Bill Boardman

Gentlemen,
I have a 94 K-1500 Burb, 5.7 TBI, OBDI. Truck starts fine cold and runs fine warm. If I shut it off warm and let it sit for five minutes, or more and then try to restart it will start and then die. Trying to restart after this is very difficult, if not impossible until it cools down. If, on the warm restart I give it some gas (2000 rpm+) for a second, or two it runs fine and drives fine again until another warm restart. I've checked the fuel pump pressure (11.5psi) and rebuilt the TBI ( it had 240,000miles on it). When running it is fine with no problems. If anybody has any suggestions on what else I should be looking at It'd be greatly appreciated. I am at my wits end trying to figure this out.
Thanks in advance.

Irish_alley

from memory the pressure is on the low side. idea is 12-15, the lower pressure might be from a dirty fuel filter. can you hear the fuel pump prime when you just turn the key to "on" for a few seconds?

Bill Boardman

Fuel filter is new, according to my service manual the pressure should be 9-12psi. Yes, I can hear the pump turn on. It seems to be an issue with heat soak on a component. I've checked everything, but the ignition control module, it just doesn't make any sense why it would run fine when gassing it on restart. If I gas it a little on the restart it stays running and runs fine, it pukes out if I don't gas it a little. I know it sounds a little convoluted, the first thing we thought of and checked was the fuel delivery and it appears to be working like it should. A friend had suggested the IAC, but it idles fine when running and doesn't exhibit the usual IAC problems. I thought maybe someone on this board has dealt with this problem before. Being OBDI there aren't a lot of things that could go wrong. I don't want to pull out the parts cannon and start throwing money at it. Thank you for the input.

Irish_alley

yup rechecked, psi should be 9-13 but a 12 psi regulator.
heres the spec numbers for the sensors
Troubleshooting sensors and how to test
did you check the fuel pressure when the engine was warm?
another thing that comes to mind is a vacuum leak thats only present when warm and giving it gas may counter the leak

Bill Boardman

Yes, checked pump pressure warm. Did find one bad vacuum hose, but replacing it didn't make any difference, it was for the purge solenoid. Thanks for the troubleshooting link. I'll have to get it warm and start checking those parts. I'm leaning towards the ignition module as those electronic parts don't like heat. If I remember correctly the ECM powers the pump through the fuel pump relay until start up and then the oil pressure switch is supposed to take over powering the pump. From what I remember there was a change in 94 and I can't find a definitive serial number range where that change occurred. So it's a possibility that the pressure switch is being wonky when warm and needs that pressure to remain up long enough to let it close. Thanks again.

Irish_alley

the ecm does energizes the relay for a few seconds to prime the pump then waits till ignition pulse from the distributor, once signal is received the ecm will energize the fuel pump relay. if no pulse is received the and the OPS sees 3 psi (maybe a few more but no more than 5) it will bypass the fuel pump relay. dont remember hearing about the change in 94 but thats not saying it didnt happen.

Bill Boardman

Okay, I don't remember all of the details, but I seem to remember something about how the pump is energized. I'm probably wrong on that, I've read so much trying to get insight on what the problem might be. It doesn't set the check engine light and that seems to make it harder to diagnose. It'll probably be something simple once I get it figured out.