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Old 05-17-2020, 11:39 AM
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AdamIsAdam AdamIsAdam is offline
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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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  #2  
Old 05-17-2020, 12:34 PM
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george kujanski george kujanski is offline
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Sounds like the box....with electronics, one failure mode is a "latchup" in the logic somewhere and you need to cycle power to reset. One popular cause internally is a component gets hot, (usually due to poor heat sinking, i.e. assembly error), and the part goes into shutdown. Cycling power gets it back, until it gets hot again, etc.

George

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  #3  
Old 05-17-2020, 12:54 PM
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MSD in the past has always been very good at servicing their stuff, and reasonably priced to do it. I haven't sent anything in since they sold out, so I can't comment on the current situation. Maybe contact them and explain the problem and make the arrangements to send it in. This assumes you've done a very thorough job of checking all the connections and all grounds. And made sure its wired correctly to begin with. Main battery connections should be straight to the battery, etc.

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  #4  
Old 05-17-2020, 02:46 PM
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Yes, I tried calling MSD yesterday and they were closed despite it being normal working hours. I'll try again Monday.

the ground wire goes to the frame (not the battery). The power wire connects to a thick, main power wire that goes to the starter relay (it's a Ford, remember, so it's got those heavy relays that are wired directly to the battery, usually mounted on a fender). I do now know where the other end of that heavy wire is going to, I think the main fuse box. I'll double check. Then there's the switched power wire that goes to the ignition switch.

I do not have a heavy key chain, and the ignition switch feels solid. I've tried wiggling it a lot while driving and cannot cause the short manually.

I've checked the volts on the ground at that main starter relay and it's the same volts as the battery itself.

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1964 LeGTO
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  #5  
Old 05-17-2020, 03:06 PM
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I would move the ground to the engine block or cylinder head at a minimum. If you have to extend the wire, make sure its the same gauge or larger. I would do this no matter if it cures the problem, or once the box is repaired. Ideal would be take them both directly to the battery. I've done what you did running main power from a Ford style solenoid, but I've never tried grounding to the body, or chassis, and wouldn't recommend anyone else do it either.

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  #6  
Old 05-22-2020, 02:08 PM
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I ran new home runs all the way to the battery. I added an inline LED to the switched power from the ignition switch just to monitor that should I lose power again to see if that's the cause. It started up and ran last night. Today, it's DRIVE TIME!

i'll report back.

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1964 LeGTO
469, M21, 3.42

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1968 Pontiac LeMans Convertible
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  #7  
Old 05-22-2020, 06:29 PM
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Got to take it for a nice 15 minute ride today and experienced no problem whatsoever. Knock wood. Then the rain started closing in on me.

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1968 Pontiac LeMans Convertible
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