hey guys,

its been awhile, new problem, truck drives fine for a day or two, could be a week, then just stops, no sputter. let it sit for about ten minutes then it runs fine.
took it to a camp trip, and it ran fine for 167 miles, once to the camp site, it quit, let it sit, starts right up.
had a 79 ford that did this and once I changed the ignition module, the problem went away.
so I changed the ignition module on the distributor and it still has the problem.
any ideas?

Thanks

 

First confirm that you have no spark. Then check for +12 volts on the positive side of the coil primary. If 12 volts is not there, check your ignition switch and wiring. I

If 12 volts is there hook a cheap $4.00 test light between battery ground and the negative side of the coil primary. The light should glow with the key on and engine off. If it does not glow, your coil may be bad, or the wiring from the dizzy to coil may be shorted.

If the light does glow, crank the engine over with the light connected. If the light flashes, the TFI/pickup are probably OK, and the coil or rotor or distributor cap is bad.

If the light does not flash curing the crank test, the coil is not being fired by the TFI/HALL effect pickup. Check the quality of all of your ground wires -- the battery, the block, the frame, the radiator support. If this looks OK, the likely culprit is the Hall Effect pickup coil underneath the reluctor in the distributor bowl. The part only costs about $20, but changing it requires removing the distributor drive gear. This is a bit hard on Fords because it is a semi-interference fit. A press is the best way to get it off, but you can pull it with a vise, some brass drifts, a hammer, and plenty of patience. The easy way out is to get a whole distributor (rebuilt unit, or junkyard). Just make sure it has the correct (iron) drive gear. The car 5.0 dizzys had a steel gear which will eat your truck's cast-iron camshaft gear.

 

so why would the truck restart within minuts after stopping? does it need time to cool?
How about a cracked distributor cap?

 

Your exact problem happened to me. It took a long time to troubleshoot, because it would fix itself as I would try to troubleshoot it. Here is my theory:

The interface between the TFI and the Hall Effect coil is a relatively low level electrical signal. If the electrical parts have deteriorated a bit with age, the signal weakens further, and the interface becomes sensitive to ground shifts and to temperature. The TFI module just doesn't see the vanes in the reluctor passing by the pickup coil anymore, and won't fire the coil. Let it cool down a bit, and the TFI starts to recognize the marginal analog input and the truck starts right up.

Fixing the grounds seemed to help this for a while. Then the problem came back. I got sick of troubleshooting a problem that would fix itself, so I swapped out all the easy to change ignition components (TFI, distributor, coil, rotor, cap). No help.

It wasn't until I changed out the pickup coil that the problem went away for good.

A cracked distributor cap will usually cause rough running when the weather is cool and damp. It usually won't cause a "no spark at all" behavior. But that's why I suggest the test light -- isolate the problem to the low voltage or high voltage side of the ignition system.

 

yep, I changed the spark plugs ( the old ones were gapped at 35) and wires (the wires were cracked anyway) cap and rotor, thought it was gone but came back two days later, will try the "light" theory and go from there...

good camping,
scouterspokane