here's the story, i have a 95 ford 250 scab 4x4 7.5 that i bought used about a year ago. I believe it was a theft recoveryor a repo, anyway the ignition switch on the column is very loose and i dont have the normal ford key(the black plastic one). (this could be part of my probelm).
The truck has been fine until this last week when the rear brake line popped which dumped fluid from one end to the other. once that was repaired things were good unitl yesterday, stopped for gas and when i restarted it run for only a few seconds and shut off. then it would crank over. I put a scan tool one it and it said system ok, no spark though and the fuel pumps are running up to pressure. I installed a new cap, rotor, coil pack, ignition module and still nothing. I shook a few connectors here and there and the truck started. once i had it home, i changed the power distribution solenoid by the battery and the truck failed again. no power to the coil. with the key on after many retries to start i unplugged the fuel pumps and plugged them back in and the truck started and has been running since. Do the fuel pumps have something to do with power the coil? I need the truck but can not depend on it at the moment. thanks for any input

 

Could be the computer is going bad. I had one on my '88 go bad. Just like you state, everything works, just no spark.

Mike B

 

NO, the FUEL PUMPS have nothing to do with the power to the coil and the COMPUTER (PCM) has nothing to do with the power either.

The path for the power to the coil is:

Batt+ post to Starter Relay on finder.

Relay Terminal to FUSE Link A & B.

From A & B over 37 Yellow wire to Engine Compartment Fuse Box, FUSE P 50AMP

From Fuse P over 37 Yellow wire through connector C202 & Splice S234 to Ignition Switch C269 & B5.

From B5 out I1 through C269 over a Red/Light Green (16) wire through S206 & C202 to Engine Compartment Fuse Box Fuse U 20 Amp.

From Fuse U over R/LG (16) through S148, C101, S199 and C1008 at Ignition Coil.

COMPUTER (PCM) are either good or bad, they are never in the mode of going bad. They are made up of solid state components with a life expectancy of about one million years. They fail in a instance when they let the smoke out.

 

To help you follow my description:

 

that's the magic smoke of electricity

 

I would actually disagree with that. PCMs aren't like light bulbs where they are either working or not working. PCMs (all computer parts, to a degree) can sort of work. Sometimes they'll work better than others, sometimes they'll be worse. A lot of it has to do with temperature and humidity. If there is an iffy connection on the logic board, it can open and close just because of the temperature of the components. There's an in-between state where electrons can sort of flow through the partially closed circuit but at a higher resistance. This can lead to unpredictable behavior at the very least.

Given the original poster's description, I would start looking for bad grounds first. Bad grounds can lead to all sorts of electrical problems, some of which you wouldn't ever guess.

 

Then the possible source could be a bad ground or maybe the Ignition switch assembly on the column?
the biggest reason for my concern is safety, I would not want to be on the highway when it cuts out.

 

I was going by your first post and if you were losing power at the Ignition Coil, then I would say the Ignition Switch is a good bet. Were you using a test light when you said you had no power?

 

yes, at the positive side of the coil. when it would only crank over.

 

Title edit - https://www.ford-trucks.com/forums/s...d.php?t=399714

 

well so far it is still running, not sure what change to keep it going. I installed a new ignition switch last night just so i could rule that out as a possiblity if it happens again. I think the only thing left would be the grounds. Does anyone have the diagram that tells you where they all are?

 

There are no grounds that would keep power from getting to the Ignition Coil.
However make sure that the two grounds coming from the NEG side of BATT are good G103 (ENGINE) and G101 (BODY) as if you lose the ground going to the PCM the engine will quit.

Also make sure both BATT Terminals are clean.

 

well it is down again, my daughter broke down in the middle lane of the highway. it just shut off. we had it towed home. same problem. new solenoid at the fender same, no power to the coil or at the solenoid.(old and new). turns over with no problem until the battery is dead.

 

any input on the obd1 scan tool, I have check the truck using the tool and it says the system is ok. would such a tool check fuel pumps, fuel regulator, and ingintion stuff?

 

Quote:

Originally Posted by kenjan61

well it is down again, my daughter broke down in the middle lane of the highway. it just shut off. we had it towed home. same problem. new solenoid at the fender same, no power to the coil or at the solenoid.(old and new). turns over with no problem until the battery is dead.

The solenoid is just a tie point, the power to the coil does not go through it.

How are you checking for power, test light, meter?

Check to see if you have power at Fuse "U" with the key on. It is in the Engine Compartment Fuse Box, the fuse is in a square box under the hood on drivers side. Check both sides of the fuse.

If nothing there check fuse "P" in the same box.