Won't run/start when warm

[louswan77]

Hi Guys:
I'm new here and have a new girlfriend with a 1991 Corvette 5.7L 350-V8 Fi-8. She 's had this sitting around in her yard for over 2 years due to problems and other priorities. The car starts fine when cold, runs fine but after warming up the problems begin. It will NOT START UNTIL ITS COOLED DOWN FOR OVER AN HOUR, I had a fairly good mechanic spend considerable time troubleshooting and replacing various parts, fuel filter/strainer, man air temp sensor, throttle pos sensor, knock sensor, O2 sensor, Ign control sensor, coolant temp sensor. Still have same problem. I've researched and see sometimes the pick-up coil can be the cause however I think this was ruled out. He said he was getting a spark and tested the pick up coil. He's now suggesting the computer module?
Please help, I'm new to working on a Vette and need somewhere to start.

 

[Rob]

Welcome to the Corvette Action Center!

I'm going to move your thread into the C4 tech forum for greater exposure.

 

[gmjunkie]

If the ignition pick up and coil are good, Sounds like could be the injectors are leaking down and flooding it!
Hold the accelerator to the floor and crank it, if starts firring and starts,I'd start checking for a leaking injector.

 

[louswan77]

Thanks

Thanks

Welcome to the Corvette Action Center!

I'm going to move your thread into the C4 tech forum for greater exposure.

 

[louswan77]

Thanks, I'll check it out.

I have tried in the past, holding accelerator down, never could get it to fire up.

If the ignition pick up and coil are good, Sounds like could be the injectors are leaking down and flooding it!
Hold the accelerator to the floor and crank it, if starts firring and starts,I'd start checking for a leaking injector.

 

[DonB]

Does it fire at all when hot???? Did he test the pick-up coil when Cold and then HOT? There should be very little difference in resistance. I don't have the spec. right now but here's a video.

HEI Distributor Pickup Coil Test - YouTube


If you put a module in replace the pick-up coil while you are in there. These parts are NOT that expensive and be sure to use AC/Delco. The cheap Chinese crap will get you into trouble.

 

[Robertwav1]

Fuel pressure reg could be bad. Hard starting when warm is a symptom.

 

[louswan77]

got spark

We got good spark when hot, kind of rules out the pick up coil. I think. Checking fuel injectors.

Does it fire at all when hot???? Did he test the pick-up coil when Cold and then HOT? There should be very little difference in resistance. I don't have the spec. right now but here's a video.

HEI Distributor Pickup Coil Test - YouTube


If you put a module in replace the pick-up coil while you are in there. These parts are NOT that expensive and be sure to use AC/Delco. The cheap Chinese crap will get you into trouble.

 

[louswan77]

Good fuel pressure

Replaced fuel pump and getting good pressure, suspecting maybe injectors, gonna check them next. Thanks

Fuel pressure reg could be bad. Hard starting when warm is a symptom.

 

[Robertwav1]

Just to be sure your pressure could read good and the regulator have a small leak when car is shut down reason for a hard start when warm...a leaking injector as stated will do the same and fuel pressure could read good as well...

 

[louswan77]

Thanks

Ok thanks. Will continue to check. Although, don't have a hard start at that point, WILL NOT START AT ALL. But, never have smelled gasoline for what it's worth.

Just to be sure your pressure could read good and the regulator have a small leak when car is shut down reason for a hard start when warm...a leaking injector as stated will do the same and fuel pressure could read good as well...

 

[louswan77]

Fuel Injectors out or tolerance with ohm values when hot

I ohmed out the fuel injectors, when cold they all were within spec 11-16 ohms, when hot, 3 of them fell below one ohm, other's were also low6-10 ohms, several were ok. I plan on changing them all out, I think this should solve my problem.:L

Ok thanks. Will continue to check. Although, don't have a hard start at that point, WILL NOT START AT ALL. But, never have smelled gasoline for what it's worth.

 

[aklim]

I ohmed out the fuel injectors, when cold they all were within spec 11-16 ohms, when hot, 3 of them fell below one ohm, other's were also low6-10 ohms, several were ok. I plan on changing them all out, I think this should solve my problem.:L

Ohm tests are misleading when you consider that the injector can ohm out well but have clogged filters, nozzles, etc. It just says that the coil is in good shape and since there is more to an injector than the coil.....

I take mine out for testing and cleaning every 3 years. The "before" reading always comes out lower than the "after" reading and isn't as consistent. Varnish build up or whatever clogs the filter basked, etc, seems to get built up after a couple 3 years.

 

[louswan77]

Thanks

Well I hope this is the problem as I've got em all out now, putting the new ones in soon.

Ohm tests are misleading when you consider that the injector can ohm out well but have clogged filters, nozzles, etc. It just says that the coil is in good shape and since there is more to an injector than the coil.....

I take mine out for testing and cleaning every 3 years. The "before" reading always comes out lower than the "after" reading and isn't as consistent. Varnish build up or whatever clogs the filter basked, etc, seems to get built up after a couple 3 years.

 

[louswan77]

Runs great after replacing fuel injectors

Got the new fuel injectors in, car runs great, happy to be able to ride again.

Well I hope this is the problem as I've got em all out now, putting the new ones in soon.