I have a 1977 Ford F100 with a 351 windsor. I replaced the alternator in it after it went bad with a heavier duty one that I think they used in the F250s. What is happening is I will be driving on the highway for about 10 minutes and then the engine will shut off as if I turned off the key. After about 5 minutes it will start back up again. I thought the problem was in the electrical switch so I strait wired the power from the battery through a rocker switch under the dash and back to the MSD ignition. Well after driving it to work the next day the engine died again. After it sat for about 5 minutes it started back up again. The rocker switch that I have under the dash also lights up so I know if the ignition is losing power when the light goes out. Well the light never went out when the engine died so I figured that maybe the ignition is just over heating and shuts down to cool off. I did an experiment to determine if the brain box was bad by getting a brand new MSD 6A Ignition out of the box from another project that is still getting rebuilt. I installed it onto my truck and after a day or so it started again shuting down just as with the one that was in it before. So I concluded that the brainbox was not the problem. The alternator that I put in it is much bigger,looks different,has the hook ups on the side rather than the back, and puts out 70 amps. All I can say is that none of this started until after I replaced the alternator. Do you think the problem could be the alternator?
Anybody who can help with this delima will be greatly appreciated as I am having to drive my 66 mustang to work at USG (we make sheetrock) and the environment there is not very vehicle friendly.
Thanks in advance,
Matt,
Jacksonville, FL
P.S. I have pictures of my truck posted in my gallary if you want to see it.
let me know what you think.

 

check the instructions for the m s d box. i think some of them require a lower voltage for running. may be getting to much voltage and overheating the box. i am sure it has a built in protection device of some sort.



jim

 

I read the directions to the MSD ignition and found that it can handle up to 16 volts continuosly and up to 23 volts momentarily (Like when you have to jump start your car). I also performed a test on the alternator per the directions that came with it and all is within spec. I don't know what else it could be.

Matt
Jacksonville, FL

P.S. Did you look in my gallary?

 

I'm not sure about your problem, but I did look at your gallery.... You did bring that truck back from the dead huh?

I can appreciate how much work it is, since I just threw a fresh 302 in my 1980 F-150 4x4. It looks like you went the same route as I did with cast iron exhaust manifolds. I painted mine with POR-15 Black Velvet. What did you use? You also have the valve pan covers that I wanted, but someone on ebay wanted more than me... I settled for a set of vintage finned cast aluminum ones. I got a great price on them since they were painted with a brush, and needed stripped..

Anyway, I would try to find a alternator just like the one you had before....

 

I had no choice but to go with manifolds because I didn't want to notch my frame on the passenger side and also it was to expensive for me to have headers made for it. The engine use to be in another F100 that I had before which was scrapped and it had long tube headers on it then which were damaged in the accident. When I put the engine in this truck I had to use manifolds because I could not find a set that would fit and I didn't know the brand that was in the other truck. I noticed a loss in power to when I switched to manifolds. As for the paint on the manifolds, I used 1200 high temp header/manifold paint.

 

Silly question....did you confirm it's not your ignition switch, loose or shorting?

 

He hot wired the ignition to bypass the original switch.

I would get a voltmeter and check the battery voltage with the truck off. Then check the battery voltage with the truck running. This may point us in the right direction as to what the alternator is really doing.

 

If it was the battery it would go dead, So I don't think thats it. The alternator is a easy check. Get a volt meter and see what the voltage is when Idleing most run around 12.5 then run it at 2000 RPM it should read 13.8~14.2 Volts.

Sounds like the coil is getting hot and shutting down till it cools off. If it is next time it does it, Pull a plug wire and see if there is spark.

 

Are you sure it is getting fuel when it quits ?

 

To :Mark A.
I have a fuel pressure guage installed in the fuel line just before it gets to the carburetor and the guage was reading 6 psi after the engine died. It runs fine and then just like that the engine dies like the key is turned off.
To :MuffinMan and Franklin 2
I checked the voltage from the battery posts with the engine at 2000 RPM just as the directions said and the voltage was 13.8 volts steady. I didn't check it with the engine idling or when it was off. I'll do that next.
Thanks for all of yal's help. It means alot.

 

What about the ignition module in the dist ?

 

I know how fustrating electrical problems can be.

 

It could be a ignition module. I have seen where they get hot and shut down. Most the ones I seen will melt when they get to much voltage from high RPMs.

Pull the Dist cap and check the ohms and volts. I don't know what the spec's are on that model ford for it.

 

I have been thinking about just buying a new wiring harness and just replace the one in there now.