HEI Problem Question

[Robert Crandall]

I am looking for help on a fix for a problem with the HEI system on a 1978 C20 292 I6 2WD 4Spd.

This truck will not start on occasion. The problem has existed for more than 10 years now. Early on I went through the steps in the repair manual, and I replaced everything in the distributor. The distributor was bought as a rebuild some time before the problem began, and I have not bought another one since the problem started.

After a few years the fix was found to be: Unplug the connection to the HEI module within the distributor, wait approximately 1 minute, reconnect the plug. The truck will then start immediately.

The truck runs perfectly. This problem is causing no driveability issues. It starts without problem when left for only a short time, like to go into a store. When the problem occurs, it has been left for at least 4 hours. It is random. It may happen every time it has been left for a few hours for 10 times in a row, and it may not happen at all for a month. It seems to be completely random.

I have not been able to find an answer to this problem. Does anyone know how to fix this?

[Axle]

I'd take out the condensor and see if it'll fire. (you will want to replace it with a new one if it works).

Alex.

[craig113]

Check for good grounds between block and frame, cab.

[Just call me Sean]

Those parts store modules aren't that great. I would try a new one, especially since unplugging it yields results.

[Oregoon]

Originally Posted by Just call me Sean

Those parts store modules aren't that great. I would try a new one, especially since unplugging it yields results.

Seconded. I went through several cheapos before finally getting a good one. I think I sprung for a Mallory, and it gave me no more issues.

My last truck did the same thing, though after it would randomly fail, it would never start again until I got another module.

[Robert Crandall]

Thanks for the suggestions. I do have good grounds, at least as shown on the meter. It makes no difference which manufacturer's module I use. One of them is an AC Delco OEM. I have many in the collection of them that I built up before I learned that unplugging it for around a minute gets me going again. My guess is that something needs a minute to either charge up or discharge down. I have been more than 10 years on this. The only thing within the distributor that I have not changed is the condenser (or whatever it is that looks like a condenser) which I am told is not available separately from a new distributor.

[greg64]

When you say you're disconnecting the module for a minute, is it the pickup side or the coil side you're disconnecting? Might tell us something more about the problem. I'll second (or third) the idea that some modules are bad.

[Robert Crandall]

I do not know. It has been some years since I actually looked at it. I will get a picture, but that will be tomorrow evening at the earliest. The motor is a 292, so the distributor is easily reached while standing in front of the truck. With one hand I hold the cap a little up and off toward the back of the motor with its front edge sitting on the rotor. This makes the module visible under the rotor. A screwdriver will separate a plug that contains a green and a white wire. I can then reach it and finish removing it from the tabs on the end of the module that is next to the motor without having to remove the rotor. About 1 minute later I then reinstall that connection then the cap, and the truck starts immediately. I keep one screwdriver and a flashlight on the floor in front of the seat for this task.

[Robert Crandall]

I forgot that I was going to be home for a while this afternoon. Here are two pictures of the subject distributor lifted to where I can unplug then replug the module connection.

[mrolds88]

Had a similar issue with a 350. Replaced everything at least once. Finally replaced the distributor. Had the same problems, IE starting when it wanted. Turns out that the terminal on the coil power wire was worn and would connect and disconnect at will. Slipped the brass terminal out of the plastic, crimped it down a bit and the world got to be a little better place.

[Robert Crandall]

Nice! This is something that I have not yet looked at. It will take me a while to find out which connection that you refer to, but I will have a look. If I cannot find it, then I can crimp all that I find. There are not that many. Thanks.

[ron350]

Robert the condenser part number comes up as AC Delco D211.
http://www.rockauto.com/catalog/x,ca...,parttype,7092
The condenser is there for radio noise suppression and reads .25uF to .40uF and can only cause problems if it shorts to ground.

I am curios why unplugging and replugging the pick-up coil from the ignition module causes the ignition to work again?

If I remember correctly the vacuum advance would cause the green wire to break inside the insulation on the factory pick-up coils.
http://www.rockauto.com/catalog/x,ca...,parttype,7176

You may be loosing 12 volts from the ignition switch to the HEI.
This is a red wire that plugs into the HEI that can have a loose connection.
Mrolds88 describes repairing a loose wire to clip inside the plastic plug in post #10 above in this thread.

When HEI’s came out I had a cousin that worked at a Chevy dealership as a line mechanic. When he came across a problem like yours he would clean the ground connections and add a long braided copper ground strap from the frame to a transmission bolt. I can remember the ground straps came in a long thick paper envelope with the GM part number printed on it.
On all of my cousins GM vehicles he had a ground strap running from the head to the firewall on both sides of the motor and one frame to transmission bolt ground strap.

[Robert Crandall]

Thanks for that advice. I see that the pickup part has the connection that I unplug then replug. I do not know why unplugging then replugging works, but I am glad that it does because it allows this truck to remain in service. I just eventually stumbled onto that fix after a few years. One of the schemes that I came up with over the years was to run a wire from the battery connection at the starter to a switch in the cab then to the distributor. That worked fine. I had to turn that switch on before I started the motor then be reminded when I turned the key off that I then also had to turn that switch off. It made no difference on this HEI problem.

[mrolds88]

Robert, the wire I am talking about is the red one that clips into the distributor cap. That is the one I had issue with.

[greg64]

Robert, thanks for the pics. So you're disconnecting the pickup that triggers the module. The signal present there is quite small, and smaller still when cranking (low speed). I'll bet there's a bad connection in there, or as the previous poster stated, the wire is broken inside the insulation.

[Robert Crandall]

I changed the coil pickup today. That is a part that I have not yet changed. It would be nice if this is the one. Time will tell if it is now fixed.

Thanks for the advice on changing this part.

[gmachinz]

I also drill a small hole on the dist. base along the side and use a 7mm self tapping seraded machine screw to attach a 12ga ground wire from there to chassis using a grounding ring-along with ringlet are two grounds from each side of the rear of the cylinder heads. I used to do this on all of my performance builds-providing a better path to ground helps maintain a cooler control module.

[RPOZ11]

Originally Posted by gmachinz

I also drill a small hole on the dist. base along the side and use a 7mm self tapping seraded machine screw to attach a 12ga ground wire from there to chassis using a grounding ring-along with ringlet are two grounds from each side of the rear of the cylinder heads. I used to do this on all of my performance builds-providing a better path to ground helps maintain a cooler control module.

Got any pic of this
I'd like to see what that looks like