Yesterday my engine started cutting out really bad at engine speeds above 4500 rpm, particularly noticeable at WOT no matter what engine speed. It seemed like the secondaries were opening but weren't feeding any fuel. Clogged jets or needle & seat on the rear circuit.

I got tired of piddling with the old carb, so I put a brand new Holley Street Avenger on the thing today, and the WOT problem went away. Low speed response is awesome, and there's no smoke from the exhaust at idle any more (another recent occurrence). But it's still cutting out at higher RPM's. It's never done this before.

Is it possible for the HEI module or in-cap coil to fail partially? The cap, plugs, and rotor only have about three-thousand miles on them.

Maybe the carb problem fouled a few plugs causing the symptoms I'm describing? Bad plug wires? Or should I try swapping the module and coil?

Yes. The conventional wisdom used to be that when an electronic module failed, the car wouldn't run. That isn't true. I have seen failures where the car ran crappy. In my experience, the car ran crappy pretty much all the time, though.

HEI modules have a reputation for not providing decent spark after 4500-5000 rpm. I have not personally had that problem, and GM uses HEI on many of the high performance crate engines. I still tend to shove an MSD box in anything I care about.

Just like any other coil they can get weak. It has happened to me. Try another used coil and see if it picks up.

Thanks guys.

I've had modules completely fail in the past, without warning. The car just refused to start. This may be the first time I've seen one go bad without completely dying.

I picked up a new set of plugs this afternoon and I have a spare module that I'll put in when I swap the plugs. If that doesn't do the trick, the coil is next on my list.


There just ain't anything else to change. MSD even crossed my mind a few times, but I've had good luck with HEI for too many years to shell out that kind of money right now.

Chad, I have a good HEI with a new module and newer aftermarket coil (50K volts) laying around at home. If you want it for parts send me an e-mail - you can have it.

Chad, check the cap and rotor. If there is a bunch of "dust" in there it could pass the current at low rpm but cause problems at higher rpm when the demand is higher. Wires could break down, too, and this might only show up at higher rpm.

Chad, I've had an HEI do exactly what you're describing. I had an Accel coil on there. I replaced the coil and gone. Apparently the coil was scattering only at higher RPM's.

Correct me if I'm wrong, but your post sounded like you fixed the problem by putting the new card on?

Don't overlook pick-up coil(pulse coil in bottom-your electronic points). Everytime vacuum advance moves those 2 little wires bend & can break internally. You usually get bucking & missing-till it dies (for good).

I had a pick up coil act like that once. Coils are easier to swap first though.

How's that 383 coming Chad?

Well, I looked all over town today for a Cap-a-dapt so I can run a regular MSD coil. No luck. All anyone offered was the ugly Accel "hat". I'm hoping my friend with the speed shop will have something. If not, I'll have to get an overnight from Summit or Jegs.

I've wanted to get the heat producer out of the cap on this thing for a few years, now I have a good excuse to do so.

Adam, I appreciate the offer, but I need this thing back up to 100% by yesterday, so I'm gonna go with an overnight from Jegs if necessary.

Pat & Old66SS, I'll definitely check on those things. The dust is a very high probability right now because I've driven on quite a few caliche (dirt) roads lately. I'm gonna pull the cap and rotor and clean everything thoroughly and check the module and reluctor.

Scott, the 383 is all done except for the assembly. I was gonna assemble it in October, but then I got moved to Houston and lived in a hotel room for three months.

Now I'm in Corpus Christi and my 383 parts are still in Baton Rouge. I'm flying to BR next weekend and driving all my parts and tools back on a U-Haul truck to put in storage until we move everything here on the 20th. Then I can start on the 383 assembly.

I spent $4000 today on a new living room and dining room set for the wife, so there are some items that we won't have to move. Once I finish getting the Camino back in good tune, I'll have spent over $4500 in the last two days. So I have to cut back a little in the near future. And I guess I won't be starting my bike build before the summer.