I have an 85' D100 with the lean burn system. I installed the GM HEI module shown in the diagrams here on the site. My problem is the truck has ran better but after the installment it has gotten more difficult to start. And now it will almost not start at all. It just turns over and over sometimes trying to fire. I did replace the coil with a cheap model. Is it possible my coil might be going bad?

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85' D100
225cid
A833OD

I'm wondering if you are still using the lean burn setup.

Yes.

What coil are you using? I've been running an Accel 8140 Super Coil with my HEI for a while, and it works just fine.

I ran the same coil for more than ten years with points and a ballast resistor - probably not the best combination - and never had starting or other obvious ignition problems.

By the way, how is your module grounded? A bad ground can cause real problems. Also, the modules can die slowly.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

Well, I think I figured it out. After installing the HEI module, I also increased the spark plug gaps from .35 to .45. Thinking too much of a gap could be the problem, I decreased it to .40. So far so good, I hope this does it.

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85' D100
225cid
A833OD

That suggests you might want to take a close look at your secondary ignition components (cap, rotor, plug wires and coil). 0.045" is a reasonable gap with HEI; if it caused starting problems for you it means that one or more of your secondary ignition components is breaking down under high load. It will be worth your hassle to order in a NAPA Echlin long-tip rotor # MO-3000, which has a longer tip to reduce arcing in the distributor. Don't buy an Echlin or Accel cap, though!

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