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Old 05-17-2020, 11:39 AM
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AdamIsAdam AdamIsAdam is offline
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Join Date: Oct 2006
Location: Long Island, NY
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Default Default Engine dies while driving - tach drops to zero (MSD ignition)

Hey there, old Pontiac friends! I'm back lurking! yes, I sold my GTO () and I have not been around here much, and I have to say, I have not found other forums to be as good, friendly, and knowledgeable. So I'm back!

I've got two other cars now and the one I'm writing for help with is a Cobra. I've always wanted one and this winter picked up a really nice Factory Five. I'll post a few pics. I bought the Cobra this winter and only put about 300 miles on it so far.

On to my problem:

My Cobra just developed a problem that is getting worse. I can be driving or idling, then all of a sudden, the tach drops to 0 and the engine stalls as if someone turned the key off. If I'm moving, I can turn the key off and then on again and it will restart, or if I'm at a light, I just restart it and it's fine. Either way, the key must be moved to off then on again. I was thinking the ignition switch might be going bad except I do not lose any other electrical aside from the engine (gauges, lights, turn signals all remain on). Plus, today I was driving and decided to turn the key off while in gear and the tach did NOT drop to zero when I did that; then I turned the key back on and it continued running of course. The problem is happening more frequently now too.

I've checked for spark with the MSD paper clip trick and it's fine, which MSD says that means the box is fine. I've checked the ohm reading on the magnetic pickup and it's within their specs. All grounds appear to be ok. I'm at a loss as to what to look for.

The car is a new-to-me Factory Five Cobra that only has 1,600 miles on it, but is 6 years old. It's a 347cid with a holley DP and mechanical fuel pump.

IGNITION SYSTEM:

MSD Digital 6AL box, MSD 8598 distributor. Coil blaster 2. I actually replaced it two months ago because the coil died on me. Totally different symptoms: car stumbled and died when I first started it in my driveway and then wouldn't restart. Coil did not have continuity. New coil fixed it right up. I actually have two new coils because I changed from red to black, so I have a new spare.

Cap, rotor and plugs are new. Car runs great aside from the electrical issue.

The tach is from Speedhut.

I hate to point to the little red MSD box, so please advise on how to troubleshoot. As I said, the entire car looks brand new, so no rusty ground bolts, and every ground wire I can see is really well secured.

Thoughts and suggestions welcome!

And here's some pics...
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1964 LeGTO
469, M21, 3.42

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