Intermittent 12v cutout while driving
Thread Starter
Safety Car
Joined: Mar 2000
Posts: 3,544
Likes: 448
From: Central Pennsylvania
Intermittent 12v cutout while driving
So both at idle and driving I have a 76 with a stock HEI system that simply dies. The coil, rotor and ignition module have been replaced and the problem still occurs. Sometimes the car will fire right back up and run for awhile before it happens again. Other times the car won’t restart right away but will start after it sits for awhile. Normally I’d go with a coil starting to take a crap but the problem continues after multiple coil swaps. I’m stumped. Could battery be shorting internally? Could alternator have an intermittent hick up? Ignition switch in the column? Bulkhead connection? Bad ground someplace?
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Change out the pickup coil....or stab a new distributor in it.......
70's pickup coils were notorious for intermittent contact separation......contacts open under heat......close when cool.....
Jebby
70's pickup coils were notorious for intermittent contact separation......contacts open under heat......close when cool.....
Jebby
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
This is really hard to diagnose remotely.
What all loses power? Just the HEI module? Lights and gauges, too? When you try to restart, does the engine crank but not fire, or no crank? Have you tested with a multimeter during one of these incidents?
I'd start by checking all of connections at the battery, chassis ground, and at the starter. When my car did this, it turned out to be a loose battery lug. That would only apply in your case if you were losing power everywhere.
What all loses power? Just the HEI module? Lights and gauges, too? When you try to restart, does the engine crank but not fire, or no crank? Have you tested with a multimeter during one of these incidents?
I'd start by checking all of connections at the battery, chassis ground, and at the starter. When my car did this, it turned out to be a loose battery lug. That would only apply in your case if you were losing power everywhere.
Thread Starter
Safety Car
Joined: Mar 2000
Posts: 3,544
Likes: 448
From: Central Pennsylvania
On occurrence all accessories work and the engine cranks. Test light also shows 12v into the coil on the BATT wire and maintains current when cranking. The car just won’t start. It’s getting plenty of fuel so it’s not liquid related. Battery terminals are tight. Will check connections at starter.
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
On occurrence all accessories work and the engine cranks. Test light also shows 12v into the coil on the BATT wire and maintains current when cranking. The car just won’t start. It’s getting plenty of fuel so it’s not liquid related. Battery terminals are tight. Will check connections at starter.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Tech Contributor
Joined: Jun 2004
Posts: 20,905
Likes: 962
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
On occurrence all accessories work and the engine cranks. Test light also shows 12v into the coil on the BATT wire and maintains current when cranking. The car just won’t start. It’s getting plenty of fuel so it’s not liquid related. Battery terminals are tight. Will check connections at starter.
While I think/agree that the previous suggestions/recommendations are proper and well-thought out, I suspect most of us in the audience would feel better if you got an actual reading with a voltmeter.
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From: Sunshine Coast, Queensland, Australia
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In answer to above, Snap on test light shows voltage. I use my test light often to do a quick charging system check when installing new batteries. As in, yup, 14.2 volts at idle, it's working.
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Drifting
Joined: Oct 2020
Posts: 1,567
Likes: 576
From: Wisconsin
I had a bad connection at the HEI distributor itself (on a new distributor). The terminals either came unseated or were never seated properly in the module connector. It actually got hot from the intermittent contact and melted the connector. I found it when I bumped the wires with it running and it stumbled and quit.
Drifting
Joined: Jul 1999
Posts: 1,542
Likes: 43
From: Plano TX
First thing I usually replace is the module but this hasn't fixed the issue. As others have mentioned it's probably the pickup coil. Every time you mess with the module the two wires to the pickup get moved then probably connect enough. Later on the connection fails.
Pain to replace the pickup coil as it requires pulling the distributor, removing the gear pin then slinging out the main shaft.
Pain to replace the pickup coil as it requires pulling the distributor, removing the gear pin then slinging out the main shaft.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
First thing I usually replace is the module but this hasn't fixed the issue. As others have mentioned it's probably the pickup coil. Every time you mess with the module the two wires to the pickup get moved then probably connect enough. Later on the connection fails.
Pain to replace the pickup coil as it requires pulling the distributor, removing the gear pin then slinging out the main shaft.
Pain to replace the pickup coil as it requires pulling the distributor, removing the gear pin then slinging out the main shaft.
You can also test an HEI distributor on your bench before you put it back in.....all you need is 12 volts, a plug wire and a plug.
Jebby