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A friend of mine has a 94 Vette engine "undocumented conversion" into a 1988 XJS. Can't get a shop to work on it, he tows it in and they call back in a day or two and say come and get it. Ignition problems for half a year, now will not start and run (cranks ok). He has tried new parts with so called car show experts without a shop, and is getting no where.
My research shows 94 LT1 as a special set of ignition components, that are all different by 96..
1. Can he just replace all the ignition system with new 1996 component?
2. Do most owners find 94 ignition find the system reliable?
3. Is there a simple test to confirm Distributor is working, as he wants to change it, and the access requires a lot of removals including the water pump.
4. He has Haynes manual for corvettes 86 to 96, but says LT1s are not included???
Appreciate any expertise on the ignition system
Rgds
David
Google "Corvette Optispark Ignition". Tons and tons of info out there. Also used in Camaros, Impalas, Firebirds, etc. I would think all problems and cures would be familiar to most general repair shops.
I can't speak to the exact matter at hand but in somecases the V8 conversions are so sloppily done that a typical repair shop just doesn't want to bogged down untangling a rat's nest.
Thank you
Spent some time on site and found many T/S themselves, without the help of full list of shop equipment, (that would quickly rule out rabbit trails)... Not having OBD2 test port is adding to lack of shops wanting to get involved.
Looks like observing TACH while cranking and the Two ( 2 second fuel pump tests are do-able as a start.)
Rgds
David
I'm an expert on the optispark and Lt1 system in general. Here is what you can do to get started. It's a very simple system that mostly relies on a hitachi optical trigger wheel inside the optispark unit with a hi and lo resolution signal that the PCM uses to trigger ignition, spark and injector pulses. .
Hook up a spark tester to the coil output, when cranking you should get spark, fuel injector clicks and fuel pump.
- If you do then you have a good hi and lo res signal from the opti unit, check for spark at the plugs and fuel delivery to the rail.
- if you only get fuel pump, the high res signal may be bad or the ignition module may be bad, or the opti pigtail is bad, replace all three (start with the pigtail)
- if you get injector clicks, the hi and low res opti signals to the PCM are good, if no spark then change the ign module
- if you get neither fuel pump, injector clisks or spark, the Low res signal may be bad, replace the opti and check the pigtail.
- if you get fuel pump and spark for only a few seconds then stops, you have a VATS problem (add VATS defeat device or program PCM and remove VATS, I can do this)
When checking and replacing the opti there is an unusually long plug with connections deep inside the opti as shown below, you must be EXTRA careful to make sure you have a good connection here with no misaligned pins. It's kind'a easy to misalign the pins inside the opti when removing and replacing things. If any of the pins inside the opti plug come out of alignment you lose the hi, low or both signals from the opti. I have fixed MANY LT1 opti cars that didnt run but where "everything was replaced" and a few mis-aligned pins inside the new opti from a ham handed mechanic was the only problem.
More difficulty arises when the retrofit installations are not done properly, and most are not. I've seen where an inexperienced installer will wire the fuel pump and fans directly to a +12 ignition source so those PCM triggers can't be used for diagnostic purposes, that's not helpful , its unsafe and needs to be corrected if this is the case.
Last edited by icsamerica; Dec 13, 2024 at 09:27 AM.
94 vette LT1 engine in 88 XJS
