After letting my 1986 F150 302 EFI sit for a couple of years, I am trying to get it in working order.

The truck ran ok on the rear fuel tank but the front fuel tank no longer worked so I had both fuel tanks and their sending units replaced. Got the truck back and the engine would "stall" (using either tank) very occasionally as though it was starving for gas but then "catch" back up in a couple of seconds.

Had the Dual Function Reservoir (frame-mounted tank selector valve) replaced as well as the high-pressure frame-mounted fuel pump and fuel filter, but the intermittent stalling continued.

A former Ford mechanic who worked on trucks of this era recommended replacing the ECM Relay and Fuel Pump Relay so we replaced both with new OEM relays.

My mechanic kept the truck last weekend and drove it over 150 miles with no problems.

This morning, I left the house, drove about two miles, stopped at a red light, and the engine shut off (not like it was starving for fuel but like I had turned off the ignition).

I then turned off the ignition switch, flipped the tank selector switch to "front" then back to "rear" (no particular reason, just trying anything to get it going again), turned the key and the truck started right up.

I drove on to the grocery store then home (a distance of about six miles), and the truck ran fine.

The mechanic has no further suggestions concerning this intermittent "engine dying" and the best suggestion I have seen from reading online is to check all ground wires (not yet done).

Any helpful suggestions from the forum would be much appreciated.

Thank you.

 

I drove the truck last weekend and the engine died when I stopped at a red light about three miles from home. I was able to start restart it immediately and drove about 1/8 mile then the engine began to die as though it was running out of gas. I patted the gas pedal and the engine caught back up and ran normally the rest of the day. Talked with the mechanic today and his only thought is one or more of the injectors may be clogged from debris that traveled through the fuel lines before the corroded gas tanks were replaced. I guess this is a possibility but I thought the fuel filter's job was to trap such debris so it did not get into the engine. Regardless, the issue now is to replace the injectors or try cleaning them with some type of chemical or gas additive. Anyone had any positive results with injector cleaning or is replacement the logical choice since the truck is 26 years old? Thank you.

 

You could try a bottle of Techron in the gas. Can't hurt.

 

Good recommendation. I used Red Line SL1 injector cleaner in the past and had good results so I purchased a bottle of Red Line SL1 yesterday, put it in the rear tank then drove the truck about 25 miles with no symptoms of being out of gas or the engine dying. Left home in the truck today, drove about six miles then the engine "stumbled" (but did not die), and caught back up. The engine lightly "stumbled" again (did not die), in about 1/8 mile. caught back up and ran normally the rest of the way home, a total distance about 18 miles. Could the "stumbling" be the result of debris that was released by the action of the Red Line moving through the injector(s)? If yes, maybe I should try to burn the rest of the gas in the tank before deciding on whether to replace the injectors. Concerning injector replacement, LMC Truck is pricing new injectors at $100.00 each and RockAuto is offering new Motorcraft injectors at $80.00 each. FuelInjectorWhse is offering reman injectors for $40.00 including a $10.00 core charge. Any of you have any experience with reman injectors or is replacement of the injectors a large enough job to justify only use OEM parts? Sorry for the long post and thanks for any help.

 

I don't have any issues with reman injectors. They are pretty easy to change.

 

Ok. Now about the "pretty easy to change" part. I have done simple work (replacing alternators, starters, brake boosters, serpentine belts, etc.) but never injectors. It seems the most challenging part of replacing the injectors would be removing / correctly reinstalling the various wires and hoses connected to the upper intake, correct? Also, the valve cover gaskets are leaking so I assume it would be wise to replace the valve cover gaskets at the same time the injectors are replaced? Sorry for so many questions but I am learning. Thank you.

 

Since my wife was going to the gas station this morning to fill up her vehicle, I followed her in the truck so I would have a ride home if I was unable to restart the truck when it quit which I fully expected it to do. The truck started right up when cold and ran fine for the short drive to the gas station. I left the truck idling while fueling her vehicle. When I put the truck in gear to leave the gas station, the engine died. I restarted the engine and drove about 25 feet and it died again. I restarted the engine and as it began to die I pumped the accelerator pedal and it coughed and sputtered as I pulled into the street. I continued to pump the gas pedal and about 25 yards down the street the engine caught up and ran normally for the two mile drive back to the house. Bottom line is when the truck runs, it runs fine but every time I drive it, at some point, the engine will die (or try to). If I am able to restart it and keep it running (which I have been able to do so far), the engine runs normally for the trip back to the house. I have only basic mechanical skills and less automotive knowledge but I simply do not understand why this "engine dying" occurs once every time I use the truck. Maybe if I continued to drive it after the "dying" occurs, it would die again but so far I have been too disgusted to drive it anywhere but straight home to avoid getting stuck with a large wrecker bill. Could there be an issue with the fuel pressure regulator or one of the engine control modules that would cause this behavior? I'm just trying to not overlook anything before jumping into replacing the injectors because it seems if one or more injectors were bad that they would be bad all the time and not cause the one-time-per trip engine dying that I am experiencing. Again, thanks for any helpful suggestions.

 

Have you replaced the fuel filter?
If not, why not?

 

^^^^

 

Yessir StrangeRanger, as GLC notes, the fuel filter was replaced early on in this process. Could something have been done (or not done) during install of the new gas tanks that causes an air lock / vapor lock in the fuel line when the truck is started after sitting for a day or so and after the air lock / vapor lock works its way to / through the engine, the truck then runs normally? Just guessing as I am sure you can tell. Thank you.

 

Since it happens on both tanks, whatever it is that's wrong must be either in the dual-function reservoir or in the line from the reservoir to the injectors. Since it's intermittent it's very unlikely to be crud in the injector screens or an issue with the fuel regulator - neither of those tend to get better spontaneously.

I'd almost bet there's something in the reservoir that is either malfunctioning or is not hooked up correctly

 

The dual function reservoir was replaced within the last forty-five days but I understand new parts can be bad, or as you state, installed incorrectly. I did keep the old reservoir, partially disassembled it, and found an o-ring had apparently come off one of the supply check valves and allowed it to fall back into the reservoir body as you can see in the this photo:

There never was any resolution as to where the o-ring went and I have wondered if the o-ring (or bits of it) were lodged somewhere upstream of the DFR. Would it be feasible to disconnect the feed line from the DFR to the engine and snake a small wire up through the line to see if there are any obstructions? Guess we could go from the upstream side of the DFR to the downstream side of the fuel pump then from the upstream side of the fuel pump to the downstream side of the fuel filter and finally from the upstream side of the fuel filter to the engine - whew! Would this help to clarify if the line has an obstruction? Thanks again.

 

Update - All eight injectors have now been replaced with remans and the oxygen sensor has been replaced with a new part. The mechanic is driving the truck home tonight and back to work in the morning (about 70 miles round triip) and hopefully the very intermittent "starving for gas" problem will be gone. We will see.

 

Another update - The truck ran fine during the mechanic's test drive per my post #13 to this thread. Later in the day after he drove the truck back in to work, he had a few minutes to "drive the truck around" and the engine died while he was stopped for traffic. He was able to re-start the truck but said it "ran very rough" which he diagnosed as an electrical problem, not fuel related. He replaced the distributor, drove the truck around the neighborhood (I was with him), and it seemed fine. I brought the truck home, drove it yesterday (including about 30 miles on the interstate) and it ran fine. Problem solved? I think so but something has happened that I cannot explain. When the "starving for gas" problem first appeared (this was the original problem before the "dying" problem), I noticed the temperature gauge needle was slightly right of center though it had always run slightly left of center since I purchased the truck. I asked repeatedly about this and was told "not to worry if the needle was anywhere in the normal range on the gauge" (the radiator and radiator cap had been replaced not too long ago). I finally gave up and just drove the truck with what I considered to be a mild overheating condition. However, now, the temperature gauge needle is slightly left of center and remains there even if I am stopped in traffic. It seems unlikely the repairs that have been done (replacement of the gas tanks / sending units / dual function reservoir / fuel pump / fuel filter / ECM relay / fuel pump relay / injectors / valve cover gaskets / oxygen sensor / distributor) could or would have any bearing on the engine temperature - or am I missing something? I am glad the truck is now working but am uneasy not knowing why. Any helpful comments are appreciated.

 

So it ended up being the distributor? Have you replaced the sensor for the gauge?