This one has got my mind doing loops.

1988 f150 custom, 4x4, 300 4.9L i6, 1 tank (two fuel pumps[low in tank, high inline])

Backstory (and I believe the source of the problem): I had my truck shipped from MO to AK (I'm in the military). The shipping company called to tell me I needed to pick up gas because they had ran it dry"warming it up for me". Showed up, put gas in. Started, but rough idle (from ~1100-400-1200,500rpm.. Yadda yadda) till she died. Sweet, I'm thinking they shot the fuel pump. Filed a claim. They denied it because it was mechanical. Damn them to hell, submit a poor Google review, move on.

The problem: After sitting for a long period of time, the truck starts right up, and idles fine and runs normally. After getting warm, it will start and run fine, idle erratically at random until it dies. Then it won't start like its starved for fuel. But I've hooked up a fuel pressure gauge, and fuel pressure stays ~45psi even when idling erratically and died.

Being stubborn and still believing that it was the fuel pump (maybe good pressure but not volume [and its old]), I replaced it. Still same issue. (Yes I checked fuel filter and lines... Fuel before and after fuel filter and in pressure relief on fuel rail). I even (just for giggles) turned ignition on with engine side of fuel line of filter disco'd... Shot fuel straight out).

Checked fuel pressure regulator (took off vacuum line), fuel pressure spiked ~10psi, as it should have.

Checked EGR. Held a vacuum just fine and killed the engine while doing so. No excessive carbon buildup when removed.

I have spark.

ICM was replaced about 6 mos ago when I had an issue of it crapping out when it got too hot.

Low pressure pump in tank was replaced about a month ago. (And would assume all is well with correct fuel pressure)

IAC valve is about 6 mos old (the old one was fine, just a broken/sheered off flange).

Distributor cap and spark plugs and wires are within the year.

No vacuum leaks from what I can tell. PCV rattles and works as it should.

Inertia switch has been reset and tested, all seems to be fine there.

Pump relay wouldn't be bad because PSI is staying where it should even as issue arises. I have a new relay, but can't get the damned old one off there. Seems pretty fused onto the harness lol.

An an interesting thing to note is that when I shoot propane through the throttle body when erratic idling, the problem goes away. Remove propane, back to erratic idling. Definitely seems to be fuel related.

I'm at a loss... Anyone ever experienced anything similar?

Im thinking of checking next:
-MAP sensor
-IAC Valve(make sure it's not gummed up)
-Pull fuel rail and check out injectors

Any advice or insight is greatly appreciated. Thanks in advance.

Mac

 

Referring to your 4th paragraph which starts The problem: When it quits and won't restart have your tried starting it on propane?

These trucks are known for ignition problems where they will quit and not restart until cool. But, unlike yours, they usually just up and die with no rough running. The most common thing to cause it to die and not restart until later is the PIP inside the distributor. Followed by the ignition coil and sometimes the ICM which I see you replaced, usually when the ICM goes dead it will never restart until the ICM is replaced.

 

Yes, I did restart it with propane after it had Idled erratically and died without propane. After it died, it wouldn't turn over (it would crank but would sputter some fuel to a no start), until I shot the propane through the intake, then it started right up.

As for the PIP, I'll have to take a look.

I'm having a hard time believing it could be anything other than something that would typically mess up with having been run bone dry on fuel (fuel pump, line, filter, injectors, et cetera). This truck drove thousands of miles without issue before this event. But then again, could have just been one of those perfect timing kind of things steering me in the wrong direction.

 

I would have to suspect crappy fuel as a possibility.
You have fuel pressure, you have spark and the truck will run on an alternate fuel source.

Possibly the injectors are plugged up or otherwise malfunctioning - could even be that they're not getting a signal from the ECM, but -

Real big coincidence that it gets run dry of fuel, you go put some in and it won't run. Coincidences happen but the fuel has to be suspected.

 

The tank got filled with proper gasoline from a big name gas station up here. I also through in a bottle of heat to limit the possibility of a large amount of condensation building up.

Ill have to see what I can do to check the ECM, but I wonder why that would cause it to have this problem of running fine for a decent period of time, and then running into the erratic idle/no start issue.

Maybe ill try running some seafoam through it before going too crazy on the injectors.

 

In the way-out-there line of thought - could the IAC be sticking or seizing intermittently? When it's idling erratically, can you throttle up a bit to get it running smoothly again?