No Start backfiring through intake
 

I just completed installation of Lloyd Elliott heads, new cam and new tune on a 1993 Corvette LT1. The engine fired and ran better than it ever has; Lloyd has great skills and provides a great service. In other words, it is a bad ass engine. I drove it a little with open headers and then installed a new exhaust. Then I could not get it to start - it would crank and occasionally backfire through the intake. I confirmed fuel pressure, injectors firing, spark and was starting to believe it was the opti as everyone is quick to point out on this forum (it's the MSD 8381 vented with maybe 5,000 miles). BUT My pal then moved the harness and tried starting again, it fired and ran perfectly. No missing, good idle, and sounded great through new exhaust. We shut if off and restarted, wiggled wires and it stalled, wiggled again and it started. It was running great when we left that night. Came back the next day and I could not get it started no matter what I wiggled. After 9 hours, I had opened the wire loom and traced every wire, found and repaired one bad ground and one ecm +feed broken. Still no start and still backfiring. I am going back to look over the wiring one more time later this week and test all of the ignition circuits. My question is opti related: considering the above and the fact that the engine was running really well (when it did run) can I rule out the possibility that the opti was installed incorrectly? I really see no reason to blame the opti but I will tear down if I can't find anything else. Thoughts? apologies for typos, I am at the beach or a day to cool off and working from a phone. Thank you

Nice: office at the beach!

Given the above, it seems like more wires are compromised and timing (and Opti) are good. Special attention to which wires need wiggling. Small (or none) cracks can hide larger discontinuities. Like all else on modern cars, relatively small voltages control EVERYTHING and many do not age well.

That is what I am thinking...how could it run so well if the timing is not correct. I'm hoping to find a bad ground and another option is iCM. I ordered acdelco model. We shall see...and thanks for your input.

There is a ground on the front of the drivers cylinder head/block which was probably removed for the install.....

Possible that is dirty or loose?

EDIT:
Also, what did you do for a tune?

Yes that ground is there. I have it on the bracket for the power steering pump but I just saw a pic on shoebox where it is on the coil stud. I will relocate it and also recheck that it is a good ground with meter. I'm almost positive it is a ground issue.

The tune was provided by Lt1 PCM based on modifications I have made. I have had this engine running and I would say the tune is good because it idled and revs well. No highway test yet though. I plan on doing a real data tune with same guy to maximize performance at some point. Need to get it started again first, lol !! Thanks for your input

Intermittant connections are a PITA! Your 'wiggling' is the big clue.