Hey yall, pretty new to the corvette scene, my dream car has always been the C3 and I finally got an 81 for cheap with a great frame but some less than reliable internals. For note, the previous owner appears to have replaced the original carb with an ez efi system. The issue I'm having is when going for initial start-up, I'll get fuel sprayed into chambers and an initial spark and combustion but it won't turn over after.

Through trouble shooting, I've discovered that when just turning on electrical and manually pulling the throttle, it will spray fuel into chamber, and then fuel pressure shoots up and the injectors stop operating. After about 3 minutes, pressure normalizes, but the injectors remain inoperable until turning electrical off and back on.

Fuel lines have been disassembled and reassembled, ensuring solid fuel is arriving to the engine, each sparkplug carries a strong spark, distributor cap has been cleaned.

The car was idling a bit rough, but still operating good for a while, then when I filled the tank with gas, she refused to turn on after.

Any suggestions are helpful as I'd rather fix the car myself and learn more about maintaining this beautiful piece of machinery rather than handing it off to a mechanic.

 

I would try the battery ground strap and check it's clean at the battery and also the frame Also the horn relay under the hood to check those are clean and tight. This happened to me before and most of the time it's something very easy . I hope you find it

 

Just to clarify, when you say “it won’t turn over” you mean that nothing happens when you turn the key? No starter clicking or engagement?
If that is the case, something to check is the ignition switch at the base of the steering column. Additionally check that when it acts up and does not turn over, cycle the gear selector around if auto, if manual pump the clutch a few times. The neutral safety switch could be sticking, if so, this will also prevent the starter from doing anything.

 

I'll get initial stages of the engine turning on, get maybe a cycle of combustion, but it doesn't sustain or fully turn over the engine.

 

What injectors??? An '81 had a carburetor with an electronic solenoid fuel mixture system.

 

So is it a starter issue or engine not running issue? like the starter stops turning the motor over? Or the starter is cranking away and the motor is just not firing?

If the starter stops operating, as mentioned above, check where the negative cable connects to the frame, unbolt it and clean well. This condition worsens when everything is hot(causes an even higher resistance connection)

if the engine is not firing, well there’s a lot that could be the problem there. You said you got fuel and spark, timing and compression only things left.
You could try seeing if it’ll fire off of starter fluid,
That’ll check spark/timing/compression

 

OP stated he has an EZ EFI system installed by a PO.

100%, try some starter fluid. The EZ EFI system keeps the stock distributor, right? I'm assuming that the PO also replaced that, with a 4-pin HEI distributor. Can you post some photos to confirm?

If the car runs for a few seconds with starter fluid, you'll know the issue is likely in the fuel system.