Ignition Control Module Issues on my 71

[wsurf4me]

I've recently run into an issue with ignition control module failures on my 71 C10. I've done some online searching but haven't found anything that really outlines how to troubleshoot and solve the issue. Hoping someone can point me in the right direction.

Now the details -
71 C10, purchased a year ago, SBC with aftermarket HEI distributor, aftermarket 8mm plug wires. I put about 10k miles on it without issue, however in the last 2 months and appx 1000 miles I have experienced ignition control module failures twice. About 3 months ago I installed Dakota Digital HDX gauge cluster and wired up the tachometer, prior to that there was no tach. After the first failure I inspected the tach wire and connections and replaced the cap and rotor. Also installed a Pertronix Flame Thrower module as I read they were "more robust". Just lost that module the other night driving down the road at 30-40 mph, engine backfire and shutdown. I was able to restart and make it a few more miles before it failed for good. I replaced it roadside with a spare and it started right up. First failure was the same except after first shutdown and restart the tach was reading 0.

I've reached out to Dakota Digital, can't imagine that's the issue but that seems to be when my issues started. Any suggestions or guidance on how to troubleshoot further? What impedance/resistance should I see at the tach wire at the distributor?

[kwmech]

Are you putting the heat paste under the module when installing?

[wsurf4me]

Originally Posted by kwmech

Are you putting the heat paste under the module when installing?

Yes I am. First one I inherited from previous owner but it had the thermal compound. The Pertronix I used to replace it came with white thermal paste which I used. The one I just put in is an old Delco Remy, comes with the clear paste which I used.

[dmjlambert]

I'm pretty sure there is no such thing as clear thermal paste. That is probably dielectric grease for the terminals only, which won't work as a thermal compound.
Just curious, have you tried just disconnecting the tach wire at the distributor and see if the problem the module seems to be causing goes away? The tach wire shorting to ground is a method of making a kill switch, it will disable the spark, so a bad tach or bad wire shorted to ground, or intentional short to ground will disable the engine. I mention this because you indicate tach is new to the truck and you didn't have problems before it.

[RichardJ]

Do you have anything connected to the "R" terminal on the starter solenoid? If you do, remove it. Fold the wire back on itself and tape it up.

[Richard]

Are you using the stock resistor wire to the distributor? The lower voltage from that wire will cause more current through the module.

[wsurf4me]

Originally Posted by dmjlambert

I'm pretty sure there is no such thing as clear thermal paste. That is probably dielectric grease for the terminals only, which won't work as a thermal compound.
Just curious, have you tried just disconnecting the tach wire at the distributor and see if the problem the module seems to be causing goes away? The tach wire shorting to ground is a method of making a kill switch, it will disable the spark, so a bad tach or bad wire shorted to ground, or intentional short to ground will disable the engine. I mention this because you indicate tach is new to the truck and you didn't have problems before it.

I thought the same but the instructions say it's "special silicon lubricant" for heat conduction. I may still clean it and replace with white thermal grease, that's what was on the previous module. I ran a new wire when installing the tach and went thru grommet on the firewall. At this point that's the next move if I can't find anything else.

[wsurf4me]

Originally Posted by RichardJ

Do you have anything connected to the "R" terminal on the starter solenoid? If you do, remove it. Fold the wire back on itself and tape it up.

Thanks for the suggestion, I replaced the starter almost a year ago with a Powermaster mini, the wire for the R terminal was removed then.

[RichardJ]

Richard,
>>The lower voltage from that wire will cause more current through the module.<<

NOT TRUE. If you increase the resistance in a Series Circuit, it reduces the current.

[VetteVet]

Here is some reading for you.

https://www.google.com/search?domain...D%3A1%3B&hl=en

[RustyPile]

Originally Posted by Richard

Are you using the stock resistor wire to the distributor? The lower voltage from that wire will cause more current through the module.

Not exactly true.. A term used to describe a resistor is: Current LIMITING device..

Follow this link to Wikipedia:

https://en.wikipedia.org/wiki/Resist...20other%20uses.

[v30crewcab]

it does have the ground strap that bolts to the coil right?

[wsurf4me]

Originally Posted by v30crewcab

it does have the ground strap that bolts to the coil right?

Yes it does.

[wsurf4me]

I went ahead and purchased some good thermal paste, cleaned the other stuff out and applied to the old Delco Remy. Inspected all the wiring for cracks or damage, everything looks good. Checked the ground back to the battery, 0.3 ohms should be more than good enough. I went ahead and disconnected the tachometer wire as an experiment since I don't really see anything else that could be causing the problem.

[Richard]

Was thinking of brown out situations volts X amps equals watts. Lots of fuses and circuit boards replaced in my career due to low voltage. A device wants a certain amount of watts to operate. If volts drop, amps will typically increase. Did not consider the resistance. None the less, operating a load outside of rated specs causes inefficiency's, added stress. heat and early failure. Guessing OP has addressed this as there has been no mention of changing the wire.