Help! 94 stock corvette starts and runs well cold, after 20 or so miles it starts to cut out then stalls

[ish8686]

I am at the end of my rope, this is a low milage car, 52000, the car restarts and runs well after it cools down. The fuel pressure and volume is good, we are not loosing the ignition or injection signals, the ecm power and grounds are good, I have installed redundant grounds. THERE ARE NO CODES the ecm will set codes when any sensor is disconnected. I suspected the opti-spark distributor even though we installed a new MSD distributor 4 years ago. Any loss of high or low resoulition signal should set codes, but if one of the sensors failed when hot it could cause this condition so I removed the distribtor and sent it to MSD, and they rebuilt it. MSD told me they found a bad sensor and replaced it, needless to say I was very frustrated when the problem reoccoured. We have installed a new delco ignition control module and a new ignition coil. I am open to any ideas, I am hoping someone has had a similar problem and solved it, HELP!!!
I am a ASC certified master technition with years of chevrolet experience but this one has me baffeled.

 

[DrDyno]

Symptoms sound familiar...

I was a professional wrench long before ASC certification. And, although I don't know how the gasoline pickup is accomplished in a C4 gas tank, as I read your symptoms I kept thinking (old school) you have sediment in your gas tank.

(Old school, once again)... engine starts up fine. As the fuel pump creates negative pressure around the fuel pick up (usually a screen), any sediment starts to move in that direction. Eventually, enough sediment clogs the fuel pickup. Engine shuts down, pressure is relieved and, over a period of some time (long or short, depending) the sediment settles back to the bottom of the tank and the car restarts. I would humbly suggest you pull the fuel pump/sending unit from your gas tank and have a look-see.

Respectfully,

John
St. Petersburg, FL

 

[Robertwav1]

Sounds like an excellent idea...maybe change the fuel filter as well and get that all out of the equation. I know I changed mine around 50K just because.

 

[kpic]

Before your vehicle goes on our DynoJet, please make sure:

1. The vehicle has at least 1/2 tank of fuel (premium recommended)
2. The fuel filter is new or very recent
3. The engine oil has been changed very recently (supercharger oil too, if equipped)
4. The tires are in good and would pass state inspection

Fuel filter is second and a lot of tuners recommend a GM filter.

 

[Wegone]

Another thing to check is the rubber line that connects the fuel pump to the line in the tank, the line can swell and the plastic clamps get old and break.

 

[Hib Halverson]

Have you connected a fuel pressure gauge then road tested with it taped to the windshield to "watch" what the fuel pressure does when the driveablility problem starts?

Have you connected a scan tester and observed the ECM data list when the driveablity problem occurs? Better yet, if your tester will take data, have you tried setting it up for a "snapshot" with manual trigger then, when the driveability problem begins. taking some data to see what the egine controls are doing when the problem begins?

A 94 (except LT5) has partial OBD2 capability. If you have a scan tester which will read OBD2 codes, see if any are stored. The OBD2 part of the 94 and 95 systems will not turn on the MIL even if a current OBD2 code is set.

When the engine finally stalls, try doing an immediate fuel pressure and spark gap test.