77 351M Coil Issue
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5th Wheeling
Joined: Feb 2024
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77 351M Coil Issue
I have a 77 F350 with a 351M that is having what I believe to be a coil issue. I changed the coil, distributor cap and rotor because the engine was dying and now the engine wont start. The coil is receiving about 6 volts but is outputting 0. I tried putting the old coil back in it and it still won't start. This is very bizarre because I drove the truck into the garage to work on it. I tested the coil output and a spark plug wire. Nothing. I did notice that the coil became very warm, hot even, during the cranking and testing process. I tried a remote starter to check the coil, and thinking that might be a problem disconnected the remote starter and went to the key. Still no spark. I'm pretty lost here as this is my first attempt at doing any electrical work. Any advice on other things to test or check would be appreciated.
Lead Driver
Joined: Jul 2017
Posts: 9,601
Likes: 1,174
From: San Jose, CA
What caused you to replace the coil in the first place?
And when you replaced the cap, did you put the plug wires on and exactly the same place?
Did you mess with anything else, or going into any other areas at the same time?
And when you replaced the cap, did you put the plug wires on and exactly the same place?
Did you mess with anything else, or going into any other areas at the same time?
Laughing Gas
Joined: Aug 2016
Posts: 848
Likes: 464
From: Albuquerque and Colorado
I had similar issues. Truck would just die. Then after messing with the wiring it would run fine again. I can almost guarantee you all the wiring for the Ford ignition system has corrosion.
Unless you just want to keep it stock get one of these. https://www.summitracing.com/parts/s...-150/year/1977
All you need is a key on hot source. Starts and runs great. It’s been running great for 5 years on mine.
Unless you just want to keep it stock get one of these. https://www.summitracing.com/parts/s...-150/year/1977
All you need is a key on hot source. Starts and runs great. It’s been running great for 5 years on mine.
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5th Wheeling
Joined: Feb 2024
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I replaced the coil because it was suggested that since the engine was dying after starting and running fine until reaching operating temp, that the warmth could be causing problems with the coil. The coil I replaced was the original coil. I also replaced the rotor cap, and rotor and replaced each plug wire onto the rotor cap according to the timing diagram in the Haynes manual I am using. I did some other work at the same time but nothing in the way of electrical.
A different thread for a different engine suggested that maybe the ignition module (which i think is in the distributor?) could be bad. If thats the case, how do you replace that? Do you have to replace the entire distributor? I am the first to admit not being very good at troubleshooting so I don't mind replacing parts, however i dont want to spend the next week replacing an entire ignition system if its something simple I am missing
A different thread for a different engine suggested that maybe the ignition module (which i think is in the distributor?) could be bad. If thats the case, how do you replace that? Do you have to replace the entire distributor? I am the first to admit not being very good at troubleshooting so I don't mind replacing parts, however i dont want to spend the next week replacing an entire ignition system if its something simple I am missing
Laughing Gas
Joined: Aug 2016
Posts: 848
Likes: 464
From: Albuquerque and Colorado
The ignition module is located on the drivers side fender. Wait until you see the connectors, at least on my California truck most were broken and completely corroded. You don’t have to remove any of it if you go with the new distributor. When I eventually had other electrical issues I removed all that junk a cleaned it up.
Lead Driver
Joined: Oct 2018
Posts: 7,877
Likes: 2,366
I would try a new ECM first and if that doesn't fix it try a new pick-up coil.
you're better off with the duraspark than a Chinese distributor. just fix it .
you're better off with the duraspark than a Chinese distributor. just fix it .
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Laughing Gas
Joined: Aug 2016
Posts: 848
Likes: 464
From: Albuquerque and Colorado
To each his own, im just relating my own experience. “Chinese” has worked great for me in this case.
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5th Wheeling
Joined: Feb 2024
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Another post mentioned that the firing "signal" comes from the mechanism within the distributor and to the negative terminal on the coil and that the issue may lie within that mechanism. The Haynes manual however says that the mechanism is pretty much maintenance free and there are no replaceable parts in it. What is your take on that? Could something inside the distributors solid state system be causing the coil not to send the voltage?
Lead Driver
Joined: Oct 2018
Posts: 7,877
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Might want to check that out, the made in China stickers on many MSD parts would beg to differ.
MSD gears and such are mostly US made and some of the best you can buy. their electronics are average at best in my experience. but if you go buy parts for a duraspark system they'll be imported as well, that's why you have to find NOS. get what you need to get you running then find quality replacement parts.
The only problem duraspark has that's worse than any other system is the ECM. which is cheap and easy to fix. everything else is as good if not better than any system you can buy .
MSD gears and such are mostly US made and some of the best you can buy. their electronics are average at best in my experience. but if you go buy parts for a duraspark system they'll be imported as well, that's why you have to find NOS. get what you need to get you running then find quality replacement parts.
The only problem duraspark has that's worse than any other system is the ECM. which is cheap and easy to fix. everything else is as good if not better than any system you can buy .
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5th Wheeling
Joined: Feb 2024
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ECM=Engine Control Module? Would a truck this old have that? If so where would it be located?
Pick-up coil is a term im not familiar with? Is that something different than the high voltage coil attached to the distributor?
Pick-up coil is a term im not familiar with? Is that something different than the high voltage coil attached to the distributor?
