86, F150, 5.0, EFI dual tank fuel system problem
 

I have been struggling with this for quite sometime now. What would help me most is a wiring diagram and/or fuel system component lay out. This 4x4 has dual tanks and I don't seem to get fuel from either tank. The fuse for the fuel selector circuit had been pulled by someone, no idea why or when, but wonder if they took anything else out. The front (high pressure) fuel pump in the frame cycles normally, but I don't seem to have any action from the low pressure pump in either tank. I also am not reading any fuel in either tank. One tank has at least 5 gal, other closer to 9 gal. I can get the engine to start for short durations once in a while, but nothing sustained.

Someone please help!. I need this transportation despirately due to the death of our Explorer 2 weeks ago.

Thanks.
Dale

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Welcome aboard c150L. you will find dozens of post on what I call junk fuel systems on this board, by searching you will find many many ideas. I have posted a couple of times what I have done. If the high presure pumps work then my guess is tank pumps have failed or the switch over valve is not switching over completely. One other thing there should be two pump relays one for tank pumps and one for high presure. I can't remember for sure on that, but for some reason I remember that. I worked for a Ford dealer in 83-84 and these fuel problrms seened to never stop coming in.

See if you're getting power at the tank selector switch in the cab. It should be a red wire with a yellow tracer (stripe). If you are, move to the pumps. There should be a brown wire with a white tracer or a solid red wire. If you get power there, the pumps are shot. If you don't get power there, or at the switch you can also try and power the pump with a jumper wire, but be very carefull. Sparks and gas fumes don't mix well. It's best to hook the jumper to the pump lead, then to 12v power.

From the switch it goes upstream to a pink wire with a black tracer into the inertia switch. The Pink/black wire feeds the High pressure pump.

Again be carefull.

Hope this helps,
David

Web page in my post? I don't see one, but can not post a reply. HUMM.

Hey guys, thanks for the welcome and thanks for the tips. I hopefully can get to this thing this afternoon again.


Thanks again,
Dale

Comment on second relay. I was wondering on such. Not sure how many connections are on the back of the selector switch in the cab, but seeing that one switch has to control pumps and the fuel gauge, I might have expected another relay that actually does all this switching. Wire colors does give me something to start with though. I just find it odd that I show no fuel in either tank and (seemingly) get no fuel pump action from either tank. That's like 4 things that all went out while this truck was on vacation. (Tranny was out.)

Just wished it were not winter out here. Bad enough tracing such problems, but doing it out in the cold is like icing on the cake.

Thanks,
Dale

Check your grounds. I believe that the pump and sender grounds to the same place. Also check for a disconnected harnes / broken wires...

There should be 6 wires on the selecter switch. R-Y - power in, BK - Ground, R and BR-W power to the pumps, Y-LB and DB-Y gauge signal.

David

Thanks for the more info. it all helps a lot. Just one clearification. In my mind, I see a DPDT (double pole-double throw) switch in the dash. What confused me is the BK wire which was stated as ground. I picture that one going to the fuel gauge and the y-LB and DB-Y going each to a tanks level sender. Not sure how the following will appear, but here goes. I may also have the F/R tank indicated wrong and the actual position of wires wrong. I'll correct when I see actual. Diagram, if all lines up, showing the rear tank and sender selected.

R---- R tank pump--------o| |o--R tank sender-Y/LB
R/Y--- pump supply-------o| |o--fuel gauge ---BK
BR/W-F tank pump--------o| |o--F tank sender-DB/Y

(Board says I can edit my posts, but have no edit button.)

Finally got to the switch. Power in (R/Y) goes hot when the main fuel pump kicks in. Resistance on both wires to the tank pumps about the same. 36-37 ohms. Appears pumps are both there and are both grounded. Suspecting both pumps are seized up from sitting? (Has to be that "Kwik Trip" gas my wife won't stop putting in our vehicals. (In case you don't know what Kwik Trip gas is. CRAP!)

R---- F tank pump--------o| |o--F tank sender-DB/Y
Pk/Bk- pump supply-------o| |o--fuel gauge ---BK
BR/W-R tank pump--------o| |o--R tank sender-Y/LB

One sending unit reads about 70 ohms, the other 126 ohms. If I ground out the center wire (BK) my fuel gauge goes to full. Suspecting that 70 ohms is not enough to bring the fuel gauge above empty. Anyone know what ohms a good sender sends to the gauge?

c150L

Re: (Board says I can edit my posts, but have no edit button.)

I think that you only have an hour to edit your post, then it gets locked out.

David

Couple things that I'd do next is make a jumper and go from the tank sender (70ohm or 126ohm) to the BK wire. See if you get a reading. 0 ohms appears to be full, so more than 0 is less then full. I would guess that 70 ohms should read something. Go to radio shack and get a couple resisters, say 10, 25 and 50ohms or something like that and put them between the ground and the BK wire. It should read something less than full.

Back to bypassing the switch, if the fuel levels show up, try and jump the power. If the pumps work then it's the switch.

David

I bypassed the switch (pump side. No pump action. I hooked up a remote starter switch to hot and to the front pump wire (assuming red) crawled under and hear nothing from tank with I hit the switch. I'm pretty sure the pump is seized up. Guess I'l have to drop at least one tank and change the pump. While there, perhaps I can resurrect a fuel level sender. (Don't think that's part of these pumps.

I'll have to take the guess that 70 ohms is a bit less than empty. This front tank came up about 1/2 a needle width higher than the rear tank, below empty.

The senders are known for going bad. Mine only reads the top half of the tank. F is full, E is about 1/2 tank.

The pump is mounted on the sender unit, but can be replaced seperately, or as a unit.

I have an unconfirmed report that there's a filter between the tanks and high pressure pump. Look for a black round thing that the tanks are connected to. It's covered by a shield but is mounted on the left frame rail. Pep Boys gave me a Purolator filter # 50126 for it. I'm planning on replacing mine because I have low fuel pressure. I'm propably going to replace the tank pump too, so I'm right there with you in reguards to fuel problems. Why can't they happen when it's 75 outside?

Anyway I'd replace the tank strainer, and both filters (canister and inline) while you're under there.

David

What is with all these 86 F150s that don't run? LOL/

Finally got this whole fuel delivery system figured out. I jumped power to the tank selector switch connector and found neither low pressue fuel pump in either tank would run. Today, the rear pump would run, put in more gas but still no sustained runs. Removed the selector valve/canister. This is mounted in the frame rail between front tank and the high pressure fuel pump. This canister switches itself depending on which tanks low pressure pump is supplying it. Tore it apart and found it still in the front tank position and the canister type filter on the bottom is plugged. Have to get a new filter. I also set the top section to supply/return from/to the rear tank. This is the one that the pump is working in. Think that perhaps the rear pump is weak and/or there was a big bubble in the system and with the plugged filter, the valve would not switch switch itself. In my cheap, one step at a time deal, I'm putting it back together as soon as I get a new filter to see if it will sustain running on the rear tank. Then I'll work the problems out of the front tank. If the canister valve won't switch from front to back,then I'm going on the belief that the rear pump is weak and needs a change out.