LT1 backfires when left in sunlight
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
LT1 backfires when left in sunlight
As strange as this sounds my 92 lt1 starts up quickly then runs rough and then sounds like fire crackers out exhaust for about 30 seconds. It then runs smooth and has full power with no issues. It will do this everytime it is left outside in the hot sun for an hr or more. Shows only code 32 for egr. I have replaced opti, wires,plugs,FIC injectors,checked fuel pressure and fuel leak down with injectors is normal. This does not act up long enough for my shop to find problem. I thought I had it fixed from last year but now its hot in south Florida again.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Try cycling the fuel pump a few times( key on and off cycles) before starting I am betting if really hot youare boiling the fuel out of the rails. A couple of priming cycles will get cold fuel into the rails and bet it goes away.
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
Thanks I have tried that with same results. The cts readings on dash seems ok as well. Would a bad coil or icm act weird like this. Maybe my ecm is acting up but it shows code 12
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
12 is what you get at the begining of the transmission to verify the there is communication. It is not a ECM error not sure about other modules. ICM might be it or coil if temps in the sunlight greater than driving and just might be. Certainly not something to discount as not possible as othen they do not throw a code when bad.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
You said you have to leave it in the sun for an hour or more?
The ICM has been known to get flaky at high temperatures, but being that it is bolted to the cylinder head it seems like it would get way hotter just from the car running than it would from sitting in the sun.
Just to make sure I understand all completely.
If you park it and let the engine cool down, say overnight, does it do the same thing?
IE say you park it in the sun at noon today and go out at noon tomorrow and try it. Trying to determine if it has something to do with it possibly being engine heat related or strictly sunlight only.
The ICM has been known to get flaky at high temperatures, but being that it is bolted to the cylinder head it seems like it would get way hotter just from the car running than it would from sitting in the sun.
Just to make sure I understand all completely.
If you park it and let the engine cool down, say overnight, does it do the same thing?
IE say you park it in the sun at noon today and go out at noon tomorrow and try it. Trying to determine if it has something to do with it possibly being engine heat related or strictly sunlight only.
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
This is a awesome triple black vette that I take to car shows here in sunny florida but it is so embarrassing when I start it up to leave and it backfires so loud out exhaust. I have been trying to figure this out just dont have the money right now to throw at it guessing with no codes.
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
It will act up even if the car is left outside overnight and the engine is cold . If it is hot outside and left in the sun with the engine hot or cold it will run rough then backfire out exhaust for about 30 seconds.
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Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
When I took it to a well knownshop thats what they said. It seems like shops down here dont want to work on lt1's. They said change the opti for every hicup so thats what I did. I was hoping someone else might have had a problem like mine. When it acts up it feels like the plugs are not fireing right then it starts to burn un burned fuel in the exhaust.
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
I know you don't want to throw parts at it, and I certainly never recommend doing so, so I'm just asking this:
When you did the opti did you also do routine tune up stuff like plugs and wires?
Nevermind..... I see you said that in the top post.
What about that code 32? Have you run through the troubleshooting for that? EGR can do some extremely stupid stuff.
When you did the opti did you also do routine tune up stuff like plugs and wires?
Nevermind..... I see you said that in the top post.
What about that code 32? Have you run through the troubleshooting for that? EGR can do some extremely stupid stuff.
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
If I roll it out of the garage even with a cold engine and leave it in the sun it will act up. But if I start it up in the garage it will run great. I'm not kidding and this has a lot of people baffled. I really love this c4 but it is driving me crazy.
Thread Starter
Instructor
Joined: Jan 2010
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From: Coral Springs Florida
It is a 6 speed with a negative egr. The diaphram is shot but when I pushed inside against it and moved it the engine would run rough then smooth out when I let it go back down. No vacume leaks holds steady at 20#.
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
Thanks for your help guys. When I changed the opti I also replaced the short wire harness from opti to connection under injector cover. The new opti with plugs and wires made no difference. It really feels like the engine is not fireing the plugs right or the engine is loading up with fuel. Are you guys leaning towards icm/coil too. If I get a new icm which brand do you recomend and also do you suggest I replace the coil as well
Thread Starter
Instructor
Joined: Jan 2010
Posts: 106
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From: Coral Springs Florida
If this is happening when engine is cold in open loop I dont know what else is left other than icm/coil or bad ecm. The ecm is very hot to the touch when the car is left outside in the sun under the black hood. This year ecm does not have any heat sink on top of it like the newer ones. But you would think with a hot engine in the compartment it would act up when driving. this only happens on startup.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
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From: Tampa Florida
What is the coolant temp @ when you start the engine and the problem happens?
Is the CTS sensor funtioning properly?
What type and size are your current fuel injectors?
What is the fuel rail pressure when you first start the engine?
Your '92 is a "batch fire" setup - all 8 injectors fire at once, since the problem goes a way quickly after start up - for whatever reason - perhaps your puddling more fuel than you should onto the intake valves when the thing does the extra pulse widths @ "cold start".
