1985 GM HEI ignition repair/upgrade?

Well, after being the truck that never needed anything, always there, always dependable, my '85 C30 refused to start over the weekend. The battery is well-charged and it cranks over quickly. No fire. I connected an inductive timing light to a spark plug lead, and it does not flash when the engine is cranked. It rained buckets the night before. Also, I noticed that one of my plug wires had grounded itself on the exhaust manifold. Was running less than a week ago, but might have been a little rough. I figure it's time for plugs and wires, cap and rotor, and perhaps the coil is shot? Module? Thoughts?

There is also pickup coil in there that could be bad. You have to disassemble the whole distributor to change that. I would probably consider buying a complete new distributor. I'm sure they can be had for under $100.

A common cause for no spark on mid 80s GM truck is failed spark control computer. There's a 4 pin plug that comes off of the distributor and goes through the firewall to the ESC unit. I started seeing them fail often way back in the late 80's and the ESC unit was high money even then. The budget fix is to unplug the 4 wire plug and permanently connect A to C on the distributor side.

did the C30 have a full electronic distributor by then, or did they still have the vacuum advance on the big trucks? i know there were some trucks that were a hybrid of the full electronic with the vacuum can on it, too..

but, based on what you say it does, i'm going to say that either there is no power to the "BAT" terminal on the cap from the ignition switch or the ignition module died.

There is a $15 module under the rotor that goes out. Could be that

Don't buy cheap parts. If you do, I will beat you with a stick selected from the finest hickory.

Anyway- HEI is really easy to diagnose, with a basic test light.

Big red wire- Has power with key on?

Remove distributor cap, look for hole burnt in middle of rotor. Look for carbon track from center contact on distributor cap to one of the coil mounting screws.

Remove rotor, tug on the two little wires coming off the pickup. They break.

If all appears correct, reinstall the rotor and cap, but take off the top coil cover. Have someone crank the engine, The three connectors up to will have power, ground and a flashing while cranking. No flashing, 90% you need a module. Flashing and no spark, either the coil is dead or its leaking off somewhere.

The above all presumes that its a non computer controlled unit, which I'd imagine, since its a 1 ton. If the module has 4 wires, its non. If it has 6 or so, its computer controlled. You can hook two of the wires together to make it run, but I forget which two wires. Its been a pretty long time.

If the bushings are worn, and the mechanical advance is seized, and etc, etc, the units that (I think) MSD sell for stock car crate motors are pretty robust, and quite reasonable priced.

http://www.smileysracing.com/shopping/?ic=1318

I'd buy #8365, but I don't trust cheap stuff.

Okay. I had some time to get into this today. I had forgotten what an unpleasant beast this thing is under the hood. Even with a small stepladder, the distributor is an uncomfortable distance back under there. The cap and rotor look good. There is power present on the "BATT" terminal with the key in the ON position. The coil tests good per the procedure in my shop manual. So, that pretty much leaves the module.

I'm hesitant to throw an entire aftermarket distributor at it, since such parts are almost never up to the quality of the OEM parts. I'll post an update when I get the new module installed. Thanks to all who've posted!

And for the record, distributor has mechanical AND vacuum advance. Two wires in the connector for BATT and TACH, and just three wires in the harness that runs from the module to the cap. Pretty sure this truck is not encumbered by anything so complicated as an ignition computer. It's pretty primitive, even by 1985 standards, and I like that!

Truly, I miss breaker points!

Back in the day, I used to carry a spare module in my tool bag. Used it 2 separate times to help stranded GM cars.

Well, I said I'd post an update, but I am not particularly proud of my diagnostic ability in this case. A new module did NOT produce the desired result. I believe a layer of iron oxide on my side post battery terminal bolts prevented my timing light from getting 12v. when I tested for spark. Spark is and was fine.

Further investigation revealed that the carb was dry. Fuel pump was not leaking. Lines were dry when I pulled the hoses. Installed new fuel pump. Cranked engine several times and no start. Cranked some more. No start. How long should it take the pump to fill the float bowl?

I pulled the line from the tank and applied 20psi air pressure to it. Could hear air escaping from tank filler neck. Reattached hoses, cranked engine, and it started almost immediately.

So, fuel line may have been obstructed. This is not the original gas tank, as the P.O. had replaced it, oh, maybe 20 years ago. Truck sits outside and doesn't get driven often. Tank may be full of rust.

1988RedT2 wrote: Well, I said I'd post an update, but I am not particularly proud of my diagnostic ability in this case. A new module did NOT produce the desired result. I believe a layer of iron oxide on my side post battery terminal bolts prevented my timing light from getting 12v. when I tested for spark. Spark is and was fine.

That's why you are supposed to get a friend to hang on to the spark plug wire as you crank it. Surefire test.

Fire with starting fluid or putting some gas down carb throat?

In reply to jfryjfry:

It's running now. But yes, I did pour a tad bit of gas into the carb. Would fire instantly, then die out, until I put air to the line. Then it started right up.