i have a 1991 z28 305 tpi it runs great about 80% of the time however occaisonally it starts to run poor. it feels like the car is running out of gas it keeps hurling over as if it is not getting fuel, however if you floor it, the cars does not surge or anything. this didn't start happening until one day my wife ran the car out of fuel when it starts running poor about 25% of the time the check engine light comes the comes out as a rich exhaust trouble code. i have replaced the throttle position sensor and the iac sensor with no improvement also checked vacuum lines and didn't see anything out of the ordinary. one last thing if you turn the car of then on again it seems to go away. any suggestions

 

Change your fuel filter....that might help however the pumps need fuel without it they can either be damaged or ruined all together. I suspect that your wife damaged the pump when she ran it out of gas.

 

i did change the fuel filter and it didnt help you think it is the fuel pump?

 

that'd be my guess, if they are in good shape you can run them out of fuel once without much issue. But if the pump has taken some relatively hard wear then yeah its probably the pump all it takes is once.

 

that was my first thought but when the check engine light comes on the car runs fine again until the check engine light goes of then it runs poor again it seemed to me it might be a sensor.

 

Thats another very distinct possibility. Sensors are usually cheap and easy so that is a good place to start.

 

How old is the pump? You should try to make a point of not running the car with less than a quarter tank of fuel for two reasons. 1 the gas in the tank helps to cool the pump and the hotter it runs the shorter its life and 2 all the crap and condensation that accumulates in the tank gets sucked into the sock when you run the tank that low. Its possible the pump is starting to fail causing a lean condition that the 'puter tries to compensate for by dumping more fuel into the motor triggering the o2 to read rich. It runs better when the light is on because you've gone open loop which is a rich condition for the safety of the motor. I would get the car scanned with a good (snap on etc) scanner that you can drive the car and monitor what everything is doing. This might cost you some money but its cheaper than guessing and replacing stuff for nothing. That gets expensive. You will have a code stored in there telling you why the ses light has been coming on. Has the sound of the fuel pump changed at all?

 

Don't know if it is relevant, but had the same problem with my blazer, and it was the ignition switch in the column.

 

I just replaced my wife's ignition switch in her Rav4 two days ago. Once running the car usually continues to run if its the ignition switch. However electrical items like the radio, wipers, etc sometimse will come on at strange times. On my wife's car every light onthe dash came on for about 15 mins thats when I decided that it probably was the switch. So far so good :x:

 

I also did it on my probe gt. It would run, but backfire and cough, and sputter. I would have to turn it off and on, and it would be fine. Sometimes I could do it without shutting the engine off
! I would bet that this is his problem.

 

as a guess the fuel pump is the original so 1991 car has around 70k miles and is original. i just had a chevy dealership replace the ignition key cylinder and the security system because the car would not start all the time ($1200)and that hurt alot. what you are saying about the fuel pump makes since does the code scanner work on 1991 i thought that it only worked on obd2 cars thanks

 

Heres exactly what I would do....

1. Replace the fuel pump relay... doesn't sound like a bad pump.
2. Take it back to the chevy dealership because there is something wrong with the ignition switch.