My 1986 F-150 XLT will crank but will not start. I have spark and I changed out the fuel pump in the front tank and the in-line fuel filter but it still seems like it is starving for fuel. I recently eliminated the rear gas tank due to leakage. Flipping the fuel tank switch makes no difference.
Any suggestions????

 

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What motor? fuel injected?

 

Good call Andy - we need to know CARB or EFI.

The systems are wildly different for t-shooting purposes.

-HOWEVER (comma): Since the rear tank was disconned be reason of leakage, it qualifies as the last thing done on it. Is it possible a line is disconnected that should not be, tank switch stuck in wrong position, or leakage of air into one of the fuel lines?

I ALWAYS go back to the last work done on a machine and look for any connection with a recent problem before moving on to other likely causes.

You'd be amazed how many times I've struck pay-dirt that way.
You have to admit there's a coincidence here: Both involve fuel system.

~Wolf

PS: Could also be a worn transfer valve that allows air to pass from the open lines. Test for this possibility? Jam a golf tee into the two lines for the rear tank. Allow time for the fuel pump to pressurise the lines and watch for leaks.

 

The 1986 F-150 is a fuel injected XLT 4X4 with a 302 engine and a longbed. The engine does start momentarily when I spray starter fluid directly into the air intake. Also, I do hear the external fuel pump running when I turn the key to the "on" position. I checked the inertia switch and it does not seem to need reset. I'm running out of ideas!

 

with fuel injection there is no external fuel pump. Now with that said here are a feww things to check. 1 check the fuel pressure in the fuel rails. if it is too low or nonexistant then the truck won't start and could mean either there is a leak in the line somewhere or the pump is bad. even though you just put in a new one it could still be bad. Or maybe a bad gound. Check and clean all your connections. But the other thing you should check if your fuel pump relay. It's located on the driver side fender. they have a tendancy to fill up with water and short out. And when they go bad the truck might start and run until the water moves the right way and kill the truck and if your lucky it'll start up and run again or itwon't. I hadthis problem with mine. And another if you checked all of that and you still have the problem start checking that fusible links in wiring harness one or more of those could be bad a give you your problem unlikly though but possible. hope this helps . and start simple and check fuel pressure and then your pump relay first.

 

One thing I haven't seen mentioned yet is the in-line fuel pump by the tank switching solenoid. I have seen the wires knocked loose by accident, or the pump may have just died.


The tank fuel pump is a low pressure pump just meant to help the gas "get" to the in-line pump where it gets the required pressure to shoot through the injectors. You need both pumps working.

To see if it is at least trying, just have someone turn the key to "run" not "start" while you listen next to it. It should run for a couple seconds when you first turn the key to run to build up pressure. It then quits running until it gets the required signals as the engine turns.

The pump is just under the drivers door on the frame rail. It is possible to jumper the code plug to make it run constantly but you usually don't need to go this far and I don't recall which pins you jumper off the top of my head.


FWIW - I don't think this next item is your problem but if you start messing around and take you tank switch solenoid apart, there is a filter in there too that is likely original equipment. No one ever talks about it and they were designed to last forever but they frequently get gunked up eventually and cause a lack of power. It is like 3 bucks at the auto parts store. It is a cartridge style filter that goes in the bottom of that switching mechanism. ( the bottom unscrews and the filter sits in the bottom.)

My bet is you will find your inline pump dead or as Greywold said, you are sucking air from the line you disconnected from your rear tank.

Good Luck,

Lee