Engine suddenly cuts off
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Cross-Country
Joined: Oct 2023
Posts: 62
Likes: 4
From: Monument, CO
Engine suddenly cuts off
The last several weeks, my 79 F-150, 351M 4sp, has decided to just suddenly stall with no warning. There's still power, as the warning lights come on. I push the clutch in and turn the key to start and it always immediately fires up, no prolonged cranking or anything, and drives just fine again. This could happen once then again the next day, or it could go several weeks with no problems. The engine always starts fast with minimal cranking when cold, and it runs smoothly and strong. I don't think it's fuel, I changed the fuel filter yesterday just in case, and it still did it yesterday. It's almost like the ignition system cuts out for some reason. Any troubleshooting hints would be greatly appreciated. I don't have much experience at all with the Duraspark system.
Thanks in advance!
Thanks in advance!
Lead Driver
Joined: Oct 2018
Posts: 7,864
Likes: 2,359
It sounds like you're saying it just shuts off, it doesn't just slow down and die. if that's the case it certainly does sound like ignition.
I would check all the connections in the system and look for bad wires. pull the plugs apart and clean them. and then anytime you have a problem with a durashart system the ICM is suspect so replace it and put your old one in the glove box. you never go anywhere without a spare.
I would check all the connections in the system and look for bad wires. pull the plugs apart and clean them. and then anytime you have a problem with a durashart system the ICM is suspect so replace it and put your old one in the glove box. you never go anywhere without a spare.
Tuned
Joined: Sep 2024
Posts: 269
Likes: 81
yes this totally sounds like a bad power or ground wire... I'd be checking those out. With it running I'd also do the jiggle test... (wiggling potential problem wires) to see if you can cause the stall. I doubt it's fuel as well
Laughing Gas
Joined: May 2021
Posts: 1,159
Likes: 358
From: Anderson, California
Ha, I've got one of those "jiggle" wires on the Prestolite ignition on my '77 AMC Jeep 304 V-8 engine.
I had to replace the pick-up coil in the distributor and the wires are super small and delicate. I did a soldered connection too.
The ignition may go for weeks at a time between protests (sudden stalling), or months. Lately I added some extra elect tape between the wires at the connection.
I haven't had a Dura-Spark fail for several years, but usually they failed me when sitting in traffic, and won't re-start, resulting in pushing the vehicle off the street.
Intermittent problems are the tough ones to diagnose, _ _ and many times resulting in parts changing for problem isolation.
You might have a compromised crimp-fitting that is loosing continuity on occasion.
I had to replace the pick-up coil in the distributor and the wires are super small and delicate. I did a soldered connection too.
The ignition may go for weeks at a time between protests (sudden stalling), or months. Lately I added some extra elect tape between the wires at the connection.
I haven't had a Dura-Spark fail for several years, but usually they failed me when sitting in traffic, and won't re-start, resulting in pushing the vehicle off the street.
Intermittent problems are the tough ones to diagnose, _ _ and many times resulting in parts changing for problem isolation.
You might have a compromised crimp-fitting that is loosing continuity on occasion.
Thread Starter
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Cross-Country
Joined: Oct 2023
Posts: 62
Likes: 4
From: Monument, CO
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Lead Driver
Joined: Oct 2018
Posts: 7,864
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That's the distributor cap. the pickup coil is in the bottom of the distributor; it has wires going to it that plug in outside the distributor.
It's essential it be in good condition or it will cause all sorts of problems including not running at all. I've never seen one fail as you described, but it could be worth changing if nothing else works. it's not hard to change if you know the little tricks, if you decide to change it ask before you start it'll save you headaches.
It's essential it be in good condition or it will cause all sorts of problems including not running at all. I've never seen one fail as you described, but it could be worth changing if nothing else works. it's not hard to change if you know the little tricks, if you decide to change it ask before you start it'll save you headaches.
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Thread Starter
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Cross-Country
Joined: Oct 2023
Posts: 62
Likes: 4
From: Monument, CO
Were not talking about the same thing, im thinking. The coil on my engine has a cap attached on top of the coil and two thin wires that go over to the distributor body (not the cap). In addition there's the stndard high tension wire from the top of the coil to the center post on the distributor cap,
Lead Driver
Joined: Oct 2018
Posts: 7,864
Likes: 2,359
That's just a connector, the small wires going to the distributor are the ones that connect to the pickup coil.
That connector on the coil is a good place for a problem like you're having, I had to replace mine the other day because the wire was about to break.
That connector on the coil is a good place for a problem like you're having, I had to replace mine the other day because the wire was about to break.
Thread Starter
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Cross-Country
Joined: Oct 2023
Posts: 62
Likes: 4
From: Monument, CO
So to be clear, these are the wires I'm speaking of. It's a coil setup I'm not familiar with, along with the Duraspark system. The 2 wires on the coil "hat" look weak (you can see the exposed conductors) and suspicious to me. My older Clevelands used the old-fashioned coil wiring. Can I buy that setup someplace without having to buy the entire Duraspark distributer?
Lead Driver
Joined: Oct 2018
Posts: 7,864
Likes: 2,359
You can buy a new one at most any parts house. the exposed connectors are no big deal, as long as they're making a good connection and the wires aren't breaking or pulling out.
I like to solder the connections, but you could use butt connectors to splice the new one in.
It's not likely this is your problem, but it could be. the ignition switch or it's wiring might be a cause also.
I like to solder the connections, but you could use butt connectors to splice the new one in.
It's not likely this is your problem, but it could be. the ignition switch or it's wiring might be a cause also.
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