Posted: 12/3/2016 9:00:31 AM EDT
| The shop I manage works on European automobiles, so I am used to 80's and later fuel injected Euro although I do work on the sporadic air cooled Beetle. I personally have a Chevrolet C10 that my dad bought brand new, and he gave me a few years ago after he quit driving it (it was one of his favorite vehicles and he never traded it). I drive it periodically to work and around town, but it gives me some type of problem that needs fixed about every 3 months. It started life with the sucky 2-bolt main 305 that it made it's first 120k miles with, my dad had rebuilt and drove until the head gaskets pooped after another 20K miles and he stuck a 300hp GM performance 350 in it about 2001. It currently has 174K miles on it, around 30K on the engine itself. Great engine, but we have kept the Quadrajet (it's wearing a Summit rebuilt Q-Jet on it now) to keep originality on the new intake that came with the crate engine. I think he recycled the old 305 distributor or at least swapped it to a used one off a 350 - he doesn't remember. I put plugs, wires, MSD rotor, cap, and coil on it three or four years ago. Before I put the coil, cap, and rotor on it, it would "hiccup" but not die after driving about 45 minutes. That went away completely. It has been gone since, but I was driving it to work Wednesday morning (about 40 degrees but higher humidity because it had just got through raining for 3 days) and it completely died going about 70mph down the interstate. This was after it had been running about 15 minutes. I was three miles from work, and it died as if I cut the ignition off. It would crank over but not even try to hit a lick. I had to give up after a few minutes of cranking, and have it towed. An hour after it quit, it still would not start. Another 2 hours later, it started right up. Now anytime I try it it starts and runs perfectly but I have not got out and driven it because I suspect it will stop again and there is no where near my shop that I trust leaving a C10 on the side of the road waiting three hours for it to start. It is at the shop, so I have my tools, timing light, etc. I am trying to decide if I want to 1) proactively replace the entire distributor with one of the inexpensive new ones that is about $120 wholesale (I have that option working in the business or 2) let it sit and run and hope it will eventually get warm enough to quit and use my timing light to see if I am losing spark as I suspect it did because it was a sudden stoppage with no sputtering and didn't attempt to even hit once while it was still warm. I don't like putting parts on that I don't need - it is a policy as a technician that I try to duplicate all issues before condemning a part to stop comebacks in the shop. However, the distributor is a b*^%ch to get to a 350 and it is HEI so I don't think it will be easy to put an oscilloscope on the reductor to see if it is picking up distributor rotation and then put a meter on the module and see if it sending 12v signal to the coil to fire. If this was a distributor type Mercedes, it would be easy but the compactness of the GM distributor design makes it tough, and it is stuck at the back of the engine in a truck. I don't want to be lazy but I also don't want to waste my time if I just need to put a distributor in and be done. This is a "hobby" vehicle for me, not primary transportation so I have time to work on it. What sayeth the SBC saavy members of the Hive? |
| I had this happen to me on an old 78 k20 I had with a 350, it would die or stall out at random times for no reason. There is a small fuel filter in the carb itself where the fuel supply comes in if I remeber correctly(this was 8+ years ago and 20+ trucks) I removed that filter and it was loaded with crud, once replaced ran great no issues, worth a shot to check that before spending all kinds of money replacing other stuff. |
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Had this happen on my old 79 caprice.
The diaphragm on the mechanical fuel pump was going bad. Was hit or miss for a couple weeks then went out completely. I replaced the fuel filter, distributer cap, plug wires, and battery wires trying to track it down thinking it was likely electronic. The engine mounted mechanical fuel pumps are easy and cheap to replace but don't have the life of the in tank electronic ones. |
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Some of the older ignition parts can crack and they run fine until they get hot. I don't recall exactly what part. coil or condenser or ? A bad electronic ignition module will do this, get hot and shut off and not restart until it cools. You can pull it and have it tested at autozone. |
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Check to make sure you're getting good fuel pressure. It may be a weak fuel pump. You probably have the old original mechanical diaphragm type pump on there. Go thru the fuel system, make sure the carb is not gunked up, needles are good and not bent and any clogging inside the carb. If you don't have fuel filter on the system you need to put an inline fuel filer on it.
Second, |
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Long shot guess from an old man's gray matter....
Early 80's GM products had/have an issue with some of the electrical connectors. Seems like the male end of the connector is metrical & the female was SAE. Over time a thin layer of corrosion builds up between the larger females and small male connector cause frustraining  very intermittent misconnectable flowing of electrons.  You may have a hot dog down a hall way problem.
Check for low fuel pressure or plugged fuel tank vent too. Engrish is our Second Langrige Custom Autowerks.™ |
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My long range diagnosis is a bad ignition coil or a loose connection at the coil or condenser. After that check fuel flow since it is easy. A failing coil is a nightmare. Ran into the same problems as the OP. 2 days of screwing around to find the culprit. |
| Thanks for all the input guys. I didn't put more information in the original post to keep from being too much of a TLDR. I know it's not a fuel issue, they will almost always sputter as you should have a bowl with some amount of fuel in it until the bowl runs outs and it gets low and it starts going lean before hand. I put a new Delco mechanical pump on last year after the old one sprung a leak where the body cracked. I put a new filter in it a couple months ago as the check valve on the filter gave out and it took long cranks to pump the bowl back with sufficient fuel to be picked up by the jets. I will pull the cap today (it's at work not at home) and check everything and pull the module and have it tested. I have Advance/Carquest (we use the Carquest which is now Advance Commercial), O'Reilly and Auto Zone within a block of one another near the shop. If it was a German car I would have figured this out in minutes. I even diagnosed a 1978 Porsche 911 pretty easily the other day - it uses 400V AC instead of a 12V DC to fire to coil, easy to put an O-Scope on the coil wire and find a sine wave but only 6 volts, and was able to test the wire from the reluctor in the distributor to the Bosch module to see signal there. It's just a pain to get to and a little unfamiliar to me on the Chevy. There is nothing more expensive than a free vehicle. I tell my customers that, and it rings true for the mechanic as well. I am working on this, just bought a 1986 Alfa Romeo Spider that runs and drives but the manual transmission pours trans fluid out of the input shaft and two of the brake calipers are seizing up. That's why I like guns more than cars, although I do love cars. You can oil a gun and put it in the safe for a year and it's still the same when you pull it out. Park a car for three months and something is going to be wrong when you go to start it, and if not, will be in a few days. |
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Just replace the whole distributor. It's cheap and has a new pick up coil.
I am betting on the ignition control module. If going with just that part only get a real GM one. Some have thermal paste to transfer heat, the new ones come with die electric grease which is not the same thing. I was into fieros as you can see my avatar and I had one cook off myself. Always carried a spare and tools to swap. |
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The shop I manage works on European automobiles, so I am used to 80's and later fuel injected Euro although I do work on the sporadic air cooled Beetle. I personally have a Chevrolet C10 that my dad bought brand new, and he gave me a few years ago after he quit driving it (it was one of his favorite vehicles and he never traded it). I drive it periodically to work and around town, but it gives me some type of problem that needs fixed about every 3 months. It started life with the sucky 2-bolt main 305 that it made it's first 120k miles with, my dad had rebuilt and drove until the head gaskets pooped after another 20K miles and he stuck a 300hp GM performance 350 in it about 2001. It currently has 174K miles on it, around 30K on the engine itself. Great engine, but we have kept the Quadrajet (it's wearing a Summit rebuilt Q-Jet on it now) to keep originality on the new intake that came with the crate engine. I think he recycled the old 305 distributor or at least swapped it to a used one off a 350 - he doesn't remember. I put plugs, wires, MSD rotor, cap, and coil on it three or four years ago. Before I put the coil, cap, and rotor on it, it would "hiccup" but not die after driving about 45 minutes. That went away completely. It has been gone since, but I was driving it to work Wednesday morning (about 40 degrees but higher humidity because it had just got through raining for 3 days) and it completely died going about 70mph down the interstate. This was after it had been running about 15 minutes. I was three miles from work, and it died as if I cut the ignition off. It would crank over but not even try to hit a lick. I had to give up after a few minutes of cranking, and have it towed. An hour after it quit, it still would not start. Another 2 hours later, it started right up. Now anytime I try it it starts and runs perfectly but I have not got out and driven it because I suspect it will stop again and there is no where near my shop that I trust leaving a C10 on the side of the road waiting three hours for it to start. It is at the shop, so I have my tools, timing light, etc. I am trying to decide if I want to 1) proactively replace the entire distributor with one of the inexpensive new ones that is about $120 wholesale (I have that option working in the business or 2) let it sit and run and hope it will eventually get warm enough to quit and use my timing light to see if I am losing spark as I suspect it did because it was a sudden stoppage with no sputtering and didn't attempt to even hit once while it was still warm. I don't like putting parts on that I don't need - it is a policy as a technician that I try to duplicate all issues before condemning a part to stop comebacks in the shop. However, the distributor is a b*^%ch to get to a 350 and it is HEI so I don't think it will be easy to put an oscilloscope on the reductor to see if it is picking up distributor rotation and then put a meter on the module and see if it sending 12v signal to the coil to fire. If this was a distributor type Mercedes, it would be easy but the compactness of the GM distributor design makes it tough, and it is stuck at the back of the engine in a truck. I don't want to be lazy but I also don't want to waste my time if I just need to put a distributor in and be done. This is a "hobby" vehicle for me, not primary transportation so I have time to work on it. What sayeth the SBC saavy members of the Hive? Pick up coil in the distributor getting heat soaked |
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HEI module, keep a spare in the glove box It can also be the pickup coil..OP, put a mighty vac on the distributor advance can and with it idling add/remove vac....if it stumbles or dies most likely a pickup coil wire is broken...you can also pull the cap, unplug the wire connector off the module and test with an ohm meter while wiggling the wires....most likely cheaper to just go pick up a rebuilt distributor from Napa and swap...... |
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A sudden stoppage is going to almost definitely ignition related.. Likely a loose wire or a bad ignition switch. There really is only a few wires to look through on an HEI system.
Ignition module or coil are not ruled out, but 9/10 times those are usually RPM based problems.. ( shit the bed when you hit 3k or cut out, backfire and start running again. ) Fuel pressure or clogged fuel system would generally seem like it was running out of gas. ( lose power, sputter and so on. ) I had an 80 with a 305. I also bypassed the ignition module and had a MSD 6 in it. ( I think i probably still have the MSD somewhere ) I ran a few vehicles with it.
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It can also be the pickup coil..OP, put a mighty vac on the distributor advance can and with it idling add/remove vac....if it stumbles or dies most likely a pickup coil wire is broken...you can also pull the cap, unplug the wire connector off the module and test with an ohm meter while wiggling the wires....most likely cheaper to just go pick up a rebuilt distributor from Napa and swap...... Cannot agree with you more. The old wires to the pickup module tend to crack from the inside out with age. Better off with a reman distributor and they are not too hard to change. |
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Just replace the whole distributor. It's cheap and has a new pick up coil. I am betting on the ignition control module. If going with just that part only get a real GM one. Some have thermal paste to transfer heat, the new ones come with die electric grease which is not the same thing. I was into fieros as you can see my avatar and I had one cook off myself. Always carried a spare and tools to swap. This I had the same problem in an old blazer. I replaced the ignition module but it was the pick up coil in the distributer that was failing. |