Engine is a Chevy 250. I installed an eBay special GM HEI distributor about 25 years ago. Within about a month, the no-name offshore module died, so I installed a genuine Wells module and it has worked flawlessly for the past quarter century, until... A few weeks ago, as spring weather peeked out from behind the rain, I drove the truck to run a few local errands. On the way home (at about mile 10 of my trip), the truck died. I hit the starter and it was obviously not getting spark. I don't have a lot of people in my area to lean on, so I called Hagerty to exercise my towing benefit. So, an hour later, my truck made it the last 2 miles home on the back of a flatbed. I did some basic diagnostics-- confirming 12v to the coil, confirming no spark at the plug... so I ordered a genuine AC Delco module... and while I was in there, I figured I might as well throw in a rotor and condenser assembly... for the new wires and molex plug. All of these parts were genuine AC Delco. When they arrived, I installed the parts, including adequate and appropriate amount of thermal paste, and the truck fired right up. Yay. Easy fix. Until I went on a short drive a few days later. Same problem as before. The truck died, spinning the engine it was clear there was no spark. So, another call to Hagerty, this time to flatbed tow me less than 1/4 mile to my house (I live in a very hilly area, I can barely walk... I couldn't push it if my life depended on it). So, now we've moved into the "throw parts at it" phase, which can get expensive at $45/module (and wondering when Hagerty is going to balk at towing me again). I installed another genuine AC Delco module with adequate and appropriate thermal paste and, since I actually had a spare, a brand new yellow wire coil, button, and leads. Truck fired right up. Yay! Fixed again. I have started it a dozen times since, and let it run for as much as 20 minutes, just burning up gas in the garage... no misses, no burned up modules. However, I'm gun-shy about actually driving it now. Aside from fearing Hagerty's ire, getting stranded for an extended period can have a pretty big toll on my chronic health issues. I'd really like to know if I've actually fixed it. Again, this truck has been immensely reliable for 25+ years... firing up on demand without issue. Then, in the course of a couple of weeks (10-12 total miles), 2 modules dead-- one genuine Wells, and one brand new genuine AC Delco. Alternator puts out 14.7v at the terminal. Battery voltage is 12.4. Key-on voltage to BAT terminal on distributor is 12.4. Ground continuity from battery to engine block is rock solid at 0 ohms. I also buzzed the old coil (MSD 8225 yellow wire) but I don't have the numbers handy... they were all 'good' ... no shorts, 10k or so ohms across BAT and button, etc. What next? And before someone suggests I swap it back to points... thanks. But the GM HEI ignition was installed in umpteen bazillion vehicles and proven itself to be at least as reliable as their points ignition predecessors. I'm trying to fix what I've got.
Silicon dielectric grease is an insulator. You need the white thermal conducting paste. I’ve seen many modules fail because of not using it. NAPA used to carry it in small tubes.
Underneath the coil is a metal grounding strap. It is very easy to overlook when you replace the cap or coil. If it is left out the car will run for a short time before it dies.
A common issue on GM HEI system was the wires at the pick up flex every time the advance pulls on the pick up and the wires would break but still be inside the covering. Pretty common back in the day.
The HEI is pretty simple, reliable and self contained. That's why they are so popular. Typical issues are the module getting fried, the wiring breaking, arcing thru the cap and rotor due to the high ouput and poor voltage supply. You have replaced parts, confirmed voltage and ground. So the typical problems are not showing. At this point, I'd look at the pickup signal. This was an issue on the V6 variant, especially in Fieros, not so much on the earlier big cap 6 and V8, but the basics have been covered and you have checked input, replaced both coil and module, so it's the last part of the system. The White paste between the module and dist. body is very important, lacking this will cause modules to fry. I'd keep a test light handy for any test drives and check what you see at each of the wires on the body to cap harness when it's running (B+, tach, ground). If it dies again, this will help diagnose it. Most likely, it will lose tach (pulse when running). EDIT: You can run the engine without the coil cover on. First, it holds the connectors down, so make sure to make the connections and have them all fully seated in the connectors. Second, you can/will get zapped if you touch the connections, so exercise caution, but they can be probed with a test light easily with the cover off. Of course, don't short from one connection to another.
I had an issue one time that we tracked to the alternator but you have already checked that so that’s good. The basics have been covered. I how ever have had two modules for same exact said engine that were bad. And yea they were Delco parts. I went to DUI. And told them what I had and that I was tired of it. They sent me everything they had but the housing. Nylon bolts /their coil /etc/etc/etc. that was in 2003 when the first issue of what has been called lost boy to me. It has never missed a beat. And that was in a racing environment. It will fire .050 gaps /and with a blower. I am running solid copper core wires for obvious reasons. I would buy from them again in a heart beat.
Wrong terminology on my part. I used the paste provided with each of the _3_ different modules-- the Wells module I installed 25+ years ago, and the 2 AC Delco modules I've installed in the last few weeks.
Unfortunately, the AC Delco modules of today, manufactured offshore, are not the same quality as the US made modules of 25 years ago. I have been buying the 4 pin GM HEI modules from NAPA. They have two different part numbers available. I have tried both. They are not indestructible, but they have a five year guarantee, and I've had no problems getting them to give me a replacement. I do carry an extra at all times. I hope this helps.
Understood on the reduced quality of modern replacement parts, but the problem seems to span brands... perfectly working Wells dies (perhaps it just decided to die after 25 years, who knows?), then AC Delco dies after only a few miles. I clearly am out of ideas, but using basic root cause analysis rules, 2 deaths within days (literally a few miles apart) from differently brand parts lends probability away from brand being the problem. Of course, 2 datapoints is small, so it doesn't fully rule out the possibility that the brand new AC Delco was just crap and died. At this point, given my personal life circumstances, I'm now too worried to be able to enjoy just driving it *sigh* For the thread generally, some additional "info" I gathered over last few weeks... I did previously call DUI (I'm using a fancy set of their wires) because they've always been approachable. But they didn't have any real suggestions beyond all that I had already done. I also called Tom Lowe at 12bolt (he built the engine), who said it was the coil. Maybe it was, maybe not. It hasn't died since I installed the latest module and new coil, though 1) not failing yet doesn't mean the problem is solved, 2) I haven't found anything out of character about the old coil-- no cracks in bobbin that might cause wire annealing to chafe and short, leads are solidly connected, etc., and 3) coils aren't really a "wear" item. And, finally, I called Pertronix (also, because their support people have always been very approachable)... who told me I probably had a bad ground, which doesn't seem to be the case based on my measurements. So, following basic RCA steps, it worked a really long time, then failed at x. Replaced x. It failed again at x. This points to something new causing x to fail. What's the something new??? My hair is too short to pull out properly at this point. Thanks, all. Please keep the ideas coming.
I'm leaning toward poorly manufactured modules, but I will follow along to see what you learn. How many miles per year do you use your truck? I've put 46k miles on my rod since switching from Pertronix to HEI, in 2015(?). The modules seem to last 2 to 3 years. The indication I have that failure is coming is ever increasing crank times before firing, especially when the engine is at operating temperature.
There are only three components that would do what you describe. The coil, module and the pick up. Unless there is a problem with the power supply circuit.
< 1000 miles/year. I start it up every 2-3 weeks and let it run to warm just to keep everything lubed (and to listen to the exhaust). In the case of both the 25+ year old Wells and the first AC Delco, there was no "impending failure" clue. They worked flawlessly, then were dead as a doornail.
[QUOTE) I did previously call DUI (I'm using a fancy set of their wires) because they've always been approachable. But they didn't have any real suggestions beyond all that I had already done. I also called Tom Lowe at 12bolt (he built the engine), who said it was the coil. Maybe it was, maybe not. Thanks, all. Please keep the ideas coming.[/QUOTE] I just came upon this post and was thinking it might be the coil also. I had the problem years ago on a 72 Dodge. Engine kept dying, no spark. After a cool down it would start right up. Noticed the coil was extremely hot to touch.( might of been oil filled, I can’t remember) Was the new coil in the car when you tried idling it for 20 mins? You might try a few of the old modules to see if they work now. Worth a shot for piece of mind.
The best test for the pick up is to give a slight tug on the wires and see if they pull out of the reluctor ring.
Decades ago when we ran a AMOCO station we had a tester like this one put out with STANDARD OIL on it . It allowed you to test all the components. But back then the large oil companies were big into auto service. I don't know of a way to test the pick up otherwise. https://www.ebay.com/itm/1263861674...wBufVhzOUVAvKePCXrivWJlkzw==|tkp:BFBMytmnt-1j
Had a V8 powered S-10 pickup that someone prior had tried to add trailer light wiring to and had made a birdnest out of it. Started blowing taillight fuses about once a week. At the same time the truck was killing ignition modules about once every two to three months. I never connected the problems until i found an unmolested rear light harness and plugged it in. Quit blowing fuses and i never replaced the ignition module again for years. Coincidence? Maybe. Anyway, if you have any other intermittent electrical gremlins you may look into fixing them.
I couldn't find the original Wells. The AC Delco #1 is DEAD DEAD. Swapped it in, no start. Swapped AC Delco #2 back in, started right up.
I've been through the same with my C10. Think about it like this. There are only a few things that affect the HEI, heat (all of them have to tolerate that), grounding and the charging system. I have had 2 vehicles with repeated HEI failure and all were fixed by replacing the alternator. As the diodes in the alternator get older, they start to leak AC into the circuit and HEI does not tolerate AC. Verify that your distributor only has about .2 ohms beween the negative post of the battery and the distributor housing. Then, get a quality rebuilt alternator and I will bet your problem goes away.
I addressed both points in my OP. Alternator is putting out a steady 14.7v. That's using my DVM at alternator terminal and grounded to support bracket. Now, I can't say how noisy that 14.7v is coming out of the alternator, but the voltage at the meter doesn't bounce around. Ground continuity is zero ohms of resistance from bolt on the block to battery negative. I have also confirmed at base of distributor and from same alternator bracket mentioned above, as well as checks to motor mount saddles, fender bolt, etc. Ground is good.
Continuity uses milliamps to check. Try doing a voltage drop while cranking to be sure. Read voltage between the block (+) and the negative battery post (-). Should be very close to zero. Not saying you are wrong, this is just a better check.
Good idea for cross-checking the DVM. I just tested v drop, and for the 1 second of crank before the engine fires, I'm seeing 0.2v... which is about what I expected. As soon as key springs back to run position, voltage goes to zero. Also as expected. I hate to beat this thread like a dead horse, but it would be nice to find something to hang root cause on before I try driving down the hill again. I just fired it up and let it run for another 15+ minutes, and it fired off instantly, and ran great. Gratuitous sound file attached.
Glad that checked. I will mention something we are all used to in computer/consumer electronics which may apply to this; It fails right away or not at all. That doesn't explain why Delco #2 is back to working. Insert shrug.
Can you elaborate? I'm getting a solid 12v to BAT terminal on distributor with key in run and start positions, zero when off. When I hit the key, the starter spins right up... no hiccups or "iffy connection" sounds.
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