I'm doing some work on a '91 Z28 305 TPI. I'm having some trouble getting the car to run smoothly and i'm somehow losing power when i hit the pedal.

I did some updates on my findings, please see the below post:

 

disregard.

see next post-->

 

Alright, I'm starting to put 2 and 2 together here.

Here is the situation:

When cool, the car starts right up, and runs smoothly.
As the car starts to heat up, the fans go on, and keep the engine between 200* and 220*.

After idling about 15 minutes, the car will begin to run rough and will eventually stall, either on its own or if the gas pedal is hit.

If I go to start the car again, it won't start. I noticed that before I turn the key completely to crank the engine, I hear the fuel pump, which is normal, and then some type of running or pumping sound coming from the intake manifold/fuel rail area.

Now, if I let the car cool down, the car starts right up. interestingly, this time before I crank the engine, i once again hear the fuel, however the "running/pumping" sound coming from the manifold area is not there.


Any clues on what is causing the car to shut down?
Or the sound?

Thanks much!

 

This may not apply at all but maybe you should loosen the fuel tank filler cap so that you are allowing air to easily get into the fuel tank. Possibly when you are letting the engine idle, after 15 minutes there could be excessive vacuum built up in the tank and causing a fuel feed problem. At least this is something simple you can try and can rule out if it does not help. If it does help then something related to venting the gas tank (such as the one way valve for air intake) is plugged or whatever. After the engine has cooled maybe the vacuum has equalized inside the fuel tank and thus starting is successful.

It is just hard to believe that if it idled well for 15 minutes that you have a problem that is NOT related to RUNNING TIME. You burn fuel and that DEPLETES the fuel tank over time. But you are also generating HEAT over time so that might be the issue.

The sound you hear up front apparently only shows up when the engine stopped and is HOT when you try to restart it. When it is COLD you do not hear the sound. Maybe one of your fans is attempting to run to cool the already hot engine. I assume you are in the driver's seat hearing these sounds. Having a companion crank the engine when it is having the problem would allow you to be out near the engine.

 

Thanks much for the reply.
I'll try the gas cap when I get out of work later.

As for the sound, it's definitely not the fan. I have my dad helping me work on the car, so I was listening by the engine to the sound while he was in the car, and vice versa. I'll have to check into it more later today as well.

 

Maybe the most important step is to find out what makes that:

''running or pumping sound coming from the intake manifold/fuel rail area''

There seems at this point to be a one-to-one correspondence between the unusual sound and the unsuccessful re-start. I have a TBI system so I cannot relate to your TPI system very well.