HELP! 91 Corvette won't run when hot.
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
HELP! 91 Corvette won't run when hot.
I have a friend's 1991 convertible in my shop and it is driving BOTH of us crazy.
When the engine is cold, it cranks over and starts just fine. Run the car for an hour with the hood closed, shut off the key and then try to start it and it just cranks over. Tested for spark and have plenty. Tested for Injector Pulse and there is none. I also checked and there are no "regular" codes showing up. I checked the CCM Codes and H41 came up. The next day I replaced the ECM under the hood, reusing the old "chip" and figured I had the problem licked.....WRONG! Same symptoms. Crank but no run. Everything i'm reading says the CCM is pretty bullet proof, not to mention a real bitch to buy and install. Any suggestions???????
Thanks,
Jim
When the engine is cold, it cranks over and starts just fine. Run the car for an hour with the hood closed, shut off the key and then try to start it and it just cranks over. Tested for spark and have plenty. Tested for Injector Pulse and there is none. I also checked and there are no "regular" codes showing up. I checked the CCM Codes and H41 came up. The next day I replaced the ECM under the hood, reusing the old "chip" and figured I had the problem licked.....WRONG! Same symptoms. Crank but no run. Everything i'm reading says the CCM is pretty bullet proof, not to mention a real bitch to buy and install. Any suggestions???????
Thanks,
Jim
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
Thanks for the suggestion. I will check the resistance of the injectors when they are cold and then when the problem happens again. The injectors are stock original ones. Would shorted Injectors set the H41 in the CCM?
Engine runs fine when it is warmed up. Just won't run if shut off and try to restart.
Engine runs fine when it is warmed up. Just won't run if shut off and try to restart.
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Thats just as easily a distributer problem...
You DO know that the L98 MUST get permissions from the dist to allow inj cycling, right?
No reference from the dist...no fuel injectors.
If the inj are not cycling at all when hot, there is also a possibility that there is 1 each side shorted out. Being 'bank' fired, 1 shorts that whole banks shorts. Not unusual..The stock inj are trash.
Test coolant temp sensor.
I guess the obvious has been looked at...fuel pressure and regulator health? Pump health?
are you getting the 2 second prime of the fuel pump @ key ON ???? if NO< look at fuel relay AND the oil pressure SWITCH next to it.
Get yer FSM electrical out and start looking at the way the system operates the fuel injection, if there is no cycling at the inj with key ON. They should be HOT all the time...the ecm cycles them with the dist timing.
You DO know that the L98 MUST get permissions from the dist to allow inj cycling, right?
No reference from the dist...no fuel injectors.
If the inj are not cycling at all when hot, there is also a possibility that there is 1 each side shorted out. Being 'bank' fired, 1 shorts that whole banks shorts. Not unusual..The stock inj are trash.
Test coolant temp sensor.
I guess the obvious has been looked at...fuel pressure and regulator health? Pump health?
are you getting the 2 second prime of the fuel pump @ key ON ???? if NO< look at fuel relay AND the oil pressure SWITCH next to it.
Get yer FSM electrical out and start looking at the way the system operates the fuel injection, if there is no cycling at the inj with key ON. They should be HOT all the time...the ecm cycles them with the dist timing.
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
I did replace the Module inside the Distributor, just for conversation sake and the problem continues. Like I said before , there IS spark when the car won't run so I am assuming that the distributor electronics are communication with the ECM.
I will run the car tonight and see what I find with the injectors (checking hot/cold resistance) annd verify power TO the injectors when the car won't run. I did test to see if they "pulsed" when the problem cropped up but did NOT verify voltage with just the key on.
Thanks,
Jim
I will run the car tonight and see what I find with the injectors (checking hot/cold resistance) annd verify power TO the injectors when the car won't run. I did test to see if they "pulsed" when the problem cropped up but did NOT verify voltage with just the key on.
Thanks,
Jim
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
It's the coolant temperature sensor. I just went through this on my 91 earlier this year.
Here is my original thread: http://forums.corvetteforum.com/c4-g...ied-today.html
Here is my original thread: http://forums.corvetteforum.com/c4-g...ied-today.html
Last edited by mcm95403; May 15, 2013 at 12:55 PM.
Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
Thanks for the suggestion but the car runs perfect, when it starts. It is ONLY after you get it fuly warmed up after about an hour of running and THEN shut it off that the "crank but won't run" situation crops up.
Jim
Jim
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
EXACTLY the situation I had - and the sensor tested good as well.
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Thread Starter
Melting Slicks
Joined: Apr 1999
Posts: 2,521
Likes: 4
From: Windham, NH
Well, Deepa (aka: Mike) NAILED the problem!, The injector on #6 cylinder would short out when the engine went into "heat soak" when I shut it off after an hour of running. I checked the injector resistance cold and then when the car wouldn't run and #6 went from 16.5 ohms to .5 and apparently would cause the injector drivers to shut down. As long as I left that injector plugged in, the car would crank and NOT run. I pulled the wires off the injector and it cranked and ran! Now I need to find a REASONABLE price for a set of injectors...
Thanks everybody for ALL of your suggestions.
Jim
Thanks everybody for ALL of your suggestions.
Jim
Le Mans Master
Joined: Nov 2009
Posts: 6,882
Likes: 234
From: Bangkok, Thailand
Well, Deepa (aka: Mike) NAILED the problem!, The injector on #6 cylinder would short out when the engine went into "heat soak" when I shut it off after an hour of running. I checked the injector resistance cold and then when the car wouldn't run and #6 went from 16.5 ohms to .5 and apparently would cause the injector drivers to shut down. As long as I left that injector plugged in, the car would crank and NOT run. I pulled the wires off the injector and it cranked and ran! Now I need to find a REASONABLE price for a set of injectors...
Thanks everybody for ALL of your suggestions.
Jim
Thanks everybody for ALL of your suggestions.
Jim
Bosch III's from Jim at www.fuelinjectorconnection.com then.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
FIC is the go to for fuel injection.
For about $250 you get a matched set of Bosch-III injectors, all the runner/plenum gaskets and o-rings for the rails and injectors. Thats deal can;t be beat.
The service is outstanding. If you have problems with the install, you can get THE MAN on the phone and he will talk you thru it.
When someone gets the "Call Jon" reply to their problem...it IS that simple.
Call Jon.
Search youTube as well for FIC or search fuel injector swap/test or change. There are many good videos on this and many came from FIC...
Good luck. Your LT is cake...btw.