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Dr. Hamman
Dr. Hamman, Chevy Technician
Category: Chevy
Satisfied Customers: 6286
Experience:  30 Years Experience repairing, customizing, and building chevys.
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My 1994 Corvette still will not start after I've new

Customer Question

My 1994 Corvette still will not start after I've new fuel pump, optispark, new fuel filter, and new ignition coil. Fuel pressure is okay. When try starting it, it turns with a slight back fire. Any ideal what is causing this problem?
Submitted: 6 months ago.
Category: Chevy
Expert:  Juan Crespo replied 6 months ago.

Hi there.

Thank you for the service and repair background. Unfortunately, that doesn't tell me if and how those new parts are working. For example, knowing that a new fuel pump was installed does not tell me we have the fuel pressure required for the engine to start and run, and so on with the other parts.

What I would need to know is the following:

  • is compression at an even 120 psi or more per cylinder?
  • is fuel pressure at 41-47 psi?
  • is there injector pulse as indicated by bright steady flashes from a Noid light?
  • is ignition spark at no less than 8KV as measured with an ignition tester?

If the answer to all of the above questions was yes, then the engine should start and run. So, can you check and see what results you get?

Customer: replied 6 months ago.
Juan, This car only has 35,000 original miles on it. The compression is fine. It ran, I turned it off and it didn't start again. That is where I am at this point.
Expert:  Juan Crespo replied 6 months ago.

The only way I know how to diagnose this type of issue is by checking the items I listed above, as by doing so, I've found the little details that have proven to be the root cause of the problem. I'll understand if you don't want to do it that way, in which case I'll opt out and re-open the question in case another expert has a different approach.

Please don't reply until another expert responds or the site will cycle this back to me.

Expert:  Dr. Hamman replied 6 months ago.

I have worked on a lot of these LT1 engines. I have a few questions, does the fuel pump run, and does it have fuel pressure to the engine. Then next does the ignition coil have power to the positive side with the ignition on. Knowing if the coil is sparking strongly when you crank it tells a lot. Also if it is sparking shoot a blast of starting fluid into the intake and crank it up with about 1/2 throttle, if it fires up, runs and dies, that tells us it isn't getting fuel injected. These basic tests should get you pointed in the right direction.

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