I have a 94 F-250, i have put a new coil, new ICM, fuel filter, fuel pump relay, gas pressure regulator. With all this new stuff put on, the truck will fire and run for about thirty seconds then it will shut off and will not fire again for quite some time. Sometimes its five minutes and sometimes it is closer to fifteen. All of the fuses are good, and it is not throwing any codes when I hook up my scanner tool. Truck has 150k on the 5.8L. Getting the alternator tested tomorrow thinking that could be possibly the last thing that i could check. I have done a tune up on the truck, put a new battery, air filter and a new ground strap that goes to the starter, I have checked the ground strap and that is intact as well. Please Help, its driving me INSANE!!

 

Can you tell us if you know if you have spark when the engine will not fire up?
Do you hear the fuel pump in the tank run for the usual 2-3 seconds when you turn the key on? The reason I ask that is there is an EEC relay that supplies power to the fuel pump relay and the vehicle computer. The EEC and Fuel pump relay are the same type and are inter changeable..
One of the things that might need to be checked out would be the pick up coil inside the distributor.. If it is opening up when heated , engine will not fire up.The pick up coil is easily verified working if you use a test light.
The ign module and computer need that RPM signal that comes from the pick up coil in the dist. If all the parts you replaced are good, and you still have no spark, That pick up coil is suspect. The dist has to be removed to replace it . There is a procedure to follow before attempting to do it, if necessary.
Forget about a scanner helping out here. OBD l does not provide the info that OBD ll does and your vehicle has OBD l.(On Board Diagnostics)
Do you have at least a test light or multimeter to work with?

As you know , you should have power coming to one of the terminals on the coil when the key is on.Check it when cold and again when it won't start
I gave you some info to check, lets see where we stand before going any further.

 

Yes it does have good spark when the truck does not start back up. I have a multimeter but I am not 100% on how to use it. I bought one because a friend of mine needed one and I was at the parts store when he called so I grabbed one and figured it was a good thing to have.

 

It should have come with instructions for it's use. You will find it was a good investment for troubleshooting a lot electrical problems on your vehicle.

The engine requires fuel, air , compression and spark at the right time to run.
There is a fuel pump driver module that can be troublesome and the better thing to consider at this time is renting a fuel pressure gauge from an auto supply store to observe if the engine is getting fuel when it will not start. We know it is getting spark, has compression and air because it will run at times. The only thing we have left to verify is fuel supply at the correct pressure.. That is why you need the pressure gauge to confirm the supply.
I don't like to suggest starting fluid because most folks use too much and that can do damage to pistons inside the engine. Suggest carb and choke cleaner since that is the closest to gasoline. If a shot of that is sprayed into the air filter at the time the engine will not start and the engine starts for 2-3 seconds,that confirms a fuel supply problem..

It is located under the spare tire mounting and if you see a lot of corrosion between the module body and frame mounting , it could be the source of the starting problem.

 

All the things you replaced but I do not see any mention of you checking fuel pressure.Do it at start up and leave the gauge on and see what it is when the engine stops. Specs are 45-60 with the 4.9 and 30-45 psi with a V8.Save your time with the alternator, that's not your problem..

 

When the truck ran it was at 70psi. Sorry I forgot to mention that at first. While it was off it was over or close to 40psi.

 

Maybe I'm a little slow this AM, but You did not tell us what the pressure is at the time it will not start, or did you?

 

It was 25 psi on the front and 42psi on the rear tank. When I tested the coil is was getting orange spark instead of the nice crisp blue spark. But it comes and goes intermittently so I was told possibly the coil that is under the distributor. It’s getting towed in tomorrow and I will let everyone know what happens.