Help! Tach Signal Disappears - Holley HP EFI

[ROKN69]

Hi guys (and gals),

I have an interesting issue I've been chasing for over two months. I have a '69 Camaro with an LSx (RHS block and heads) that is ProCharged making over 1000 HP.

Issue: When the car reaches full operating temperature (not before) it will lose the CRANK signal. This happens at first under heavy acceleration (about 50% or more throttle), but as you drive the car it happens under slight acceleration, and finally after about another 5 minutes after the symptom first presents itself, it will happen even if you're just on the throttle cruising at a steady RPM. When under acceleration, if you keep your foot on the throttle (instead of lifting immediately) when the engine quits (due to loss of CRANK signal) the engine will stay dead. As soon as you lift your foot off of the throttle, the engine will spring back to life like nothing ever happened.

Over a year ago a similar event happened, and it was only under heavy acceleration when the engine quit running. As soon as I would lift the throttle it would spring back to life. It was repeatable and only when the car warmed up. I didn't keep running the car like I am now, though, so I don't know if the problem would have progressively gotten worse (as it is today). I took the car to my tuner, Dave from Auto Trend EFI, and Dave said that the car was missing some necessary grounds (head to head ground, direct ground to battery, some loose connections, etc.). After Dave worked on the car, it ran perfectly for a bit over a year.

Now the issue has presented itself (it feels like the same issue, anyway), again, and we've checked and all the grounds are intact. All connections are secure. We've changed the crank and O2 sensors (the O2 was due to another issue). We've pulled a system log and it shows that the CRANK signal is disappearing, but the CAM signal is still present. We tried a different Holley HP EFI ECU, with the same, identical behavior. We have changed the wiring harness, and verified no breaks in the lines. The throttle cable is nowhere near any wiring harness or cables (it is NOT a drive by wire setup).

I believe I've covered everything we've done, from a troubleshooting perspective. I'm hoping that someone will read this and either have experienced the same issue or point us in the right direction to resolve this nasty bug. Your help is very much appreciated!

Best regards,

Roger