Hi all, new member here, I have been searching around a bit and haven't seen this exact problem ... or maybe it is a combination of problems.

I have a 1987 F150 regular cab 4x4 that I just purchased (recently painted so no decals or emblems on the sides so cant tell you exact model) it is a standard cab, 6 1/2' bed, dual tanks
#1 - no matter what position I put the tank selector switch in, the truck is running off of the front tank.
#2 - no matter what position the tank selector switch is in, the fuel gauge reads empty ... not below empty, just empty

If i turn the switch to on and have my son under the truck listening he says he thinks he only hears the front tank fuel pump no matter what position the switch is in.

I have taken the tank selector switch off and tested it with a multimeter and it seems to test fine

I have not been able to find a good wiring diagram for a '87 f150 fuel system but I found one for a '86, I checked voltages and I got 10.7v (not 12+ ??) to ground through the switch at all the right places and I get about 1.7-1.8v back from tank going to gauge.

I do NOT have fuel pumping from one tank to the other (thank goodness)

If I disconnect the dash fuel tank selector switch completely and then turn the key my fuel gauge reads above full (this indicates gauge itself is good .. right?)

I realy hope someone has an answer for this one, it is driving me nuts.

 

Your VIN is 1FTEF14ecHps##### . The "e" is the engine code: Y=4.9L I6; N=5.0L V8; G or H=5.8L V8; L=7.5L V8 . The "c" is the check digit: 0-9, or X . The "p" is the production plant code. The last 6 are the serial number: A or B followed by 5 numerals. It should be stamped into a metal tag at the front edge of the dash pad forward of the steering wheel, visible thru the windshield from outside.

The dash switch selects the in-tank pumps, but the pump on the frame rail runs either way, so that's probably what he's hearing. Unplug it & jumper the Fuel Pump Relay terminal in the DLC (under the L hood hinge) to ground so the tank pump runs continuously with the key in RUN. Then switch to the other tank to check that pump.



Those dash switches are known to go bad, so don't be surprised if you eventually replace it. NAPA & PartsPlus+ stores carry an aftermarket direct-replacement switch.

Fuel level senders are also known to go bad, as are the wires & connectors along the frame rail. Unplug the fuel tank connector & the gauge SHOULD peg past full. If it doesn't, then the circuit is shorted to ground somewhere between the dash switch & that tank. If it does, either the level sender is bad, or the float is sunk. Check the 2nd tank the same way.



The low voltage on the pump circuit suggests corrosion inside or on the terminals of the inertia switch. The terminals can be cleaned with brown paper or a pink eraser, but if the resistance is inside the switch, replace it.



The '84-89 system doesn't transfer fuel between tanks - that's '90-96. Click my black Bronco in my sig & read the captions in the '84-89 Fuel Reservoirs album.

 

Rear in-tank pump is not working to change the selector valve.
You may have bad wiring for both the pump and the sender from the selector to the tanks.
Or both floats have sunk in the tanks.

He is hearing the frame mounted high pressure pump.
When working in the fuel system always use a test light and not a meter as you will get wrong readings with a meter and you will go around in circles all day with a meter as it does not load the circuit.
You do not get any current back from the tanks, they only take the current to ground through a motor for the pump or resister for the gauge.

Here is a diagram:
http://i54.photobucket.com/albums/g9...-88FSeries.gif

When this happens it always goes to the front tank but your selector valve is locked in the front tank position so you will not get it right now. It is the return fuel that goes to the wrong tank on a 1987 as the “O” ring will stick on the tank return valve from not being used.
Right, your gauge is OK.

 

Having similar problems with my 95 f150. Have power to front tank pump but no guage. Rear has no power to pump or guage. Move switch from front tank to rear tank the trucks dies. Can't tell what tank the fuel is returning to because the guages don't work. Got a new wiring harness from the fire wall to the tanks but have not installed it yet. Should have tried replacing the switch first before buying a harness. The switch is a whole lot cheaper than the harness!

 

Sounds like you do have a bad switch.

 

ok, retested the dash switch it is definately good.
did resistance checks on the tank senders ... they are both at 21.8 and 22.3 ohms so both floats must be at the bottom ... gotta see about getting new floats or probably just new sending units ... if i have to drop the tanks i might as well do it right.
also, the front tank pump resistance is about 18 ohms ... about right for a small pump motor but the rear tank pump resistance is infinate so have a bad real pump.
no matter what i could not find the inertia switch to make sure i didnt have corrosion on the contacts there. someone sent me picture of it showing it on the passenger side right in front of the door but it is not there ... who knows, first steps are the senders and the bad pump then i can find out if the switching valve is bad.

thanks again for all the help, will let you know what happens. hopefully the napa i go to today has the parts.
the other napa didnt have a clue what i was looking for.
by the way, with the 6 1/2' bed what size is my side tank? is it the 16 gallon or the 19 gallon, i think those use different sender units and i want to buy the right one .. hopefully i can get an answer before i go into town in a few hours so i can get the right one.

 

The location of the inertia switch on your truck:


/

 

Late-80s inertia switches can be where subford's diagram shows, or just R of the tunnel.

I thought I had a chart of fuel tank sizes, but I can't find it.

It may be easier to lift the bed off than to drop the tank, so consider it.

Fuel level senders are available from Ford & PartsPlus+, but these PNs may not be current.

TSB 88-18-03 Fuel Gauge Erratic

Publication Date: AUGUST 31, 1988

FORD: 1987-88 MUSTANG, TAURUS
LINCOLN-MERCURY: 1987-88 SABLE
1988 LINCOLN TOWN CAR
LIGHT TRUCK: 1987-88 BRONCO, F-SERIES

ISSUE: An erratic fuel gauge needle when the fuel tank is 1/2 to 1/4 full may be caused by excessive wear of the resistive film on the fuel pump sender assembly. The wear occurs during transporting of the vehicles via rail or truck over long distances. The fuel gauge will indicate correctly from a full tank to about 1/2 or 1/4 tank of fuel. When the fuel gauge needle is below the 1/2 to 1/4 tank range the needle will swing all the way above the full mark on the fuel gauge.

ACTION: To correct this, install a new fuel pump sender assembly. Refer to the appropriate 1988 Car/Light Truck Shop Manual, Section 24 for detailed service information. Refer to the following fuel pump sender application chart for the correct service part number.

Fuel Pump Sender Application Chart
Model Year Application Engine Tank Size Service Part
1987-88 Mustang 2.3L./5.0L All E7ZZ-9275-A
1988 Lincoln Town Car 5.0L All E8TZ-9H307-G
1987-88 F-Series/Bronco 4.9L/5.0L All E9VY-9275-A
1987-88 Taurus/Sable 2.5L 16.0 E8DZ-9H307-F
1987-88 Taurus/Sable (W/ Tripminder) 2.5L 18.6 E8DZ-9H307-E
1987-88 Taurus/Sable (W/O Tripminder) 2.5L 18.6 E8DZ-9H307-A
1987-88 Taurus/Sable 3.0L 16.0 E8DZ-9H307-C
1987-88 Taurus/Sable (W/ Tripminder) 3.0L 18.6 E8DZ-9H307-D
1987-88 Taurus/Sable (W/O Tripminder) 3.0L 18.6 E8DZ-9H307-B

PART NUMBER PART NAME
E8DZ-9H307-A Fuel Pump Sender Assembly
E8DZ-9H307-B Fuel Pump Sender Assembly
E8DZ-9H307-C Fuel Pump Sender Assembly
E8DZ-9H307-D Fuel Pump Sender Assembly
E8DZ-9H307-E Fuel Pump Sender Assembly
E8DZ-9H307-F Fuel Pump Sender Assembly
E8TZ-9H307-G Fuel Pump Sender Assembly
E7ZZ-9275-A Fuel Pump Sender Assembly
E9VY-9275-A Fuel Pump Sender Assembly

OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under Basic Warranty Coverage

OPERATION DESCRIPTION TIME
881803A F Series Aft Of Axle Tank 1.2 Hrs.
881803A F Series Midship Tank 0.9 Hr.
881803A F Series Both Tanks 2.0 Hrs.
881803A Bronco 1.2 Hrs.
881803A Lincoln Town Car 1.4 Hrs.
881803A Mustang 0.9 Hr.
881803A Taurus/Sable 1.0 Hr.

This is the current PN for all '96 Broncos.

 

Hey all, I'm about to come into possession of my dads '87 F150 XLT and it has the problem mentioned above.
I'm eager to get to working on fixing the problem, only issue is the truck is in MN and I'm in TN LOL.

The truck runs just fine on the rear tank, but when the in cab switch is moved to the front tank the gauge shows the front tank level, but the fuel is still being pulled from the rear tank.

My brother-in-law took the truck to a mechanic friend of his and he said the "switch" on the frame is bad (I'm assuming he meant the valve that switches tanks) and the only one available to him costs $108. That seems a bit high.

At any rate, my mom is meeting me halfway between TN & MN so I can get the truck and it will be driven on the rear tank only.

My question is this. It looks like AutoZone has the valve available, but they list 2 models. One with return lines and one without. Without getting under the truck is there any way to know which one I should get?

Also, since gas is still pulled from the rear tank, even with the switch set to the front, should I assume the low pressure pump in the front tank is dead?

The truck actually sat for about 2 years with minimal run time, one of the first things I'm going to do when I get it home is drop both tanks, empty and clean them out. While the tanks are down I will replace the fuel level sending units (I know the rear one is bad, it always has been). Would it be smart to go ahead and replace both low pressure pumps, just in case?

Thanks
BTW, the truck has the 5.8L V8 engine (351? IIRC)

 

The Switch at the auto parts store will not work.
The front pump could be bad as the selector valve is pressure switched or the electrical to the front pump may be bad.
The selector valve may be frozen in position of the rear tank.

 

the vavle only switches once that tanks pump builds pressure, so you really need to verify the front pump is pumping, then that would show the valve is bad. I pulled the plug on the frame pump then grounded the test lead for the tankl pump to verify mine.

 

That's not possible unless someone crossed the wires from the front in-tank pump back to the rear. And fuel is 'pushed' out of each tank - not 'pulled'.Yes, read the last sentence in post #2 of this thread.It's not if 1) you need it (which I doubt), AND 2) the valve is new, AND 3) it actually works.If they were the only place on the planet that had it, I'd make do without it. Never buy anything there - not even rags.I wouldn't. The correct pump is expensive, and aftermarket pumps aren't as reliable as OE. Fix what's broke - leave everything else alone. But you might soak the bed bolts' nuts with penetrating oil, pull them off, & apply anti-seize so you can lift the bed next time.

 

I have a similar problem with my 87 except its always registers over full. And when the tank gets down to about a 1/4 the hand will flop back and forth. but when my truck is on and sitting still it registers full and when i press the gas and start moving it flops back and forth from full to empty

 

Open circuit in the level sender. Replace it.

You can try to disassemble the rheostat & bend the wiper to make more contact pressure, but I'd have a new sender in-hand in case it still doesn't work.

 

Steve,
Now that I have the truck a couple of things. I do believe my truck "pulls" the gas out. It is a 5.8L carbureted engine and has a mechanical pump on the engine.
Also, I found out that when the 3 port tank selection valve either fails, or does not have power to it, it will default to the rear tank. My mom actually ran out of gas since someone had flipped the tank selection switch to the front tank, that's the one she thought she should fill. She only put in 3 gal of gas, drove about 200 feet then the engine died. The garage she was towed to said she was just out of gas, use the rear tank only.

I have disconnected the valve and verified that when 12vdc is applied to it, it will not operate so, indeed the valve is bad. I did find an OEM replacement for it and it will be arriving any day now.

Here is picture of the valve in question (and yes, it was fun to take off with all that rust!)