1995 F-150 XL, 300/M5OD 2WD

Since about 2 months after I replaced my front fuel pump, I've been having some fuel problems (could be coincidence, could be the pump?) Here's the symptoms:

Truck runs great. Very smooth idle, no funny noises, breeze to drive, good power, etc. Until every once in a while it will just lose fuel. I'll either feel it buck on the road, or I'll try to start it and get nothing. Sometimes the check engine light turns on while it's happening, and other times it doesn't. I bought a digital code reader and the only codes I've ever pulled are air ones (MAP, TPS, etc), but I'm sure that's because it wasn't getting fuel at the time, and the CEL goes away once it starts running again.

When it really acts up, the truck simply will not start. I exclusively use the front tank (the one i replaced), but the rear pump works as well. When the truck won't start, changing to the rear pump doesn't change anything. The weird thing is, I can hear each pump prime when it won't start and i flick the switch, as they should. This leads me to believe the pumps are getting pumping fuel past the tanks.

I know it's fuel because if I spray a little bit of starting fluid in the throttle body, she acts like she wants to run.

I thought that it might be my ECM not firing the injectors, so I replaced that. No luck.

The weirdest part is, as soon as the truck decides to play nice, it runs like a champ like it always did.

I'm pulling out my hair here, and really want to be able to drive my truck to and from work without worrying about getting stranded.

Anyone have any ideas? I'm thinking about warrantying the pump to be safe, but that doesn't explain why the rear one doesn't work when she's acting up. I thought there might be a physical blockage in the system, so I pulled and cut open the fuel filter (only has about 6-8k miles on it anyway) and it didn't look bad at all.

Here's a list off the top of my head of new parts within 10k miles:

Fuel pump, front
Fuel filter
ECM Computer
Spark plugs
Wires
Dist Cap/Rotor


Anyone have any thoughts? This only happens probably once or twice a fill-up, but I work about 20 miles away and can't risk being stranded. I want to drive my pickup! Help!

 

You have to prove to yourself that it is in fact a lack of fuel...could be, and probably is an electrical problem. Install a fuel gauge to confirm your hunch.

 

The last time it didn't start, I sprayed starting fluid in the throttle body and it starting sputtering, acting like it wanted to fire.

It fired eventually, but the starting fluid didn't necessarily help it start.


Anyone know if there are any sensors that control fuel rate? ICM is spark only, right?

 

You really should use a pressure gauge to check that out so it is eliminated...have you checked the fuel regulator for signs of fuel in its vacuum hose.

 

it's dry. I'll check the pressure, but I have a feeling it will be in spec...while it's running. Are there any cheap fuel pressure gauges online, so I can keep one in the dash?

 

quote
I'll check the pressure, but I have a feeling it will be in spec


you want to see what it is during the no start, you said its running out of fuel...I would check for spark at that time aswell


I would say to forget the dash. Buy a gauge and keep it in the truck with your other test equipment, for any future episode on the side of the road...or, you may be able to borrow one from Auto Zone

 

I would want to check output pressure & flow rate up at the engine (yes, when the truck has failed to start from an apparent lack of fuel delivery).

 

I had my 89 did somthing close to his problem. Had good fuel pressure and spark but the ECU would not fire the injectors. It would run on starting juice. I finaly found a bad PIP connection going to the ECU.

Without the PIP signal(from the TFI modual) the ECU will not fire off injectors. Also my truck did not did not have any codes so it was a hair pulling ordeal till it hard-faulted a few blocks away from home. And I was able to track it down.

 

I think I may have stumbled onto my problem. I was researching and found this picture yesterday, listing common shorts in our pickups:



From my problem described, I looked at number 8, the canister purge solenoid. It makes sense to me that the problem may be vapor lock (fuel pumps both stop pumping fuel when there is air in the lines, has happened after sitting for not long and then restarting, bleeds itself out eventually, etc.

The wires looked good but I pulled the purge valve solenoid and it looked completely closed, which I'm not sure if it should be when the circuit is 'open'. Also, I can rotate the connector end of the solenoid and the pins rotate, which probably shouldn't happen.

I took a vacuum connector and pulled and bypassed the valve, and took her for a drive. I feel like I've gained a little more smoothness in the powerband, and she hasn't hiccuped on me yet, though the drive was only about 15 miles.

I'll keep everyone posted, but if it won't start again, I'll try to get a gauge on it.

 

Nice find!

I added it to the tech sticky, too.

 

Well, I finally got a fuel pressure gauge on it the other day and found out fuel pressure was great. The truck decided not to start anymore so I could actually diagnose the problem.

Module tested good, I replaced the coil because it was cheap but to no avail. Ended up being the pickup coil in the distributor, which I replaced the whole unit. Not too bad of a job and now she's purring again!

Thanks to everyone who helped.