I recently helped my son purchase a real slick straight 91K, 1986 F150, had to have been garage kept most of it's life. see the picture , any how I AM NOT a Ford man, thus I am lost with this one. the problem - she seams to be down on power, and occasionally (more than not) wants to buck at highway speeds, as if the fuel filter is plugging up. the thing is the only thing between the tanks and the fuel rail is, the tank selector and the main fuel pump. Yes I know there is a boost pump in each tank, but where is the blinking filter, or where should it be??? also any Ideas of what to do to get the power up where it should be? if it were a GM I would have been all over it LOL! also can we pull the cats with out effecting the ECU??

 

ok first of all, lets start with two VERY important details, what motor do you have? my 86 has a 351W, which is carbed, and has a mechanical fuel pump.

next, and this is also very important, has the motor had a good tuneup recently? being that low a mileage, if its indeed fuel injected, I would take the fuel injector(s) off, and have a shop ultrasonic clean, and flow test to ensure their function is proper.

a carbed motor is MUCH simpler, since their fuel pump is on the front left side of the engine, directly under the distributor, and thats USUALLY where the filter is on that system.

 

OK! yep it is a 302FI, the first year I am told, and I was worried that someone would say "Injectors" they don't look fun! I seem to remember that "some" EFI systems put screens at the injectors and called it good for a filter, I don't rember which MFG did this? and We havent gotten to the tune up yet, I have experienced (more like bitten in the keaster) by a bad ign rotor before. can you say "timing chain for nothing". I havent had much exposure to Ford's but what few there were ?????

 

Correct, 86 is the first year they made EFI. I second checking out the injectors, but an easier thing to do is check the plugs out ect. just the simple things, rather than pull off all the injectors and end up having it be something simple.

Secondly, cutting off the CAT should not affect anything as long as the oxygen sensor is left intact. I believe 86 had the O2 Sensor, i know my 85 does.

 

cool! on the cats, also I do plan a complete tune up, but back to the problem does this truck have a fuel filter?? there is a line from the tank selector to the fuel pump that appears to be a tad to long, and newer and more flexible than the rest of the lines. did someone remove the filter????

 

i believe that they are supposed to have a fuel filter inline, i know my 87 302 does, which is EFI, but my 85 that is carbed does not, so my guess would be that it should have the inline fuel filter that lies against the frame, it should be in between the tank(s) and the motor if i remember right

 

There is a fuel filter inside the switching valve. Ford call it the dual function reservoir. If that filter is plugged then you will get the engine cutting out or 'bucking' at higher speeds. Also the high pressure pump on the frame rail will whine loudly when starved for fuel for any reason.

You have to unscrew the bottom section of the DFR to get to the filter. Ford says that is a lifetime filter but I had to replace mine 2 or 3 times before I canned the DFR and installed an electric switching valve.

Both of the in-tank low pressure pumps must be working in order for the DFR to function. If not you can get fuel transferring from one tank to the other and other problems. In my case the rubber connecting tube inside the tank on the sender, disintegrated and let gobs is debris enter the fuel lines and jamb up the DFR valves and filter.

There also may be a filter just in front of the HP pump on the frame rail but not all trucks have it.

For more fuel system info see my writeup.. link in my signature...


.