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Username Post: HEI Trouble        (Topic#357157)
Posts: 2

Reg: 07-09-19
07-09-19 05:42 AM - Post#2770260    

Help please. I have a 1985 C10 that is not firing to the spark plugs. It has power to the distributor (pink wire) when key is turned to ON and START. I have replaced the cap, ignition module, coil and rotor and still no spark. I am curious about the four wire plug that comes into the back from the cab. Unfortunately, all the schematics I find don't show this, just pink and black. It has the 3+2 IM. I did replace the rotor contact and spring. Plugs seem to be making good contact. Any help would be greatly appreciated. Thank you.

Senior Chevytalk Moderator
Posts: 24961
Loc: Austin, TX 78748
Reg: 05-09-00
07-09-19 06:08 AM - Post#2770261    
    In response to superhornedfrog

Welcome to the site superhornedfrog. TCU alumni?

Common problems with no spark are due to the distributor. The pick up coil under the distributor is a common one. For those failures, I replace the entire distributor. You can ohm out to check a pickup coil. Since you replaced all the other parts, your problem is likely to be the pickup coil.

Another problem is ECM control. The electronic control module can fail or cause annoying problems. Read the ECM post the top of this forum. There is away to bypass it permanently.

'83 Silverardo XST - ZZ4 powered
'95 Jimmy SLT (Bought @131,814)
'96 GMC Jimmy LS Ret. @236651 miles

Valued Contributor
Posts: 3680

Reg: 04-15-05
07-09-19 08:18 AM - Post#2770278    
    In response to superhornedfrog

Rock auto shows two different types of HEI distributor for those engines, depending on if they are carburetted, and the one below I think you have, for the EFI engines.

Carburetted engines run a non EFI 4 terminal HEI module, along with mechanical and vacuum advance. Both run an epoxy coil located in the distributor cap.

The module for the EFI system is what is referred to as a "7 pin" EFI-HEI module. There are two magnetic pickup terminals on one end, and a set of 2, then 3 terminals, to make the 7. There should be a 2 wire, and a 3 wire connector out of the distributor, then, a 3 wire to the cap.

There is no mechanical, nor vacuum advance on these distributors.

The 2 terminals in the inner end of the 5 are the power input and spark event output to the coil.

The 3 on the end are input, power, and signal fire back to the module to set the spark advance, these 3 wires go to the EFI control computer.

All timing functions are done through the EFI computer, none are done in the module.

The magnetic pickup in both types is housed in an outer reluctor housing that sits outside the reluctor on the distributor shaft. These reluctors have a lower housing, the magnetic coil, and an upper reluctor with 8 "teeth" in it.

To replace the reluctor, do so by replacing the entire reluctor assembly, NOT only the magnetic coil. Reason, the teeth on the outer reluctor are sensitive to alignment to shaft center, and if the reluctor is not reattached dead center, reluctor teeth on both reluctors can be damaged to the point of non-function. I built a special centering tool to set the relcutor center, never seen another one in use. Best to replace the reluctor if needed as a full assembly, they are not expensive.

As far as the coil, they have a wire from them to their mount in the cap, and a metal buss bar from under the coil back to the center terminal of the cap connector, then down the loom into the distributor TO GROUND THE COIL TO THE DISTRIBUTOR BODY. If this ground path is corroded, dirty, spark can be lost.

An easy way to view actual parts for your vehicle, go to Rock Auto's website, plug the numbers in, and see the parts that fit what you are working on, that is the wan I confirmed the module type, and the identification you have given above in your post.

Coil testng should be done off the cap, on an electrical tester at a good parts store, let it run, get it to ops temp, that is usually where the failure process starts.

On the 7, and 8 pin EFI-HEI modules, same deal, run tester machine, but, only the HEI side of the modules can be tested, the EFI control section cannot.

Posts: 2

Reg: 07-09-19
07-12-19 05:44 AM - Post#2770520    
    In response to gchemist

Thank you

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