1994 LT1 momentary loss of ignition
09-28-2018, 03:29 PM
#1
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1994 LT1 momentary loss of ignition
I have a 94 Corvette w/ LT1 that will experience a momentary loss of ignition, almost like the car 'sneezed'. The MPH and the Tach will drop to zero, the vehicle continues to run OK, MPH and Tach come back to life. As soon as this event happens, the Service Engine Soon light comes on, I will hear the electric fans come on and continue running until I shut the vehicle off. This happens after running the vehicle for a while, shutting off the vehicle for a period of time (60 minutes etc.) and on the return trip this event happens within 10 minutes. The new Optispark has less than 1,000 miles on it, plugs and wire were also replaced. Any help would be greatly appreciated. A mechanic said the 'trouble' codes indicate a weak/bad ignition module/coil. I don't understand how this would make the electric fans come on or why the vehicle continues to run. Thx Dean
09-28-2018, 04:24 PM
#2
Race Director
Is this a $69 junk optispark, a $500 msd also-junk optispark, or a NOS ac delco OEM one using the oem misubishi sensor? (And not a chinese rebuild - currently your only choice from the dealer)
other items to check include grounds, and also make sure ecm mem/cal chip isnt loose or falling out of its socket like on my 93
(wait you said 94 never mind)
other items to check include grounds, and also make sure ecm mem/cal chip isnt loose or falling out of its socket like on my 93
(wait you said 94 never mind)
Last edited by dizwiz24; 09-28-2018 at 04:25 PM.
09-28-2018, 04:42 PM
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Is this a $69 junk optispark, a $500 msd also-junk optispark, or a NOS ac delco OEM one using the oem misubishi sensor? (And not a chinese rebuild - currently your only choice from the dealer)
other items to check include grounds, and also make sure ecm mem/cal chip isnt loose or falling out of its socket like on my 93
(wait you said 94 never mind)
other items to check include grounds, and also make sure ecm mem/cal chip isnt loose or falling out of its socket like on my 93
(wait you said 94 never mind)
09-29-2018, 03:21 AM
#4
Race Director
I had a bad ground that caused all kinds of weird things to pop up and then magically get well. It was corrosion in between a gang of ground wires on the driver side of the block at the bell housing. Probably can’t see it from above. I had to put the car up on jack stands and go under. Once I got all those junctions cleaned on that stud, everything got well again.
09-29-2018, 04:49 AM
#5
Race Director
The Opti is an AC Delco. I had experience with a failing Opti prior the the replacement; this momentary loss of ignition while driving seems different. I'm still puzzled by both fans coming on / running when this happens. I didn't think about a bad ground; where would I look for the ground?
i had problems with a gm remanufactured ac delco unit (and it even had a mitsubishi optical sensor spraypainted black to make it look new again).
in my case, the car would start but then stall after a minute or two as soon as it got warm.
wouldnt restart until after cooling down for 6 hours
all this said, a gm remanufactured unit would be one of my top 3 choices - esp given that you cant find nos anymore (without luck)
09-29-2018, 09:09 AM
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I had a bad ground that caused all kinds of weird things to pop up and then magically get well. It was corrosion in between a gang of ground wires on the driver side of the block at the bell housing. Probably can’t see it from above. I had to put the car up on jack stands and go under. Once I got all those junctions cleaned on that stud, everything got well again.
09-29-2018, 11:53 AM
#9
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The fact that the engine continues to run after everything else goes dead tells me that its not an opti, coil, or module. I would definitely be looking for a bad ground or the ECM. The fact that its so predictable and repeatable makes me think its heat related which leads me more toward the ECM.
10-01-2018, 11:00 AM
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Jvettman and dizwiz24; I'm following your thinking. The fact that the loss of ignition is momentary (fractions of a second) and that the vehicle keeps running OK; a bad ground is a good possibility. If it's a bad coolant sensor, could the activation of both fans be simultaneous with the momentary loss of ignition? I.e. is the coolant sensor activating both fans drawing too many Amps (electrical terminology... not my best topic) thereby causing the momentary loss of ignition? Once both fans are running, there is no subsequent ignition issue, car runs OK. I'll be taking the Vette to my mechanic with this additional information. Thx
10-01-2018, 11:41 AM
#12
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I have my '94 wired to activate both fans and besides a load on the alternator, there no other effect. At idle it will loose 100rpm when the fans kick on, under power it is not noticeable. It should not affect the ignition.
09-14-2020, 04:32 PM
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A follow-up to my Sep 2018 post; I replaced the battery in summer 2019 (I don't know if the battery weak or possibly a broken side post), this resolved the momentary loss of ignition (there was still a hesitation), and I still have the fan issue. After taking the car out of storage in summer 2020, the issue with the electric fans continue. I replaced the coolant temperature sensor (front of water pump), this didn't resolve the issue. The vehicle starts and runs; there is a slight hesitation when the service engine soon light illuminates and both fans turn on. I took the vehicle to the repair shop as I'm out of guesses, patience and don't have the skills to diagnose further. I did share with the service shop the suggestion of a bad ground and the location, I also shared the thought of a heat related issue with the ECM.
Last edited by BlackIce94; 09-15-2020 at 04:23 PM. Reason: Missing info