Help, broken down, no spark hei

Derek Townie · Post subject: Help, broken down, no spark hei (Sun Jan 22, 2012 11:38 am)

Hi folks, my 62 town wagon with a 74 duster 225 just cut out on me. It has no spark but does seem to have power to the positive on the coil. I have only done a handful of miles since converting to hei. Has a new msd blaster 2 coil.

What should I test next?

Thanks team! Got to get this beast off the road and back home today.

Derek

Derek Townie · Post subject: (Sun Jan 22, 2012 1:41 pm)

Turns out I fried the control module.. Now I just need to work out what I did wrong!

Sam Powell · Post subject: (Sun Jan 22, 2012 2:48 pm)

Was there a heat sink under the module?

Sam

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Fab64 · Post subject: (Sun Jan 22, 2012 6:11 pm)

How did you determine the problem? I'd be interested in any findings as I am in the process of doing this conversion right now. Thanks, and good luck.

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Derek Townie · Post subject: (Mon Jan 23, 2012 8:39 am)

I have it mounted on the fender and have a thick peice of rubber under it. It was also cold yesterday so I don't think it was a overheating issue. I took the module in to Autozone (not my favorite but certainly the closest) and they confirmed it was dead. I got a generic replacement.

With the new module it started right up but only got me another 3 miles before the same thing happened. I got one more module which got me home.

I did the conversion a couple of years back but have been restoring the truck so never got to test it.

Now I'm thinking I should get a good quality module and add a relay.

Anything I am missing?

Thanks

Derek

SlantSixDan · Post subject: (Mon Jan 23, 2012 9:29 am)

Thick piece of rubber…? Why? What's needed is electrical grounding and thermal conductivity (heat sink), not electrical isolation and thermal insulation, which is what rubber will do.

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Reed · Post subject: (Mon Jan 23, 2012 10:01 am)

What Dan said. I am surprised the motor even ran with the rubber under the unit. I suspect that the unit is grounding through the sleeve around one of the mounting screws. Remove the rubber and replace it with a piece of aluminium and be sure to use heat-sink compound.

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Derek Townie · Post subject: (Mon Jan 23, 2012 12:04 pm)

gotcha, I'll do that. Guess I mis-understood what the heat-sink was for. So I take it that the idea is that the heat-sink helps transfer the heat so that it can be dissapated over a larger surface (the aluminum).

The unit was grounded ok as far as I could tell.

Thanks for the insight.

Reed · Post subject: (Mon Jan 23, 2012 12:24 pm)

The heat sink helps dissipate heat, however, since the HEI module grounds through the metal surface on the bottom, the heat sink also acts as the ground for the HEI module. Like I said, you are lucky the unit worked since it was largely insulated by the rubber you placed under it.

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Sam Powell · Post subject: (Mon Jan 23, 2012 8:29 pm)

Run a ground wire from one of the module hold down screws over to the engine block. It should be at least as large as a number 12. I am betting that module got hot as a firecracker before it died each time. I have a good sized chunk of aluminum with heat sink compound under the module and under the sink, which is bolted to the fender. The compound is essential.

Sam

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