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96 Lt4 Mystery

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Old 05-05-2018, 11:42 PM   #1  
MikieG1971
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Default 96 Lt4 Mystery

The car just died. Has started once cool only to warm up and die after a few minutes.
I had some MAF sensor related codes, so i replaced it. The battery was a bit weak so i replaced it.
So in the spirit of heat related problems, i inspected the coil and ICM. They looked like originol equipment and looked really bad. You guessed it. I replaced them.
STILL NO JOY!!!
I am looking for suggestions, tests and proceedures etc. I do have the factory service manual. What section would you think i should be looking in.
I am supposed to be taking this car to the C4 Gathering in a couple weeks. Really bad timing for sure!
Thank you for your input.
MikieG
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Old 05-06-2018, 12:18 AM   #2  
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Check fuel pressure. Had an LT1 that would run like a beast cold, get about 20-30 minutes int the drive and it bogged and cut out. Turned out to be a bad fuel pump and clogged filter ( tank rust was the cause). Although you shouldn't have tank rust you may still have a fueling issue.
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Old 05-06-2018, 08:33 AM   #3  
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See if this helps:


Please don't throw any more parts at the problem till you have explored the Opti problem. Your symptoms sound like this is something you shoudl consider.
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Old 05-06-2018, 09:10 AM   #4  
MikieG1971
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I am aware of the opti spark issues. I amnot ruling it out. But you have to admit, the second an LT engine stutters, the oti is always blaimed immediately.
The items i replaced were already in need of replacing.
Really pises me off if it turns out to be so. I just flushed the coolant system.
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Old 05-06-2018, 10:23 AM   #5  
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Quote:
Originally Posted by Space387 View Post
Check fuel pressure. Had an LT1 that would run like a beast cold, get about 20-30 minutes int the drive and it bogged and cut out. Turned out to be a bad fuel pump and clogged filter ( tank rust was the cause). Although you shouldn't have tank rust you may still have a fueling issue.
Start with this. If the engine dies, listen for the 2 second prime to see if you can hear it.

Would be good to check for spark also.
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Old 05-06-2018, 10:24 AM   #6  
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Lt1’s dont have fuel issues

its the optispark. My guess is its not an oem quality optispark
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Old 05-06-2018, 12:58 PM   #7  
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Lt1’s dont have fuel issues

That's quite a broad statement. Fuel pumps do die, filters get clogged and injectors fail as well.
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Old 05-06-2018, 01:40 PM   #8  
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Originally Posted by billschroeder5842 View Post
See if this helps:

https://www.youtube.com/watch?v=famCZkXppYM

Please don't throw any more parts at the problem till you have explored the Opti problem. Your symptoms sound like this is something you shoudl consider.
TL;DR that guy installed 3 different opti's and it turned out to be the ground strap under the brake booster that grounds the engine computer.
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Old 05-06-2018, 02:03 PM   #9  
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Doesn't sound like an opti to me at all.

I agree, check fuel pressure. The start when cold but then dying when warm normally sounds like icm or coil, but with those ruled put I'd check fuel. Could by a leaky regulator, or a blockage in the delivery system (filter perhaps)?
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Old 05-06-2018, 02:25 PM   #10  
dizwiz24
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As electronics get hot, short circuits occur.

Outside of vapor-lock issues of old carb’d cars, ive never heard of a the fuel system shuts down when it gets hot.

You’ll get a mix of replies on here from early tpi c4 guys that had failure prone early injectors whereas the lt1 multec? style is pretty bulletproof.

this is why id look more at the ignition, with a big emphasis on the optispark.

Last edited by dizwiz24; 05-06-2018 at 02:26 PM.
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Old 05-06-2018, 03:58 PM   #11  
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Quote:
Originally Posted by dizwiz24 View Post
"Outside of vapor-lock issues of old carb’d cars, ive never heard of a the fuel system shuts down when it gets hot."
Happens all the time and it is a very very typical symptom of a failing electric fuel pump. I have seen it multiple times over the years. It is probably a crap shoot as to whether it is the electronics within the pump failing or the pump physically seizing when the heat soak sets in. Sometimes the relays will act this way too, as in a heat soaked starter relay which is very typical as well. When the symptoms start, sometimes you can coax the pump along by keeping the tank full which keeps the fuel/tank temp down.

I own a fuel pressure gauge to identify this exact issue and have helped several friends, family members and coworkers over the years.

As previous members have stated, I concur... The first thing I would do is attach my fuel pressure gauge, if that isn't the issue I would look at the other items that succumb to heat soak, i.e. coil and relays.
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Old 05-06-2018, 04:08 PM   #12  
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Originally Posted by Krusty84 View Post
Happens all the time and it is a very very typical symptom of a failing electric fuel pump. I have seen it multiple times over the years. It is probably a crap shoot as to whether it is the electronics within the pump failing or the pump physically seizing when the heat soak sets in. Sometimes the relays will act this way too, as in a heat soaked starter relay which is very typical as well. When the symptoms start, sometimes you can coax the pump along by keeping the tank full which keeps the fuel/tank temp down.

I own a fuel pressure gauge to identify this exact issue and have helped several friends, family members and coworkers over the years.

As previous members have stated, I concur... The first thing I would do is attach my fuel pressure gauge, if that isn't the issue I would look at the other items that succumb to heat soak, i.e. coil and relays.

Im not saying your experience isnt true.
Have you seen fuel pump/when hot issues on a c4 Lt1? Or some Ford or Chrysler with EFI ?
Ive been on here awhile and havent seen it - yet have seen tons of optispark problems.



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Old 05-06-2018, 10:34 PM   #13  
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Quote:
Originally Posted by MikieG1971 View Post
. They looked like originol equipment and looked really bad.
MikieG
Maybe the fuel filter looks original too.
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Old 05-06-2018, 10:58 PM   #14  
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Quote:
Originally Posted by dizwiz24 View Post
Im not saying your experience isnt true.
Have you seen fuel pump/when hot issues on a c4 Lt1? Or some Ford or Chrysler with EFI ?
Ive been on here awhile and havent seen it - yet have seen tons of optispark problems.
I would counter that you've seen lots of issues that get blamed on Optis. A lot of them are something else that gets dome at the same time, like plugs, wires, coils, or ICMs.
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Old 05-06-2018, 11:06 PM   #15  
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As i said earliwr. I had a list of defects i already knew needed repair. I handled them myself to keep repair labor costs down.
The heat issue immediately had me thinking of coil and ICM. Now with them changed, (could be bad outta the box ) with new ones, i feel like this could easily be fuel pump, filter or Opti related.
My mechanic goes on jury duty tomorrow. Hell be there all week. Looking like this LT4 wont be at the Gathering this year.
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Old 05-07-2018, 12:58 AM   #16  
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You can rent a fuel pressure tester from any of the auto parts stores. Even if you have to get out and drive it with the gauge hanging out of the hood, its how I diagnosed my issue.
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Old 05-07-2018, 02:02 AM   #17  
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Quote:
Originally Posted by dizwiz24 View Post



Im not saying your experience isnt true.
Have you seen fuel pump/when hot issues on a c4 Lt1? Or some Ford or Chrysler with EFI ?
Ive been on here awhile and havent seen it - yet have seen tons of optispark problems.



Nope, never. Probably has never happened in the history of the world of LT1 C4 Corvettes.
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Old 05-07-2018, 09:22 AM   #18  
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Id like to reiterate, i really appreciate everyone taking time out of their lives to share their experiences with me. Thanks everyone!!
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Old 05-14-2018, 08:58 PM   #19  
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Drum roll please.... But first. This thread had alot of great advice. Last year my other 96 died. Turned out to be ICM. This one.... wait for it...
Opti spark!!!
My son is just amazed by the smooth power of the LT4 now!
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Old 05-14-2018, 09:26 PM   #20  
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Congrats on sorting out the issue!

Just out of curiosity how many miles were on the old opti?
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