Help! strange new problem

[Bentas1ent]

my 1989 c4 has a 5.7 litre in it and it starts great when cold and will run for as long and as fast as i dare to run it. However once i shut it off and try to restart it all it does is backfire a couple of times then it starts but one by one the cylinders shut off until it dies. Then it wont restart until it is cold the next day. Any ideas out there???

 

[ex-x-fire]

Possibly the coolant temp sensor isn't reading right when its hot.
Get a fuel pressure tester & test the psi all the way til it dies. It should hold pressure after the engine is off, for a while.

 

[boomdriver]

my 1989 c4 has a 5.7 litre in it and it starts great when cold and will run for as long and as fast as i dare to run it. However once i shut it off and try to restart it all it does is backfire a couple of times then it starts but one by one the cylinders shut off until it dies. Then it wont restart until it is cold the next day. Any ideas out there???

I'd also take a hard look at fuel pressure/flow. Coolant temp sensors can do strange things for such a simple sensor.Always clean/check the connections of related sensors.
Its sounds like when parked the filter or screen in the tank will allow trash to settle and float away when there is no suction from the pump, but when running the screen gets clogged and it takes several hrs being parked for the junk to drift away so the flow can resume later. As long as there is pressure, or tension on the system the trash is held in place in the filter or screen.
Symptoms can be so intermittent that it may not happen for a week, then it happens everyday. Between the clogged screen in the tank, and a dirty inline filter, it can be difficult to diagnose. I have pulled an inline filter and dumped a tablespoon of rust and other solid junk out of the inlet side.
Test fuel pressure, key ON, while running and after key off. pressure should be steady around 40 lbs idle, not jumping around more than 1 or 2 lbs, and the pressure should hold nearly the same for 20 minutes after shut down and slowly drop pressure to zero over the next few hours.
If the pressures are the least bit questionable, replace the filter AND the screen. Most people replace the pump since it has to come out to change screens and if the filter is plugged, that trash had to go thru the pump to get as far as the filter..

Another remote possibility is a clogged cat. When cold it may pass gas but as they heat up they close up and kill the engine. That does not exactly sound like your symptoms, but at that age its possible and will happen eventually, just like the fuel filters.

 

[Schrade]

Leaking injectors, or a ruptured FPR diaphragm will allow a cold start but a hot start will be a problem, unless the fuel is WELL-vaporized. Both of those things will be problems for hot restarts.

With a cold motor, turn the key, but don't start it. Pull the vacuum line off of the FPR, and see if you can smell fuel, or if it's wet with fuel.

If it is, DON'T necessarily replace the FPR yet; rather cap the fuel line BEFORE the FPR, and do a static fuel pressure test. Don't 'pinch' like some say to do NOPE. If you 'pinch' tight enough to really block flow, you could damage stuff. If you don't 'pinch' tight enough, and gas still gets by, you'll get a false test result, and won't know it.