Can you blow an HEI module?

[Bonnewagon]

Buddy has a Pontiac 400 in his GP and he just bought a new HEI but not GM. He wanted to backfit a non-CCC HEI and could not find an original GM. I was explaining to him about timing an engine by removing the spark plugs and grounding the wires, then spinning the engine while setting the timing. He tried that but he thought he could ground the wires to a rebar stake in the ground. 'Like on a house' is what he said. After I admonished him he did it the right way and timed the engine. But now the engine will not start. It has fuel, is timed, but just coughs when you try to start it. I am wondering if by having all the spark plug wires NOT grounded to the engine, could the module have been blown? Or damaged so it will still trigger an inductive timing light, but not ignite plugs under compression. What do you think? And how do you test a module besides just replacing it?

 

[Wageslave]

Dead HEI modules are somewhat rare unless they overheat or are Chinese crap. There shouldn't be any more load on the module if the spark arcs through the spark plug or doesn't arc at all (ground rod).

It sounds more like all the plug wires are one post off or perhaps put on in counter clockwise order instead of clockwise.

I would just swap the module into another car for testing if it is practical. If not, another one is cheap enough to just buy a spare.

Another possibility is the coil that reads the reluctor ring failed or got too weak to give a consistent signal. It should read somewhere between 800-1600 ohms and not vary when the wire is wiggled.

 

[Bonnewagon]

the coil that reads the reluctor ring failed or got too weak to give a consistent signal. It should read somewhere between 800-1600 ohms

OK that sounds like a plan. He verified that the wires were routed correctly. Not knowing what the resistance should be I advised him to bench test it. You grab the distributor in a vise, wire it up as if in a car, make a ground rod out of a coat hanger, point it near the button under the coil, and spin it by hand. If healthy it should bang out a big blue spark and I have gotten the spark to jump over 12". He hasn't gotten back to me but if it failed the bench test I will advise him about the pickup coil test.

 

[Ugly1]

The other thing that is possible (I have done it and my brother caught it) is if the distributor is 180* off. It can run but not well. And will not set the timing. And did he check the module?

 

[78Delta88]

I doubt what he ruined the module. It only triggers the primary to open/close and causes secondary to produce the spark. As far as correct distributor; the HEI he needs is a pre 1981 HEI. 1981 started the C3 non vacuum, non weights, ECU controlled HEI.

I had an 81 Turbo TA and swapped the shaft for the 1980 and had weights and springs to work with.

On the modules it has two sides... Low speed and high speed side. Modules are tested at local auto parts if they have the tester.

Stay away from the lower price units they are pretty much crap.

 

[78Delta88]

The following from local O'Reilly's

I used 1978 Pontiac, Firebird, 400 CID

 

[Bonnewagon]

He did not mention what brand it was but he said he was going to take it back and get a 'better' one. Whatever that means. I think he had a 301 non CC unit and I explained it was the same as a 400 but maybe with a different advance rate, but totally useable. He still bought an aftermarket unit. Yes, he has already learned about being 180° off and I welcomed him to the club. We all do it now and then. He hasn't gotten back to me and I think he is sulking. He is one of those guys that continue to throw money at the problem rather than back up and re-group.

 

[78Delta88]

The one for the 301 should be the same. Just stay away from the $15 units, they are pretty much crap.

HEI is fairly simple, once the reluctor produces the signal the module then triggers the coil and produces spark in its simple form.

Similar to Ford's system except Ford has the module mounted on the fender and then triggers the coil. GM's HEI is all self contained in the distributor, which makes it very convenient. I have a GM style HEI unit for Ford 302 but haven't tested yet. It's a basic unit I picked up from Falcon Global.

I few years back I put the Ford electronic setup on a 65 Mustang that originally came with a point system and it really woke up the engine response on the 289 2BBL. The unit I used came off of a 78 Granada with a 302/auto.

The main Achilles heel of the HEI is the pick up coil. The two small wires break over time and then you have a "crank-no-start" condition. In the interim as the wires wear out, which is prior to breaking, is when you get all the goofy stuff that's hard to diagnose. Even the ohms test can come back ok, yet the pickup coil is on its way to being junk.

 

[Bonnewagon]

The two small wires break over time

Oh yes, been there, done that, got a T-shirt. We were coming home from a springtime Flounder trip and had 103 Flounder fillets on ice in the trunk of my 1976 LeMans. The car died a couple of miles before home. A cop sitting at a speed trap checked us out and said before they spoil he would be glad to take them off our hands. My buddy towed us home in plenty of time. Yup, the pickup wire broke.

 

[Ugly1]

He did not mention what brand it was but he said he was going to take it back and get a 'better' one. Whatever that means. I think he had a 301 non CC unit and I explained it was the same as a 400 but maybe with a different advance rate, but totally useable. He still bought an aftermarket unit. Yes, he has already learned about being 180° off and I welcomed him to the club. We all do it now and then. He hasn't gotten back to me and I think he is sulking. He is one of those guys that continue to throw money at the problem rather than back up and re-group.

Gave away one of those 301 HEI distributors to a guy at work that wanted to put a ‘68-‘69 /400 in a late model Catalina. Would have thought i handed him gold. Was still in good shape too.