My 91 F250 was running like a champ and it suddenly died under acceleration. No sputter, the engine just died. All gauges and radio went dead. It will not tun over and nothing works when ignition turned on. It was like someone had turned the key to off while driving. The lights work, the horn works so the battery has power and I did take the alternator in to the parts store today and it tested fine.

Could it be the ignition switch? It seems odd that it would go after 45 minutes of driving and while driving. Any help would be appreciated.

Mark

 

If you lost all power to the cab then it sounds like the ignition switch to me, if it was just the engine then I would have said ignition module but that's not the case.

 

doees your radio work? if so its prolly not your ignition switch. if thats the case thats a little confusing, if you didnt have power at all i would go for the fused link, or ig switch, but if you have power to the cab i guess it could be a loose wire somewhere. or if its real serious i suppose you could have broke something internaly(although you did bot say the engine locked up, so nevermind that)????????????/ im kinda confused

 

I think it might be the ignition switch so I will try replacing that. The radio does not work, as I said it was like someone turned the key off while driving.
Mark

 

ive seen the ignition switch pop apart before, id start there

 

I replaced the ignition switch and it did not fix the problem. Turning the key does nothing. Again the horn, flashers and interior/exterior lights work (the same as they do when the ignition is off) but that is it. I arced the starter relay to see what would happen and the starter engaged. Any other thoughts??? Could it be the relay?
Mark

 

Well, id say it could be the relay. The ignition switch runs to the relay and then you get power. A new one is only a few bucks I believe. You did say it started up when you arced the relay? Did you get power inside when it was running?

 

The engine did not start but just turned over when I arced the relay. I have had relays go before but usually I get power but the engine won't turn over, it would be odd to have the relay go while driving too but I agree it is a cheap part to replace to rule it out as a problem.
Mark

 

Forget the starting idea, I lied. Im used to working on diesels, lack of ignition. But, either way, I suppose if it turned over when you arced it and it doesnt with a key id rule out the relay first. That may be the problem. I see what youve already done.

 

Sounds like fuse link "P" is open.
The Starter relay will not cause your problem.

Diagram:
http://i54.photobucket.com/albums/g9...ams/012-02.jpg

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I already replaced the relay for a small price so it was worth it. What is fuse link "P" and how do I fix it?

 

Fuse link "P" is in the diagram I posted a link to above. One end of fuse link "P" is bolted to the starter relay battery side and very close to the relay. Try stretching the fuse links there and if it stretches it is bad.
To replace just get a some 20 GA fuse link wire from an auto parts store, cut out the bad fuse link and splice in the new.
Fuse link "P" powers your Ignition switch.

 

My apologies, didn't see the link. I'll check it out tonight.
Mark

 

The fused links appear to be in good shape. They are solid when tugged and visually appear to be fine. Still scratching my head on this one.
Mark

 

Maybe the ECU went. Mine didnt go naturally but the ignition module on it was fried and it wouldnt work... Just a thought. Youve gone through fuses, links, ignition switch. I dont know.. Just tossing ideas. Someone who knows more than me could probably elaborate on finding it out.