HEI distributor problems
 

I've been fighting a HEI problem ever since I've had my 68 C10 done. I bought a new AC Delco distributor when I built the 350. I have a AAW wiring kit installed so I've got the correct wire to the distributor.
About every 2 or 3 thousand miles I loose fire at the distributor. I've replaced the module each time, I've gone through 4 or 5, and the truck'll start right up and run fine till it decides not to start again. My question is is there something in the distributor that can be causing the modules to go bad? I replaced the coil with one off the shelf, didn't help. I just ordered a new DUI distributor from Summit out of frustration. Any and all help or advice is welcomed.

Re: HEI distributor problems
 

Possible grounding wire underneath the 2 screw plastic coil cap is missing

Re: HEI distributor problems
 

Possible improper voltage during startup, this can slowly kill an HEI module. Good idea to double check it so you can cross it off your list if it checks out.

Re: HEI distributor problems
 

Do you still have an external voltage regulator charging system? The modules in the HEI distributor do not like voltage spikes and the external regulators have been suspected to be the cause of module failures because they do not do as good a job of keeping the voltage in the circuit at a constant value.

Re: HEI distributor problems
 

Just got in from the shop and here's what I've found.
KWMech, yes ground wire at the coil is attached.
SouthCity, voltage at the distributor is 12V with key on, 9V when cranking engine, and 13.8-9V running.
VetteVet, I have a one wire alt. 100Amp Powermaster.
One thing I noticed when I tested voltage while running was the voltage would drop to 4 or 2V just for a millisecond and the be right back to 13.8. I checked the running voltage at both the distributor plug and at the fuse panel bulk head connector at the firewall. Wiring is new AAWclassic update for HEI and one wire alt.

Re: HEI distributor problems
 

Ground wire INSIDE the coil

Re: HEI distributor problems
 

Yes I pulled the plastic cap off the coil and the ground wire is attached to one of the screws that hold the coil in.

Re: HEI distributor problems
 

Engine block to frame ground, frame to body, battery to body. Check them all. I've run HEIs for years with original alternator without any problems. My 68 still has the original alternator and regulator on it

Re: HEI distributor problems
 

Yes my grounds are from the battery to the front of engine block, rear of engine block to frame and from the frame to the cab.
I'm using the starter positive post to pick up power to the cab instead of running a separate wire from a junction block beside of the battery as was factory. I don't think that would cause the problem. Sure has got me stumped, I'm leaning to a glitch in the distributor itself.
As far as the voltage dropping to 9V at the distributor when cranking is that because of starter drain?

Re: HEI distributor problems
 

I'm surprised nobody has asked what you are using under the module to goo it down, if you're using heat sink compound.

Re: HEI distributor problems
 

2nd on the heat sink question.

What is your plug gap? Normal HEI is .045. Early ones had special plugs and .060 but I think they went to .045 as a more reliable gap.

Re: HEI distributor problems
 

Yep I bought a tube of the heat sink compound and have used it underneath each module I've changed
Plugs are gaped at .045

Re: HEI distributor problems
 

Well if your new DUI distributor starts getting failed modules, I would next suspect the alternator and aim to put a 3 wire internally regulated one on the truck, with the sense wire connected at a junction away from the alternator (not just connected on the big post of the alternator with a few inches of wire). I have also seen really weird things happen in vehicles due to a battery that is failing but still cranks and works in the vehicle for a couple more years. I have not seen distributor module failure due to that, but it would not surprise me. I do wonder about your short duration voltage drops to 2 or 4 volts, and about the dropping to 9v during cranking. Do you have electric fans on the radiator?

Re: HEI distributor problems
 

No electric fans or AC or any extra power accessories. I don't even have a radio. As far as the alt. the wiring harness was designed for that type. I'm going to give AAW a call to see if they can steer me in the right direction on the voltage drop issues.
Thanks to all you guys who have given insight to my predicament. If I get a concrete answer I'll let every one know.

Re: HEI distributor problems
 

sub'd

Re: HEI distributor problems
 

Check the Pickup coil in the bottom of the distributor for bad wires, signs of heat and shorting.

Re: HEI distributor problems
 

Got my new DUI distributor today but won't be able to get it installed till the first of the week. Our new pergola kit for the patio arrived today also so you guys probably know which one I'll be working on for the next couple of days. LOL

Re: HEI distributor problems
 

I'll check the old distributor when I pull it.

Re: HEI distributor problems
 

What kind of tube? Not all are the same

Re: HEI distributor problems
 

Super Lube silicone heat sink compound. Bought it at Auto Zone

Re: HEI distributor problems
 

Do you have anything connected to the solenoid "R" terminal?

Re: HEI distributor problems
 

No my starter doesn't have a R terminal.
I talked to AAW about the voltage drop to 9 V when cranking and they said that's normal. I put a new battery in Fri and when running the voltage at the distributor is a constant 13.8.

Re: HEI distributor problems
 

So there has been no changes to the charging system during all these failures?
If so have you checked the alternator output for AC voltage? If the diode bank in the alternator is failing AC voltage could be spiking the modules and causing the failures.
This one of those times an oscilloscope is handy.

Re: HEI distributor problems
 

>>Super Lube silicone heat sink compound. Bought it at Auto Zone<<

I looked at the Autozone web page to see what Super Lube product you are using. I couldn't find it there, but I assume the image below is the product you are talking about.

A Dielectric is the exact opposite of a heat sink compound so I don't think Super Lube knows what they are selling. A Dielectric is an insulator.

I would not use that product. You need a thermal grease, thermal paste, thermal compound, CPU grease, heat paste, heat sink paste, or thermal interface material, but not one that says dielectric.

The last couple of HEI modules I have bought, came with a small individual application packet. Those packets are unlabeled, but I used them. I assume Accel knows what they are providing. I still have a small tube from Radio Shack, but next time I'll probably get a CPU grease from some place like Best Buy.
Don't be confused by a product that can handle high heat. You need a product that can transfer heat.

>> I noticed when I tested voltage while running was the voltage would drop to 4 or 2V just for a millisecond and the be right back to 13.8. I checked the running voltage at both the distributor plug and at the fuse panel bulk head connector at the firewall.<<

Do you get that 4V at the Alt Bat terminal?

The 13.8 is at idle? What is the Alt bat terminal voltage at idle and with the engine held at 15-2k rpm for a full minute?

I'd loose that 1-wire Alt.

Re: HEI distributor problems
 

HO455 you lost me when you spoke of AC voltage. How do you check AC voltage with the VOM?