A fuel issue does not just shut off like turning the key off.

I did have a non-Ford that would do almost the same thing, just shut off. This was a before DSII system, Prestolite system.
I knew it was a spark issue because the tach would go to 0. Same if trying to start if the tach did not "bounce" it would not start / run.
This went on for some time till it just died.

One day I needed to move the car and would not start even after changing the box and checking wiring. I had a RTR dist and dropped it in.
I am sure it was the pick up coil in the dist. and have changed it but never put it back in the car.

That is why I said pickup coil in my other post. I think it would heat up or something like it and stop.
Dave ----

 

 

Whenever I would get the IDM error on a Taurus SHO, replacing the ignition module fixed the problem. The piece in the distributor instructs the ignition module when to fire the coil; the IDM circuit is the computer's interface to that module.

 

alright then hows your battery cables/terminals/grounds?

does it crank strong and fast?

 

This is certainly a headscratcher. Seems like a big clue, but I can't make much sense of it. Why no spark again until you turn the ignition all the way off and then back to start?

Initially I thought this may because some ignition systems use full battery voltage for starting, and then reduced voltage (via a resistor or resistor wire) when in run. If my hunch was correct, perhaps something in the ignition system was marginal and when it failed, it would only respond to full voltage, but not reduced.

I was about to pat myself on the back for cracking the mystery, but look at the ignition wiring diagram for this truck, on page 29 here:

1986 EVTM - Gary's Garagemahal (the Bullnose bible)


Look at the resistor wire between splices S401 and S216. Was that the secret? At first glance it seemed to be, but look how that resistor wire is permanently bypassed via splice S257. Whether in run or start, I can't see any scenario where that resistor wire ever does anything. Electrons are just going to take the path of least resistance, and go around the resistor wire. The coil and distributor module will both receive full voltage in run or start.

Can anybody make sense of that? If you didn't have the wire between S401 and S257, it would make sense to me, with full voltage in start, and reduced voltage in run. Is that a mistake in the wiring diagram?

 

i think it is the ignition switch too.....which was already replaced.
but in my experience the faulty ignition switch or adjustment caused cranking issues not running issues. like contorted carpal tunnel limbo dance positions while starting.

oh well i need to bug out and quit "helping"

my Willie Sutton approach hasnt been too effective lately

 

Ok don't know if the power wire is a full 12 volts or is thru a resister wire but .....
Something I would look into is "hot wire" it to by pass the IGN switch to see if it still happens.
If it does not then it has to be the switch or wiring from switch to the IGN box.
If it does happen then it has to be something from the IGN box on like the box, pick up coil, coil or wiring to all that.
Dave ----

 

Dave, I think we're both on the same general path here. My thoughts were to rig up a long test lead so you're able to check voltage the instant the engine acts up. Your plan is to rig up what should be a reliable power source and see if that keeps the problem at bay. Variants of the same theme, either should work.

The only thing I'd add: For the hotwire plan, make sure you can quickly shut off the engine in an emergency. I'd hate to see some unrelated issue suddenly crop up (loss of oil pressure, for example), and you can't turn off the engine fast enough.

 

I guess you are right about being on the same page.

As for a way to shut it off in an emergency I would say screw it as it has pissed me off this much so far let it blow or better yet burn to the ground!
But that's me.
Dave -----

 

Lol, but whose truck are you preparing to burn?

 

LOL if his truck was mine and it was giving me as much trouble it would be the truck.

I had a VW bug that when hot out and you started driving it the brakes started to lock up as you used them to the point it would not move.
It did this to me so many times it pushed me over the edge one day. It stalled and when I tried to roll it out of the road I wanted to hit a tree and wreck the car and because of the brakes it would not.
That even pushed me over more and punched out the radio got out and thru the keys at it and missed and went into the bushes and I walked a block home.
I had a buddy with me and when I get home I told dad to go get the POS. My buddy had to tell him where it was with the keys.
I never did drive that car again and was scraped a year latter.

So yes if that truck was mine and gave me that many issues I would not care if it burned up!
Dave ----

 

Did you ever get this fixed? I have the exact same issue on my 89 f150 5.0 4 speed manual

 

I never could get it figured out. I ended up tearing the truck down to the frame with the intention of building a bulletproof truck. But, I ran into roadblocks and ended up scraping it and bought a 69 f100. Good luck to you!