Hi. I have a 91 f150 with a 5.0 and a m5r2 stick shift and 4x4. im having issues with it because it will be running beautiful and then all of a sudden it dies. I have checked the entire ignition system and air filter so im guessing its fuel. I also think that because its getting way worce fuel mileage than normal. What could it be.

 

Pull your codes, see the sticky at top of forum on how to do it yourself with a paperclip or short piece of wire, parts stores usually can't/won't read OBD1

"Borrow" a fuel pressure gauge from oriellys or other auto store, check initial pump pressure, pressure while running, then how far it drops after 2-5 minutes.

Does it do this with both tanks (if so equipped)?

Is there an average length of time or conditions that it does it?

Could be faulty ground, clogged fuel filter, o2 sensor issues, failing PIP sensor in distributor, failing ignition coil. The last two can check out fine, and work 90% of the time but tend to "cut out" when hot.

Please post your codes or if you are having trouble deciphering them record the CEL blinks and post a video.

Be sure to run both KOEO and KOER tests, also warm the truck up before starting the tests. Follow the directions HERE for properly doing the KOER test, if you don't follow directions you will get multiple bogus codes.

 

If you're not throwing codes, I'm wondering if you have a plugged up/rusty fuel filter?

 

Methyl hydrate in the fuel tank too, in case you've got any water in your gas. Cheapest way to buy it is by the quart in the paint section. A couple ounces in a full tank.

 

Ive found a leaking return line could that do it.

 

Fixed the leaking line and still having issues. But I noticed that when it shuts down the coil is hot as hell. Could the coil be heating up and shorting or something along those lines?

 

Yeah, a common sign of a failing coil is it "randomly" shutting off after it warms up, PIP will do the same thing.

 

You should also check your idle control valve. It could be that simple.

 

What is PIP and also I should have been more descriptive. It dies randomly whether idling or driving down the road also I noticed that it wont turn over after it dies unless I beat on the starter solenoid and battery cables. Ive replaced the solenoid already.

 

Pickup Sensor in the distributor. Both will cause random stalls and won't restart for a few minutes until they cool down.