there is no change. Repeated opening/closing of the throttle plate permits the rpm to climb slightly. Once over ~2750 rpm the engine will quickly rev out and is stable anywhere above ~3250 rpm. Not exactly clutch friendly at that rpm. When below ~2750 the engine barely runs and there is a lot of popping/backfiring/smoke. I'm not certain of the color of the smoke because there are yellow lights in the parking lot. It appears to be grayish in color (read: I think it's fuel). I am in the process of converting to a 3400 but it's not nearly ready yet and the Fiero is my DD. I am now thinking the problem may be in the ignition system based on the low rpm stumble and high rpm 'smooth' running. Any help is greatly appreciated.

[robby1870]

My friends Dakota was doing that same thing when his fuel pump (electrical) went out. It wouldnt run unless you were giving it gas and would sputter every now and then when on the gas. Just a thought

[2M6]

Thanks for the info but I'm confused because the engine seems to do better above 3000 rpm. I am stumped.

[GPXSS]

I say check your timing.. My 86GT was idling very poorly (idle hunting) and wasn't driving all that great. I checked all vacuum lines and nothing I did would fix the problem. It ended up being the timing was retarded about 10º. Grab a vacuum gauge and at least check vacuum at idle.. most of the new gauges say on them what the problem is depending on the value.

It could also be the Throttle Position Sensor

Glad to see more Fiero guys coming to this board

[Anonymous]

Could also be your IAC.. clean that and your throttlebody. Helped my car which had similar symptoms. Maybe check your plugs and wires too.

[2M6]

^^^Will try that too, thanks.

[2M6]

wasn't the IAC, disassembled and cleaned, no improvement. Installing a new MAP sensor now. (keeps fingers crossed)

[2M6]

Damn! Brand new MAP sensor made the engine run worse! Just finished pulling fuel tank and testing fuel pump, it appears to be working properly. I thought the fuel pump relay was bad because it would shut off 5 sec after the ignition was switched on but later realized it was because the engine didn't fire...I am at a loss. Time to burn it down and report it stolen. Just joking, the completion of the 3400 just got bumped to the top of my to do list. Trouble is whatever is wrong at the moment will remain a problem no matter what engine is in there! Any off the wall ideas/suggestions are welcome...

[bszopi]

Could still be the TPS. I tried the "taking apart and cleaning" bit once and it didn't help one bit. Got a new TPS and it worked just fine.

[2M6]

I cleaned the IAC not the TPS. The TPS showed correct voltage when tested but the problem is somewhat intermittent so I may try a known working TPS. Thanks

[geoffinbc]

TPS will not cause that sever of a preoblem. Engine Coolant Temp sensor is what I would check. If it is reporting temps cooler than it really is it will flood the engine. Also try starting the car in clear flood mode. Put the peddle to the floor and turn the key on and start the car. If it starts and then floods out it is getting TOO much fuel. Remember to remove you foot form the WOT position when it fires.

Test it, it should read 3400ohms @ 21*C (70F) so basically room temperature.

If it is bad install a new one from GM. Jobber parts are often not correct.

[2M6]

It has the same symtoms when it actually is cold. Had problems this morning when I tried it... Going to replace the ignition module next. The tach is dropping to 0 much faster than the actual engine RPM when the problem occurs so I think the ignition module is sending a bad signal to the ECU. Funny thing is I replaced the ignition module right after I bought the car about 3 years ago but only 12,000 miles. Wish me luck.

[Fierofiend]

Have you tried unplugging the cold start injector? If its getting stuck open, it'll flood the engine.

[2M6]

Haven't tried that yet...where is the connector for it. I am starting to suspect the ECU is the problem. When I plugged the Mac Tool engine scanner into the ALDL the parameters were going crazy. The temp would read from -40 and then jump to 300! The PROM number would go from a four digit number to ****. The RPM would show 0 and then after the engine died it would show 950. My Fiero is a 5-Speed but the TCC light would come on... I am at a loss.

[Fierofiend]

no idea about the mac tool thing, never played with one of those.

The connector to the coldstart is just behind the distributor. Follow the metal line that screws into the fuel rail and it'll direct you to the injector.