I have a problem with my 85 chevy truck, it ran fine and then I shut it off and when I went to restart it cranks but no fire. I have verified I have fuel and I have 12 volts to HEI bat/power terminal in key on mode and crank mode. the odd thing is it did this before and I let it sit for a couple weeks and then one day tested it and it started just fine. does this sound like a coil or module issue? I would assume since I am getting 12 volts switched during key events that the relay on the column is doing it's job..had to have the truck towed yesterday because of this and my free load of bricks ended up costing me $50
99% of the time with an hei, it's the module. The coils go bad very rarely. I've actually got a spare 4 prong in each of my hei equipped cars. Cheap insurance at $7.
I can tell you that the pick up coils can develop an intermittent open condition. The leads flex with the vacuum advance, and every so often, you get no spark. Sometimes, moving the leads around restores the spark, and the engine is fine until the next time. When this happened to me, I went through several module changes until I finally changed the P/U coil. Sometimes, I was able to get the engine to start by just repeatedly taking the cap off, moving the leads around, and putting the cap back on. Unfortunately, you must remove the distributor, then the gear to replace this part. https://www.rockauto.com/en/catalog...1052109,ignition,distributor+pickup+coil,7176
Modules don't go bad that often if you install them correctly. IMO, it's more often the P/U coil. Put an ohmmeter across the leads and move them around. Watch for any meter fluctuation. This problem made me nuts for about a year until I figured it out. Never left me stranded though as the car would start after I moved the wires around. It took multiple attempts at times, but It always worked.
What Larry said. I have seen pickup coils that would run when the vacuum advance was disconnected, but if the advance was operative, the instant that the advance kicked in the engine would quit. Ask me how I know...
Although I will agree with Larry and John that could be the issue, I'd spend less than 10 bucks and 10 minutes to give the module a try after I disconnected the vacuum advance as that's really fast and free.
I got to tell you I've been spoiled by Buick having their distributor up front all these years. Chevrolet stuff with the distributor at the back is a pain in the butt
Nah man I love putting my knees on sharp objects and dragging the top of my head across sharp objects hidden by nasty hood insulation
I agree, but bear in mind that simply changing the module involves moving the P/U wires around. Then when the engine starts, you figure that the problem is solved, until the next time.. Been there, done that, would have bought the tee shirt if there was one.
A quick check is to unplug the tach if it's equipped. I chased my tail with an intermittent no spark and it turned out the cheapo tach was grounding out the coil. The key to module life is a liberal amount of the supplied goop between the module and distributor. Most folks think it's dielectric grease but it's not. Use every drop in that tube!
OK, distributor has to come out. Knock out the roll pin and remove the gear. pull the shaft out. There is a small wire retainer that has to be pried out of a groove, and then the P/U coil comes out. This guy has some problems, but you get the idea.
That truck would get more than $300 around here. At least $350.00 Just kidding, very nice truck, and way more than $350.00
