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Discussion Starter #1 (Edited)
The truck just died on the way back to the shop from lunch. Engine shut off and it would crank but not start. Narrowed it down to either the HEI module or pickup. Installed a new pick up on the side of the road (fun) and it fired right up. Drove it to the shop, but on the way home, once the module warmed up a little, it stated to intermittently misfire. Similar feeling to when a COP is going bad. I can see the tach kind of wandering when it’s happening. Figured it was a defective module. Ordered and installed one the next day (today) and the same thing happens. It does it at idle as well.

Another defective module, or pickup bad also? What are the chances the module and pick up go bad at the same time?
 

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If you're sure this is a spark issue, then look hard at your grounds and the 12v+ wire at the distributor. Is this a coil in cap or remote coil distributor?

Another note, the quickest way, at least for me, to nail down a distributor issue is to slap in a ready to run spare. I have not found this idea real popular among many guys, but you'll know in 15 minutes if the problem is in the distributor or if it isn't.
 

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Discussion Starter #3 (Edited)
If you're sure this is a spark issue, then look hard at your grounds and the 12v+ wire at the distributor. Is this a coil in cap or remote coil distributor?

Another note, the quickest way, at least for me, to nail down a distributor issue is to slap in a ready to run spare. I have not found this idea real popular among many guys, but you'll know in 15 minutes if the problem is in the distributor or if it isn't.
I’m fairly certain it is. I know for sure the module was completely dead. A new one at least got the truck up and running again. Anything is possible and, while it would be real coincidental, I could certainly have another issue in a different system that all happened at the same time.

It’s an all in one HEI unit. 355 with an Edelbrock AVS2.

Ordering a whole new distributor is an option. Having a spare wouldn’t be a bad thing. Unfortunately, about a month ago, I just replaced the cap, rotor and coil with MSD parts!
 

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You were going great until the end.
MSD parts, eh!
I’m with nailhead.
Carry a spare.
Hei’ s can be bought for 50 bucks.
 

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Discussion Starter #5
You were going great until the end.
MSD parts, eh!
I’m with nailhead.
Carry a spare.
Hei’ s can be bought for 50 bucks.
Lol my feeble brain thought that MSD was the top shelf of HEI equipment! Any recommendations?

Wouldn't it be unusual to have a pick up coil cause an intermittent misfire? I checked the wiring from it and all looks to be normal, so I don't believe it to be a short. I need to check the ground at the back of the head and the chassis. Battery cables are tight. In my mind a pick up coil either works or it doesn't.
 

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Regarding a spare, locally I've bought from Advanced Auto and they've been fine. And the idea is that if you confirm the issue is in the dizzy after installing the spare, then fix the original yo use as the spare. And I've used BWD for aftermarket GM hei parts. They've worked well for me.

MSD is not what it used to be. Now you pay for the name, not the quality.

I have to disagree with you about the pickup either working or not. Check the wires to it. Its not a go or no go situation.
 

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Stock HEI's were know for breaking the pick-up wires with age(vibration, heat, and advance mechanism movements), wire would break inside the insulation but look intact when examined, movement of the vacuum advance plate would creatre a intermittent signal and eventually outright failure.
 

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Coil could be shorted out ( a few windings ) and burning modules out.Or leaking High voltage as another Post said.
Change the module and the coil .Put a rotor on in case it has a problem as it could be leaking High voltage spark as well.
 

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Replace everything with ac delco parts and be happy.

The only msd thing I run anymore is the cut to length plug wires.
 

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Discussion Starter #11
I went ahead and just ordered a whole new HEI unit. It started backfiring through the carb when it was misfiring in the way home today. It’ll stay parked until Saturday now. I’ll update y’all when it’s put in. If that doesn’t fix it it’ll be back to the drawing board, but man it would be crazy to have the module completely fail and another system have a problem at the exact same time!
 

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Stock HEI's were know for breaking the pick-up wires with age(vibration, heat, and advance mechanism movements), wire would break inside the insulation but look intact when examined, movement of the vacuum advance plate would creatre a intermittent signal and eventually outright failure.
This is a distinct possibility if the distributor is older. One way is to get a quick diagnosis is to unplug the vacuum advance and see if things change.

Better way is to disconnect from the module and use an ohmmeter while gently tugging and moving the wires. And if the wires break while gently tugging, then you have definitely found your problem.

Pick up coils are cheap and easy to fix. If you end up needing one, make sure it is for a Chevy and not another GM vehicle.
 

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Discussion Starter #14
New distributor fixed the issue. 50 bucks on amazon is just hard to beat. We’ll see how long it lasts though. Thanks for y’all help! I’ll do some testing on the old one and fix it for a spare!
 

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Just as an afterthought . . . I had similar issues when I was using solid wire (metal) spark plug wires on my 350 Chevy with an electronic distributor - a big NO-NO! New distributor and suppression wires fixed the problem.
 
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