repeat LT-4 just stops running
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,526
Likes: 104
From: Stafford Va
repeat LT-4 just stops running
I have posted a similar issue before but it did it again. I will be driving down the road and the car shuts down and will not restart unless I let it sit for 5-10 minutes. After that it runs great with no issues for another 100 miles. I had it in the paint shop and they called and said it started and was idling and then stoped running and would not restart. It was after hrs when I got up with him so I said I beat it will start tomorrow morning. Every now and again I get a low idle and stalls. The engine has 20k miles, new distributor and rotor, wires. Any good ideas are welcomed.
Racer
Joined: Apr 2005
Posts: 408
Likes: 0
Are any codes being tripped? Try the old wiggle trick. While running, move the engine harness around all over, wiring to the opti, coil, and ICM particularly. THere are also grounds back by the top driver side bolt where the tranny bolts to the engine. If nothing, then I would suspect the ICM is getting hot and failing.
Team Owner
Joined: Aug 2005
Posts: 34,988
Likes: 515
From: Riverside County Southern California
Co-winner 2020 C4 of the Year - Modified
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Are any codes being tripped? Try the old wiggle trick. While running, move the engine harness around all over, wiring to the opti, coil, and ICM particularly. THere are also grounds back by the top driver side bolt where the tranny bolts to the engine. If nothing, then I would suspect the ICM is getting hot and failing.
try this first
...ensure the MAF is connected
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
When it quits, THAT is the time to do some diagnosis to find out the cause. Engines require hot spark and spark at the right time, fuel and air and in the correct ratio and cylinder compression in order to start and continue running. Put a grounded wire in the boot of a spark plug wire while someone cranks to see if you have a snappy spark, it should be at least 1/2" long. Use a timing light to see if the timing is correct during cranking. Measure fuel pressure, it should be 35-42 psi and it should hold up for at least 1/2 hr with the ign off. Spray starting fluid into the MAF to see if it will start, if it does you have a fuel delivery problem. Use a noid light on an unplugged injector socket on each bank and see if it pulses during cranking. You can make your own noid light with an LED and a series 680 ohm resistor. The homemade noid light has to be connected with the correct polarity to work. Last, measure compression. Somewhere in these tests you will find one or missing vital components that allow engines to start and run.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
no-no
back in the dark ages this was done to check for spark...modern electronic ignition systems can self-destruct while attempting to fire a 1/2 inch gap...use a 'known good' spark plug gapped o,040-o,060 inches with a good plug body ground to check for spark.
BUT:
my bet is your fuel pump is near complete failure...BTDT
BUT:
my bet is your fuel pump is near complete failure...BTDT
Melting Slicks
Joined: Mar 2008
Posts: 3,022
Likes: 3
From: Chandler Arizona
I have the feeling that it must be the ICM (when it gets hot). Possibly the coil? Usually you can hear the fuel pump kick on when you turn the key to the on position, but you don't start the engine.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
I have posted a similar issue before but it did it again. I will be driving down the road and the car shuts down and [B]will not restart unless I let it sit for 5-10 minutes[/B]. After that it runs great with no issues for another 100 miles. I had it in the paint shop and they called and said it started and was idling and then stoped running and would not restart. It was after hrs when I got up with him so I said I beat it will start tomorrow morning. Every now and again I get a low idle and stalls. The engine has 20k miles, new distributor and rotor, wires. Any good ideas are welcomed.
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Melting Slicks
Joined: Jun 2004
Posts: 3,253
Likes: 2
From: Castro Valley CA
Follow the advice above for codes( http://www.digitalcorvettes.com/foru...56&postcount=9
) fuel pressure and injectors.
When you have eliminated the fuel side then follow this routine (This is one of the best threads I have found):
http://www.camaroz28.com/forums/showthread.php?t=601565
Excellent resources here as well:
http://shbox.com/1/4th_gen_tech2.html#opti_test
http://shbox.com/1/4th_gen_tech1.html
) fuel pressure and injectors.
When you have eliminated the fuel side then follow this routine (This is one of the best threads I have found):
http://www.camaroz28.com/forums/showthread.php?t=601565
Excellent resources here as well:
http://shbox.com/1/4th_gen_tech2.html#opti_test
http://shbox.com/1/4th_gen_tech1.html
Thread Starter
Melting Slicks
Joined: Mar 2002
Posts: 2,526
Likes: 104
From: Stafford Va
Just a recap, this LT-4 is in my 64 Corvette Grand Sport that I built. It has a high volume Walbro fuel pump with the pressure constant around 45#. The engine has quit when the motor is cold, after a few minutes of idle and when it s warmed up just driving down the road. It goes a while before it happens again. It will crank right after it dies but will not start. If I sit there for 5-10 minutes it will crank right up and run as if nothing happens. New MSD opti and new h20 pump no leaks . I will try Sidney's approach and for grins replace the ICM if this does not work. Fuel pump is working fine I have a on off switch for it as well.
Should note the computer has been swapped for a PCM for LESS programmed OBD-I.
http://s152.photobucket.com/albums/s173/vstol/
Should note the computer has been swapped for a PCM for LESS programmed OBD-I.
http://s152.photobucket.com/albums/s173/vstol/
Last edited by vstol; Jul 25, 2010 at 04:28 PM.
Melting Slicks
Joined: Feb 2006
Posts: 2,753
Likes: 15
From: backwoods upstate ny
might try fast cooling the ICM , if no help chill the computer...just need
an 'air bubble' with a blow off nozzle in place of the normal tire fill chuck...a 15 sec air blast from 6'' away should do more to lower device temp than 10 min in still air.
an 'air bubble' with a blow off nozzle in place of the normal tire fill chuck...a 15 sec air blast from 6'' away should do more to lower device temp than 10 min in still air.
Advanced
Joined: Aug 2008
Posts: 59
Likes: 0
Try and understand how each component works before you start throwing parts We replaced the ICM looking for a no hot start, and all we really needed to do was check for spark while it was cranking to see that ours was not bad. So it's got a nice new ICM for no other reason than troubleshooting blind.
(I'll sell you the old one really cheap if you want to throw some used parts at the problem.)
Our problem with the car cutting out was the coil had a crack. The car not restarting hot was a seperate issue of the injectors. (could have also been the coil, but after our latest dilema with the no hot start, we suspect injectors all along as a shadow issue.)
Get a led test light if you plan on checking injector pulse. When the car won't restart, grab an ohm meter and check resistance in all injectors. If any are low, 10 ohms or less, leave them disconnected them and try and restart the car.
Oh, and pull the coil and check it for cracks (ours fell apart in our hands) That solved the intermittent cut out.
(I'll sell you the old one really cheap if you want to throw some used parts at the problem.)
Our problem with the car cutting out was the coil had a crack. The car not restarting hot was a seperate issue of the injectors. (could have also been the coil, but after our latest dilema with the no hot start, we suspect injectors all along as a shadow issue.)
Get a led test light if you plan on checking injector pulse. When the car won't restart, grab an ohm meter and check resistance in all injectors. If any are low, 10 ohms or less, leave them disconnected them and try and restart the car.
Oh, and pull the coil and check it for cracks (ours fell apart in our hands) That solved the intermittent cut out.
Advanced
Joined: Aug 2008
Posts: 59
Likes: 0
