71C10 just stops running

[71C10daily]

Hello all, Has anyone else had this problem ? I have a 71 c10 with a 350 zz4 crate motor with HEI distributor. It would not start one morning , found it had no spark - I replaced the coil, distributor cap, rotor, ignition module, wiring harness from coil to module, plugs and wires. Now it will run for about 5 minutes and just stop , sometimes it will start right up sometimes it takes numerous trys but will just stop again as if you turned the engine off. I am stumped and hoping someone else has had this problem . what do I check or replace next?

[71C10daily]

I read somewhere it could be the key ignition switch inside the cab , so I ran a wire from battery to primary coil , started the truck, it ran for about 3 minutes and still just abruptly stopped running.

[1970 CST Short Wide]

Are there any fusible links in the system. If so maybe there getting hot. Just my guess. I’m terrible are electric stuff, Sorry

[Sheepdip]

Do you have a full 12 volts to the HEI? If you used the old resistor wire to the original distributor it will do that.

I would also check your fuse panel at the firewall next time it dies to see if you have power going to it from your ignition but nothing out the other side.

[Accelo]

Run a wire with a low watt bulb from the HEI power, at the distributor, to inside the cab. See if it goes out when the engine quits.

[HO455]

Do you have a multimeter? If not it's probably a good time to get one and become familiar with how to use it. The interweb is is your friend if you are unfamiliar with multimeters.

Start the troubleshooting by checking the voltage supply to the coil both engine off and with the engine running. If you have a helper checking the voltage while cranking the engine may be helpful. You are looking for at least 12 volts in all conditions.

If your voltage is good proceed to following tests.

Check for spark when cranking, running and immediately after the engine dies. Best to use a spark plug tester or a non-LED test light to perform the test. You should not see any differences in the spark between each test. The interweb can supply you with how to perform this test. (I personally like the videos posted by ScannerDanner. Although he focuses on later model vehicles with modern test equipment he also shows troubleshooting with more basic tools. His information is good and well presented.)

The purpose of these two sets of tests is to determine if you have an ignition problem or a fuel supply problem.
Once you are sure you have an ignition issue I would try swapping a different distributor in. That will check if you have a bad pick-up coil in the distributor or some other problem inside the distributor (like a bad ground wire).

There are also videos out there that show how to check the pick-up coil. Bench testing coils can be difficult since they can operate correctly when cold but, fail or operate erratically when hot.

Low voltage to a coil during operation will cause a coil to overheat and eventually fail.
A low voltage condition while running will damage any electrical component.
Also be aware that one of the new parts may be bad. That's just an unfortunate fact of the modern world.

Just to be clear there are 2 coils in a HEI ignition system. The primary spark coil in the distributor cap and the pick-up coil under the vacuum advance plate inside the distributor.

Welcome aboard and good luck. Please keep us updated on your progress .

[71C10daily]

I did run a wire from battery to top coil (primary) ran truck and it stopped again after less than 3 minutes. Thank You for all the info/suggeestion , I have alot of checking to try. Thanks again , when I find the Gremlin ill post what I found and what the fix was.

[71C10daily]

1st problem with engine not starting at all was the ignition module . 2nd problem, After that engine starting and only running a 3-5 minutes was fixed with new mechanical fuel pump and new filter. Thanks again for all the suggestions

[71C10daily]

Thank you all for the suggestions , I'll try a few different things this weekend.

[Palf70Step]

Glad you got it worked out.