Ok I am beating my head against the wall, when the truck has been sitting for a couple of days, you can jump in, turn the key, the engine will start right up and you can drive as far as you want, all day if you like, the engine runs great with no signs of any problems at all, here is where the problem comes in, once you turn the engine off (engine at operating temp), it will not restart, the engine spins over but will not restart.

Also I have noticed that while the engine is still cold, the engine will restart a couple of times (after the initial start) until the engine starts coming up to temp (around 110 deg or so) and then it will no longer restart. But, and this is interesting, like I said earlier, on the first start, the engine runs great but if you shut it off (after 20 seconds of running) and restart (again, engine still cold, the engine will usually resart but will stumble and run rough for a few seconds and then level out and run good. Once the engine reaches operating temp and you shut it down it will not restart, usually for about two days.

The Fuel pump comes on and the fuel pressure is good. (all circumstances)

Even when the truck won't restart I still have spark, although it looks a little weak to me, I definately have spark.

Compression is good and within specs.

I always went on the assumption that if you have fuel, spark and compression then the engine will run, apparently not!!!

About the engine and truck, it is a 94 5.0L MAF with 189,000 miles, I have recently changed the Cap and rotor button as well as the plugs and wires, (a couple of months ago and the truck has been running great up until this). Oh I also swapped the coil from a donner truck just to eliminate that.

The truck does have straight exhaust with no cats or mufflers.

 

When it does not start does the fuel pumps run all the time the key is on?
Sounds like the fuel injectors are not firing. You may want to put a noid light on an injectors plug to see if it is getting the grounding pulse.

 

Not sure if the fuel pump is staying on, but the fuel pressure stays good.

I will pick up a Noid light and check.

Oh, and this truck only has one pump, in the tank and it was replaced about 15,000 miles back.

 

I picked up a Noid light kit last night and will test today to see if the injectors are firing, I will post the results.

The odd thing to me is that when it does start (after sitting a day or two), you can drive it all you want with no issues whatsoever, just don't turn it off because it will not restart once it is hot.

I drove it for two hours a couple of weeks ago just to see if some sort of drivability problem would surface in order to help me trouble shoot the issue, It ran great but when I got back home a switched it off, it would not restart, not for two days, and then just like a new truck it fired right off.

 

i had the same problem with my 91 F-150 5.0 i replaced my PCM (engine computer) and my truck not only restarts every time but it runs noticeably better i think these trucks have issues with water getting into the computer,

there are really only 2 things it can be your hall effect sensor in the dizzy or the PCM one way to check is to remove the SPOUT connector (the one you remove when you set ignition timing) when the truck will not start and see if it makes a difference and leave it unhooked and drive it to see if theres any difference if it goes away i would replace the distributor if not i would get a new computer, dont worry though theyre only about $125 at NAPA

 

It does not sound like a PIP sensor in the distributor (he has spark) but I was also thinking he has a bad computer. But I wanted him to use the noid light first and if it did not flash then I was going to tell him he more than likely has a bad computer if he has power at the power pins of the computer and a good ground on the ground pins.
Of course the PIP has to get all the way back to the computer to fire the injectors also.

 

I had a similar problem. Mine would fire the first time every day just fine and then if it sat for a few minutes or several hours it was usually ok. However, if it sat for more than a few minutes and up to several hours it was hard to start. Whe it did start, black smoke would blow out the tail pipes. It turned out that several injectors were leaking fuel on shut down and flooding the engine. I just replaced all 8 injectors and problem solved.

 

Yes that could be it also or a bad Fuel Pressure Regulator but first we still have to find out if the noid light flashes when the engine does not start. If the noid light flashes then yes it could be one of those two things.
I am just trying to take him in an orderly manor so he does not buy things he dose not need to fix it.
Unless I missed it he did not say anything about black smoke.

 

The black smoke was only when it first fired up and it wasn't that much. The only reason I noticed it is because I have dual exhaust and saw some of it on the driver side. If he has single exhaust or wasn't looking he may not have seen it. I agree though, don't go out and buy a set of injectors yet, it may be a waste of money.

 

Sorry it took so long to post the results, it's been a crazy weekend.

NOID light flashes even when the engine won't restart, so I would assume the injectors are firing.

Now I did notice that it does seem to be flooding, when it won't restart simply by turning the key, I can hold the accelerator pedal to the floor and it will finally restart (after 30 seconds or so of cranking) and I do get black smoke and very rough running for a minute or so just like it was loading up with fuel.

I was thinking that since it was injected, that flooding could not have been the issue, my mistake. So you are saying that the injectors may not be closing after the key is turned off and thus flooding the engine, makes sense and coincides with the symptoms I am having.

Now the big question, should I replace all of the injectors ($75 ea at NAPA) or do I pull them and take them to be tested and only replace the bad ones. I would think that if I just replace the bad ones, then the remaining ones would fail before too long anyway (189K Miles).

If anyone has any other ideas please let me know, and thanks for all of the help so far.

 

Check the Fuel Pressure Regulator.
With a cold engine short pin #6 to pin#2 of the EEC Self-Test plug and turn on the key.
Pull the vacuum hose off the FPR nipple and see if any fuel comes out of the nipple or there is any fuel in the hose. If there is the FPR is bad and more than likely your problem.
If not then go after the injectors.

The Self-Test Plug:


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