I've got a 72 F250 with a rebuilt 390. The problem I've been having for about 4 years is the engine will shut down. I had this problem before the engine was rebuilt and still have it. It happens in hot weather, cold weather, engine warmed up or engine cold, going uphill or downhill, making left turns or right turn
or going straight. There is absolutely no consistancy. It just quits when it feels like it. I pull to the side of the road and it will usually start right up. But sometimes it won't fire at all, and I'll give it a few minutes and it will start up and off I go. It might travel 50 feet before quitting again or as far as 1300 miles. I've more or less eliminated any kind of fuel supply problem. I have changed the coil, distributor (whole thing), voltage regulator, coil and plug wires,solonoid, and ignition switch. It won't stay broken down long enough to trace the problem.
Someone suggested the resistor wire to the coil is bad. I checked the voltage with the engine running and it gets a steady 12 volts. Is this right?
Can anyone help me before I drive it over a cliff.

 

It should be closer to 9 volts....maybe the resistor has been bypassed by a previous owner...and then maybe the coil is heating up from the extra voltage........or maybe it is gremlins but seriously the voltage should be lower than 12 volts when the key is in "run".

ps
Dont drive it off a cliff just drop it off at my place

 

Sounds like either the coil, the condenser and/or points are bad. They are overheating and either breaking the circuit or shorting out.
This could be caused by a full 12V to the points when the key is at RUN - when it only should be 6V to 9V maximum.
There are (or should be) two small posts on the front of your starter solenoid. The one next to the battery cable comes from the key. 12V goes to this post through the ignition switch to activate the solenoid when the key is turned to START. The other small one (next to the starter cable) is active with 12V when the the key is at START and the solenoid is activated. If there is 12V at this post when the key is in the RUN postiion, then you have a bad solenoid.
The full 12V is needed when cranking the engine to get a hotter spark for starting. Otherwise, it only needs about 6V to produce adequate spark while running. The resisitor wire drops the voltage down while it is running, whereas the starting wire provides full current - but only while cranking.
If you are getting a full 12V at the coil/points with the key in the RUN position, something is cross connected or shorted out. The continuous 12V will burn your points, condensor and coil out quite rapidly.
Check your system for mis-configured wiring.

 

With the engine off and the key in the run position, you will see 12V at the coil. When you start the engine and it is running, that is when the resistor starts doing its job.

Start your truck and thump or jiggle your keys and see if it shuts off. Sounds as if the switch is loosing contact. I've seen it happen when you have an "over-loaded" keychain- the weight of all the keys wears out the switch over time.

Good luck-

Joe

 

Joe: Good call on the key chain and switch, I hadn't thought of that.
However, I have to disagree with you on the 12V to the coil at RUN.
If you look at the wiring diagrams, the resistor wire is the only wire sending juice to the coil when the ignition switch is at RUN.
It is at START that both wires, the resistor wire and the START wire from the soelnoid supply juice to the coil. Since electricity takes the easiest path (like water), the coil will get a full 12V.
Once the switch flips back to RUN, the 12V circuit is switched off, so that the coil gets only 6V.

Of course, this doesn't apply to electronic ignition systems, even the ones available as early as '65. They get a constant 12V to the system regardless.

Hope this helps.

 

I had this same problem on a Bronco a few years back, checked and replaced everything, ** except the battery cables, because they looked fine. In reality they were badly corroded inside the coating, for what ever reason it would kill the engine randomly, then it would start again, after coasting to the side of the road.
I can,t say this is your trouble for sure, but it would be worth a check. Good Luck! Those kinds of things drive you nuts, using the cliff option is only a permanent solution to a temporary problem.

 

Are you sure?
When I installed my Mallory system, the instuction said that I had to use a ballast resistor, or risk frying it.

 

"...If you look at the wiring diagrams, the resistor wire is the only wire sending juice to the coil when the ignition switch is at RUN..."

Yeah, you might be right on that one, I'm not sure. I ripped out the original resistor wire a long time ago. I'm using a ballast resistor and that's how they work- when there is no current flow, there will be 12V showing at the coil (engine off- key in run position). When the engine is running, there is current flowing at that time. This is when the resisitor starts working due to the flow of current that occurs when the engine is running. Try it and see.

Joe

 

my 85 had the same problem, it turned out to be the control module, (little silver box on the driver fender) I don't know if your truck has this, but if it does it is a very good possibility. Cost me about 30 bucks. If it stops and doesn't start, get out and give it a couple of "love taps" with the 2lb sledge. It'll work.

 

I had a 64 F-100 that gave me the same grief for about 4 years.
One time it would not start back up. I removed the fule line from the fule pump and there was a rubberband stuck in it. I thought back to when I bought the truck and it had tin foil over the gas filler hole. I removed the tank and got a sandwitch bag out of it.
You could look in the tank and see nothing but the bag was invisable in the gas. (sandwitch bag held on with a rubber band)

 

Thanks for all the tips. Since I've changed out all the parts mentioned, I'll concentrate on the resistance wire. I think I'll change it out for a regular wire and put a ballast resistor in it. Two questions-The only wire going to that post on the coil is the resistor wire. Is that correct? does it go directly from there to the switch?

Thanks for all the suggestions

 

the electronic ignitoin they are speeking of is the factory electronic available on later model trucks the mallory system uses a provided ballast resistor to limit voltage to the coil and unilite to six volts

 

Your post that you had elemated fuel pressure as a problem but the problem sounds a lot like a fuel filter, bad fuel pump or a pluged pick up tube in the fuel tank.

 

Tom41ks,

I changed the fuel filter twice and even put in a new fuel pump
(what the heck- they're cheap). The reason I don't think it's a fuel problem is that once when it broke down, the engine cranked over fast, but no firing. I poured a teaspoon of gas right down the carb and still no firing. I pulled the gas line off, cranked it over and it was feeding tons of gas.

Thanks