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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: fiddler on February 04, 2022, 06:46:34 PM
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I have a 1974 chevy C10 stepside. The engine is around a 1976 vintage 350. It has the hei ignition. I lost spark today. I had a load of wood on the truck and was heading 8 miles home when it died at a stop sign. Then it died momentarily on the freeway, but fired right back up. It kept kachunking up the last mile of hill getting to the house. When I got to the driveway it died 3 times while trying to position the truck to unload the wood. Now I have unloaded the wood and the ignition is totally non existent. I think my truck loves me. It waited to get home and the job done before it laid down.... That being said...I have a hot accel racing coil and wires on the rig just to ensure I got plenty of spark. I understand that the hot coil may be taking ignition modules. I don't race the truck and I was looking for reliability when installed that coil. Does anybody know 1) Do the hot coils in fact take out ignition control modules and 2) Is there a particular brand I should be looking for to get better reliability? So far the rest the components check good so I am pretty sure the ICM is gone again. This one lasted maybe 8000 miles.... I will go for parts tomorrow but may order them depending on response from you guys. I am also going to replace the coil with a standard stock level unit. Thanks much
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If it has the GM ACDelco HEI, replace with same parts. I had issues with the aftermarket modules until I replaced with the AC Delco parts.
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The issue with high output ignition coils is the increased current demand placed on the switching module. There is nothing wrong with installing a high-output coil as long as you install a higher current capacity module at the same time. Consider using a Pertronix Flamethrower III module or MSD module with your Accel coil. Personally, I would upgrade the entire distributor with a billet MSD plus MSD digital box or leave the ignition completely stock.
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So at this point the quick fix is to try the pertronix or msd module. In my heart I want to keep the high output coil. It just feels better to have hotter spark. The old girl starts and drives like a new truck most of the time so I want to not mess with what I have. If I lose the new module as well I will go back to stock at that time. Once more into the breech!! Thanks for your inputs. Always helps to share experience.
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If you are running a high output coil, you also need to run the matching carbon button, cap and rotor. You will melt a hole right in that bad boy. My advice is run a stock, readily available to you unit. When you are ready, update the entire ignition system.
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The coil, cap and rotor all came as one unit so they are matched. I thought I had all my bases covered, but did not know about the ICM. Thanks again all. I am supposed to receive the pertronix flamethrower III tomorrow.
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The high output coils sometimes take out the module when they fail. They may "test" on the ohm-meter just fine when cold but if taken up to temperature they layer short. Epoxy, that you and I can afford, HOLDS in heat. The best are the oil filled coils like the transformers you see on the electrical poles, but those are external from the cap. You'd need to do some wiring and build your own adapter to get it to work with HEI.
There is a guy floating around internet boards that explains it better than I can, IgnitionMan, or Dave Ray. If you google him, you can see some of his explanations of the problems with the HEI coil. He's been banned from a lot of forums, so you'll see that too. Doesn't make him wrong about the coil however.
The only thing I've ever really seen about the button is that high resistance ones CAN cause melting in the cap. Normally there's like a 5k ohms resistance button in a lot of cap and rotor kits, but MSD sells a low resistance one at 1k. The other pieces are usually brass and aluminum. I didn't measure a difference between the button in either one of those materials from Borg Warner's kits (both 5k), but I have heard the lower priced ones come with the low resistance already.
Those "high voltage" coils may deliver high voltage when they are cold but they drop off when they are hot. Plus they usually only deliver what is required to fire the plug, which may not be as much as you'd think.
My advice is if you want to keep the coil in cap is go stock style on the coil and module. The modules are VERY similar. There is supposedly a slight difference in the 996 modules, which the NAPA one is supposed to be a copy of, but you should always try to test the module before you leave the store.
The other thing to check is your grounds. A lot of these rigs have old rusty grounds and that can kill modules in a hurry too.
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I agree on the bad grounds being a majorly overlooked issue. This
but you should always try to test the module before you leave the store
won't do much of anything other than potentially wreck a new module. To your point about temperature affecting the dynamic operation of the coil, the same goes for the module which is an ESD sensitive component. Letting some parts jockey potentially send a lightning bolt through a new module is generally a bad idea. They are tested before they're boxed, so re-retesting by an incompetent is asking for trouble.
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Thanks for your help guys! OK so now I am in serious debug mode. I stuck in a pertroinix ICM and it lasted 5 miles. Thinking infant mortality I stuck in the msd ICM that i bought as a spare. It lasted to about half way down the driveway. Mind you I have an 800 foot driveway that goes down a hill, has hill and trees on either side, and is only 10 feet to 12 feet wide. So now the truck is blocking the driveway and i cant get the car out for parts. I live 12 miles from the nearest parts place and no transportation out here. So...I had the AC Delco ICM that I bought as a backup after the pertronix "failed" (Not Pertronix fault I think). I stuck that in and got the truck back to its parking place. NOW I will be replacing the coil, cap, rotor, condenser (you would think we could call them capacitors now, condenser in electronics went out way at the beginning of tubes), Stock parts, and a new AC DELCO ICM. Now...to the grounds....I have tested all grounds and they are lead resistance back to the battery.. About point one two ohms. I verified the voltage to the distributor and it is about .2 volts less than the battery to the negative battery terminal so that is good. I suspect the coil may have an issue that I can't see with a DVM. They are so hard to test without a hi pot..... I will just have to throw money at it....
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The "condenser" I think is to limit radio interference.
I would inspect the cap and rotor before replacement. Just stock style module and coil . . . .if it were me and I wanted to keep the coil in cap.
One single copper strand would probably show almost zero resistance, but when you're starting and running the ignition, it can pull a lot of juice. I would make sure there are clean connections on both the battery and where it connects to the engine.
I suspect it's the "super-duper" coil that failed and took out the module.
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The coil could be the culprit, but there are other things to consider.
Have you verified that the HEI coil ground strap is in place (attached images)?
Then, what convinced you that all of those modules are actually bad? Have you swapped one or more of the "bad" modules back into the distributor to see if it will fire, even for a short time? What about the pickup coil (PUC)? PUC failures are known to be intermittent and difficult to positively diagnose without a DMM and oscilloscope when not hard failures. See, Distributor components testing (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29995.msg251277#msg251277).
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So l have decided just to replace the distributor. By the time I got the stock coil and cap and rotor and cap cover and ICM I am looking at the price of a new distributor. Anybody got a favorite distributor to recommend??
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Rereading my replies here I do have one recommendation for an MSD distributor. I can't find a NEW AC DELCO so I am thinking a new MSD is going to last longer than a re-manufactured AC Delco. Thoughts?
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Sounds like your truck is sitting still over a bad pickup coil and you are blaming the module for it. Get one of those eBay special HEI's to stab in there and get back on the road again. Save up for a nice ignition system upgrade like an MSD.
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VileZambonie, I do not need to save up for an MSD ignition system, but I would like to know the ins and outs of what to get. There are a lot of MSD ignition systems out there. I don't need a racing system as I just use the truck to go to town for things that won't fit in the car, and I drive it to fiddle practice once a week so my wife isn't stuck without the car if she needs it. Maybe a trip to the dump once in while, pick up firewood, etc etc. I am looking for reliability. Also I like to do the wrenching now that I am retired and don't have to make it go today. So it would be cheap and "fun" to go ahead and try a pickup module. I have not tried putting one of the suspected bad ICMs back in the truck. I had a plate full of things to do today. The sun is shining and if that pasture gets ahead of me mowing it will be a nightmare. Best to keep it short before it becomes a fire danger..... Anyway, so you think an MSD unit would be a good upgrade? Any suggestions as to which one?
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Well, your post here has been confusing. You started out this post by saying you have a racing coil and are dabbling in performance parts for what sounds like a stock truck. You are saying you use the truck to putt around, meaning there is little to be gained from an MSD system. If that is all you are using the truck for then back to what I originally said, stock, readily available is what you want.
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I think there's been a little misunderstanding. . . . you mean you priced out the components of cap, rotor, coil, coil cover, and module you figured it was cheaper just to buy a whole complete distributor? I don't think you need to replace all of it. I don't think it's the failure of the pickup coil either, but maybe . . . .
there's a ton of info here: http://garage.grumpysperformance.com/index.php?threads/trouble-shooting-rebuilding-hei-ignitions.2798/
I'd start by checking the resistance of the pickup coil. The connector is to your right of the module as you are looking at it in the truck. Should be two wires going into the connector. When disconnected from the module, the module will have one smaller blade and a larger blade. Be careful pulling the connector because inside those wires like to move. Using an ohm meter check the resistance between the two wires. See if the reading stays when you wiggle the wires to make sure there is no break. Should be about 500 to 1500 ohms. There should be NO continuity between either wire and the distributor body. Make sure when reconnecting the module to the pickup coil connector that it makes a GOOD connection. I've been bitten by this a few times when I got no spark. Also verify that there's at least a little of the heat sink compound between the module and distributor. Not a lot, but some.
The cap and rotor can be checked visually for the most part. You're looking for any melted pieces or burned through marks. Along with making sure there's a ground strap as mentioned earlier, is to verify that you have the button in there correctly. From bottom to top, it's cap, button, rubber gasket and then coil. You can also check the resistance of the button at this time too. Should be 5k ohms or less. If the ground strap isn't there, there should be a new one in the package if you buy a new coil.
I think you can get by with a stock style coil and module. You could either hit the boneyard for a cap cover if you need one or get it from rock auto. I wouldn't necessarily get AC Delco, since they don't make anything anyway. Like I said, stock STYLE.
MSD makes some decent distributors that are for use with a box only but I believe you can also wire in a 4 pin HEI module to run them as well as a potential back up. But I think that's pretty overkill for your application. A decent stock system with .045 gapped plugs and some timing mods should put you right where you want to be. I'd still say external coil, but that mod is a little more involved than you may want to commit to.
Profom makes decent distributors, they make the GM ones I think for some of the crate motors.
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Thank you. When I got the truck it ran so badly that I wanted a good reliable strong spark so I did not have ignition issues to deal with so upgraded the ignition when I replaced it. That said I don't think I have 15000 miles on this ignition setup. Turns out the carburetor was toast and I had a myriad of vacuum leaks. It was frustrating because as I found a vacuum leak there was another one going on so as I fixed one after another the truck didn't run better. I plugged the brake booster line suspecting the sighing of the booster might indicate a vacuum leak and nothing got better so I dismissed that one Took awhile to get back to it and then discover that I was running manual brakes and the thing was leaking vacuum all the time. Anyway since all of that is fixed the truck runs like new and drives like new. Also the truck has a edelbrock 1406 carburetor and edelbrock manifold so it kind of seemed like I should have the better ignition system... I am going to do some more debug today. Maybe give it one last run and drive it around the pasture for awhile before I put it out on the driveway... I can work on it in the pasture if she dies on me again....Maybe get a backup distributor to carry with me LOL...
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So to lessen the chance of being stranded out on the road and needing another tow I decided to replace that distributor. It was actually at least as easy as replacing the ICM! I got a MSD Streetfire from Amazon with my prime membership for 201 plus tax...no shipping charge. It was in Mondays mail and I still don't have the parts I ordered to fix the old one. I had a full plate yesterday so I did not get around to installation until today. That has to be the easiest distributor installation I have ever done.... Anyway.. is it necessary to install the vacuum advance stop for a stock engine or is that a racing thing?? Or would you guys even use a vacuum advance on a racing engine?
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So the vacuum advance stop was necessary. After an initial run up the driveway, (aggressive climb) indicated I was going to have pre ignition problems I installed the stop on position A. No more ping. It sounds different. I think maybe there was a hint of a misfire happening on the old ignition setup. Maybe that coil was breaking down and taking ICMs with it. Anyway...Thanks for all of the suggestions.
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Do you have a timing light? Did the distributor come with extra springs to help tune? Is the vacuum advance adjustable with an allen key?
I think you'd be happier with a faster mechanical advance, less advance from the vacuum and adjusting the rate of the vacuum can.