marine6531

Hello everyone! After a search I have come up with nothing for my problem. I have an '86 F150 EFI 5.0L with about 85K miles, dual tank 2wd that will no longer start. About a year and a half ago I had to change the rear fuel tank due to massive amounts of rust. I also changed the sending unit and fuel filter in the DFR. Ran fine for a while then started running bad so I bypassed the DFR and ran a small, clear inline filter (like what you would put on a lawn mower or atv) and again, ran fine for almost a year.


Early this year is started stuttering under load. Idled good, but when I accelerated it stuttered a little, got worse in 2nd gear, so on and so forth. A few months ago I replaced the high pressure pump on the rail, fuel regulator, ignition module, and installed a new fuel filter. This time I bought a bigger inline, like what would go on a Bronco or newer F-150. The plugs, wires, cap and rotor were also replaced late last year. Still stuttered, no change in performance. Well, a month or so ago I went out to crank it up and it ran for about 10 seconds and then died. Won't start no, it acts like it wants to from time to time but it won't, even with starting fluid. I have put fresh gas in it, nothing. I have spark and air, but the way the fuel comes out of the shrader valve makes me wonder if I have an air leak in the fuel line, or if the fuel filter is to big, wrong, something. And the filter is flowing in the right direction. Also I have rubber fuel line spliced in with the OEM plastic lines, no fuel leaks anywhere, I can hear the high pressure pump but not the in tank. My hearing is bad though.


I remember the small, clear filter being almost half full when the engine was off, and mostly full when at idle. I cannot see into the current filter. Would internal capacity be too big? Or maybe the filter not being level? The rear of the filter is lower than the front. This paragraph may be completely irrelevant, but I wanted to throw out any possibility.


I have also thought about maybe the high pressure pump sucking air in through the new connections in fuel lines around the filter. Being the suction is most likely stronger than the pressure of the in-tank pump, it sucks air in with more force than the low pressure pump can produce to force fuel out. This may also be a stupid theory.


Sorry for the thesis, but I wanted to include all the pertinent (well, what I think is pertinent) information I could. Any thoughts or ideas would be very much appreciated.

marine6531

Forgot to mention, I also pulled the distributor to check the gear in case it was worn out. It's good.

JayzDaddy

Welcome to the forum.
Your in tank pump is designed to just get it flowing. Your external pump builds your 40-50 psi you need. Now you say you have air and spark. Im assuming at the plug. Do you have fuel to the rails? If yes i would say check pressure there. If thats good your injectors may be bad.

If no fuel at the rail how about disconnecting electrical to the frame pump and then pulling fuel line loose from the tank side. Stick the line in a bottle or such and cycle the key on for 3-4 seconds, then off. Check the bottle. If there is a decent bit of gas you have a bad frame pump or a blockage. Bad meaning it may run but not make required pressure. If you have no or very little gas in bottle your rear pump is not getting voltage or is bad.

Also check for codes. Shove a test light in the little grey rectangular plug laying on your drivers fenderwell and connect your wire end to the negative terminal of battery. Your check engine light will flash codes. Count the flashes. 1set, pause, then 2nd set. Each set makes a number. Put the 2 together for a double digit code. There will be a longer pause between codes.

marine6531

I have spark at the plugs, checked that with a spark tester. There isn't much fuel getting to the rail. Lots of air comes out with some fuel when depressing the shrader valve. The high pressure pump, I replaced 4 or 5 months ago. It is an autozone part (duracrap) so that could be a problem in itself, the in-tank pump is also from autozone. I will try the bottle after lunch. Thank you for the tips! I'll check back a little later.

JayzDaddy

No problem. With these old trucks wiring issues can be a pain to trace but everything else is pretty basic. Just simple process of elimination at certain junctions. But these are a breeze compared to the 97- roughly 04/06. Lots of these will give you an idea of the problem but not exact. The old ones like i said just eliminate the junctions. The new, new ones will pretty much tell you the exact issue but are stuffed under smog, hoses, and wires, requiring a small Chinese midget to fit in there to work on simple fixes (no offense to chinese midgets).

klricks

Explain how you bypassed the DFR.
If done correctly:
- You can only use 1 tank and the dash switch must always be set to that tank. (tape it or do an electrical bypass).
- The corresponding fuel return line must be bypassed as well.
- All open ports on the DFR need to be blocked

Johnboy429bbf

I had this problem out of a 89. Gas keep running from one tank to the other. And cause alot of the same symptoms. Pulled all the lines blew them out with about 30 lbs of air. And ended up blocking of the rear tank to get it to stop, got rid of the truck before I got really tear in to it

Deputy739

Check the exhaust, it could be stopped up.

hmg1971

I have an 83 that was doing the same thing. I chased it for 3 days and it was a bad coil. Something simple but I was focused on plugs, wires and the fuel system. Might want to give it a shot.