My rear fuel tank sender pegs the fuel gauge past full mark (always) - which at least tells me that the sender is working and most likely it "has a bad ground" from what I have read.

I was just under the truck and I see a small wire loom coming down the front of the tank with the split plastic covering, I assume from the fuel sender and it apparently it goes into the tail light wire loom?

I am assuming that the sender itself has a ground terminal and a ground wire in this loom?? A friend told me that I just have to ground the tank itself to the frame with a new wire. I was hoping to just clean up a ground connection to the frame or easily install a new ground wire...?

Access is terrible at that visible loom from the sender. I can't drop the tank now (don't want to) and because it is full and PLUS I have a spare tire mounted under the rear tank and the mechanism that holds the tire up is all messed up so it's going to be a job to get that off and fixed. I found my 21mm wrench still hanging from an upper nut from a couple of months ago when I tried to remove it.

I was hoping that I could just clean up a ground connection or install a new ground wire but the tank is not coming down until next year (unless I have no choice). Rainy season (cold and wet) is coming soon and this would not be a fun project in that weather. Both tanks must come down next year for full cleaning/maintenance though.

The gauge doesn't work at all from the front tank but that tank sender is more accessible to test and it appears to be much easier to drop the front tank..? compared to back tank?

I want one gauge working so I won't feel like an idiot if I run out of fuel somewhere, especially with a grumpy passenger.

It was in California or here in Washington State or both States, that you can be fined for running out of fuel on the highway. (maybe on any roadway).

 

Two things:
1. Whether your gauge works or not, you can gauge fuel left by using your trip counter to record when you fill up or switch to the other full tank. I do this myself -- I know I can do 200 safe miles on the rear tank and 260 on the front tank, so I switch tanks(and reset the counter) when I get to that number and fill up at appropriate times.

2. Rear tank isn't that hard to drop, empty at least. Basically, you remove the tire, get those parts out of the way, unscrew the fuel neck from inside the gas cap area, then remove the 4 bolts holding the two halves of the tank-bash-plate in place. With those out of there, you can wiggle the tank out of it's place, to get enough room to disconnect the wires and hoses. It's a pain, but I've removed and reinstalled the tank by myself in an afternoon.

 

I have heard it is way easier to pull the bed to work on the fuel tanks than drop the tanks. That way you can trace all the wiring as well.

The fuel senders have 2 terminals and each one has a wire in the harness. One is a ground, the other goes to the gauge. I have no clue where exactly the ground wire finds its 'ground' connection...

 

I second the comment about removing the bed. Especially, ifins you are planning on reinstalling the tank. I tried to reinstall my tank with the bed on and the sender wire wasn't long enough to install until the tank was fully mounted. My sender wires were barely long enough for the install with the tank installed and that was accessing it with the bed removed.

If I have to perform a sender replacement again, on the rear tank, I would remove the bed. ***Plus, your bed fastener bolts are probably deteriorated. When I removed my bed, several of the bolt fasteners were severely reduced in diameter and strength due to rust. I had to cut some of the bolts off. Ford doesn't make a replacement, but Tractor Supply's grade 8, with a washer works just fine. I feel much better about the strength of my bed now.

 

<p>actually ford does still stock replacement bed bolts, but they are VERY expensive. around $100 for the 6 bolts and nuts.</p>

 

Just went through removal of both tanks this week without bed off. Front tank, piece of cake, rear tank, little bit of cussing but it is manageable. Putting it back is more of a pain to get to the clamps holding the hose and insert the air vent hose correct to the tank and to the fill up neck, tighten everything.
The sender works, or at least mine does the way when full tank, the resistance is 10 Ohm, when empty, resistance is 73 Ohm. For some reason the rear tank sender reads over the full when full as well, but this could be solved by inserting resistor to the circuit for the rear tank. The front reads fine, just on the F when full. The interesting part is both senders have the same parameters, might be the FSS for switching the tanks.What I want to say, if the two cables are shorted somewhere, along the frame, FSS, it will read over the full all the time. U can manage to disconect the plug from under the truck, with the rear tank in place or at least mine can and measure the resistance of the sending unit. It is tight space over the frame support above the rear diff, but manageable.
The problem with sending units is, they are printed cirrcuit board, and it wears out at the line the arm swings over it. I just bent the arm so it would read on the inner side of the trace where still is the material undamaged. So far it works , I just count on another 30 years before it wears off completely

 

Very Interesting Romel! That reading is almost perfect for the bi-metal type fuel gauge that was installed in the Econoline Vans E-Series! (I think you accidentally reversed "Full' with 'Empty' when stating those resistance readings). With those readings I suspect that you have both a gauge and a fuel sender that was intended for the E-Series vans. The F-Series was quite different with a Magnetic gauge and different resistance specifications from the sender.

Here are the specifications compared, copied directly from the 1987 Ford Shop Manual for Body Chassis Electrical at 33-20-2:

FIG. 3 Fuel Indicating System-Sender Resistance
FUEL SENDER RESISTANCE
Type of Gauge_______Full Tank________ Empty Tank
Bi-Metal____________10 ohms ________ 70 ohms
Magnetic___________160 ohms ________15 ohms
CK10440-1A

WAIT A MINUTE? Are one of those resistances shown for the respective gauge/sender units at full/empty accidentally reversed in the Ford manual? That would indicate that your original statement about resistance readings full/empty is correct and the manual is in error. Another mystery to solve..

The bottom number CK... is probably a reference number.

So whatever gauge and sender you have and whatever you did, it appears to be a very close match to the bi-metal style gauge specifications so that 3 extra ohms could be the difference at 'full tank' that you are seeing on the gauge (or something as yet unexplained if it is a magnetic coil type of gauge with corresponding sender that was supposed to be installed in the 1987 F-series.

 

I gradually made my way back to this topic and I certainly intend to make some replies and add some good information.

I spent 4 hours last night searching through the the extensive official 1987 Ford Shop Manuals (which I bought on CD at Amazon.com for about $30.00 in .PDF format) searching for everything I could find on the senders, gauges, tank selector valves and switches plus the power distribution wiring schematics with splices, connectors, location of ground points, etc. I take a screen shot of every image (which includes the text) that pertains to this subject and I save those images into respective folders for quick reference - because these details are not easy to find in several thousand pages split between 5 separate manuals. I still have hours to go to find and copy all of the cross-referenced pages that will show more details.

Anyway I have some good basic information to post but I can't do that until later because I really need a break!

Thanks to all for your interest and replies

 

I'll post the colors of the respective positive wires and where they run a bit later. I think the two different colored positives with tracers from the respective senders go first to the Fuel Selector Valve and one to it's Switch side and then a different colored positive wire from there to the gauge.

Both of the ground wires from the senders are black wires (All ground wires in these trucks (as from the Factory) are supposed to be black (BK) and I think the main ground connection is behind the driver's side headlight but I'll have to look again to confirm that before post about the wires.
EDIT: The ground wires for the senders go into the Tail Light Wiring Harness and are grounded with the ground wire(s) for the tail lights which should be easy to find
It sure would be nice to only clean up an easy to access ground connection and have a sender or both work! Someone might be so lucky.

 

Thanks for the safe mileage/tank numbers! I would have given that method consideration but I was unsure whether or not my fuel pickup is broken off at the bottom, thus running out of fuel with 1/4 tank left and I wanted to keep the front tank as empty as possible as I had intended to remove it before winter rainy weather sets it. It's too late, it's already here. The only place I have to work on it for bigger jobs is on the grass beside the duplex unit I live in which is in a cramped urban area with small streets and very limited parking. I have too parking spaces on the street with 3 vehicles. During wet season the grass quickly turns to mud where I walk and part of that is on my nice neighbor's property. I think I can get the rear sender and gauge working and use the front tank as a reserve until next year when I can pull both tanks.

My objective is to get this truck ready for a long haul (loaded) over several mountain ranges with a trailer, as soon as the truck is ready (next year) and I didn't want to use the trip meter odometer calculations to indicate how much fuel I have left.

Thank you for that information! By the way I happened on to a couple of your youtube videos quite by accident while I was surfing youtube for something unrelated. I recognized your user name from from here at FTE and glad I had the time to watch those two, because you have been very helpful to me in these truck forums. One was your 0-60 mph and the other, a 7.3L start up on an engine stand. Thanks a bunch for your help to many people in other topics!

 

Months ago I saved some photos from two 'removed bed' methods. PLUS I saved many good comments and other photos from topics discussing this whole fuel senders issue including the sender modifications and fixes and fixes, even etching a new circuit board, etc. I have those in a folder. I wish we had a better way but these trucks are nearing the 'antique' and even the 'classic' categories so I think it is worth the effort. I just see mine as a heck of a good looking truck and in fact that is exactly what these have always been to this day.

Cars that talk, have TV sets and bars, and use a wi-fi internet connection to find their way around and provide entertainment? And can be HACKED by someone with a laptop in a distant city to steer you off of the road?

Romel stated, "electronics will kill us" That is an understatement! We have some generation(s) taking over everything now who are crazy from the insane commercialization of every kind of mindless electronic gadget possible. Sorry to say, but these people are out of touch with reality and what is truly important in this world. They are now designing our future, in too many cases, toward inevitable catastrophe and the generations right behind them are eating this up like life is just one great big video game! Out of touch with reality? Even the Pentagon and military. Massive deaths and destruction by Joysticks and touch screens, oh what fun!! Wait until the special effects of Reality hit. It is not going to be a pleasant scene. Enough said on that.

Where was I? Oh yeah, fixing these trucks. Removing the bed makes it look SOOO EASY! That's obviously the way to go IF you have a place to do it. I don't. the tanks MUST come out for maintenance and repairs to senders etc. Maybe I will do it that way next year, especially if I decide to fully restore this truck as much as I possibly can. For now it is a passion and I want everything to work well and for it to look nice. If I get carried away this will be a showpiece! Once upon a time I was a very good artist and I have a paint scheme idea to start with that will capture some undivided attention at any show. I can accomplish the paint (if I so chose) but I know I won't have enough money to finish everything else out to custom show quality, like an expensive interior, etc. unless I find a giant gold nugget in the dirt next to a rest stop along a highway.

Really, I just want a good working truck that looks nice enough to be parked in a parking lot full of new trucks and one that is very well noticed as a nice truck.
Then I would have some equivalent respect (that I deserve and earned) while driving around town or out on the highway.

 

Late to the party, and I didn't read the whole thread, but the gauge pegging past full does NOT tell you anything about whether the sender is working. Pegging past full indicates infinite resistance, so it could be an open in the circuit anywhere between that sending unit and the selector valve. Could be either the ground or the signal wire from the sender to the selector valve. Not sure about your generation of truck, but on the next gen, there's a connector right at the frame rail, that goes to the rear tank sender. I would check the circuit there. Also check at the selector valve, of course.

 

Same here! Often, I chuckle when I think of my truck. It looks ok, but when I me thinks of the $700 a month I am saving for an equivalent truck, plus the $1500 property tax per year, I just smile. My truck isn't show quality or smooth as glass, but it is quite comfortable, rides nice, and the A/C is frigid. Plus, I get as high as 18.9 mpg on the highway. The only thing that concerns me, about my truck, is the low-back bench seats- much more dangerous than the high-back seats/buckets in an accident/rear-ender.

Good luck!

 

Thank you much for that excellent information. I hadn't considered the selector valve but have since looked up the troubleshooting processes which I will post as images from the manual but I didn't see one for 'gauge pegging at full' so your information is extremely helpful. The black ground wires from the senders go into the tail light wiring harness and also the ground point to the frame is the same as for the tail lights so should be easy to find near the tail light wiring.

Unrelated: While confirming my coolant temperature gauge wiring from the sender I found a mysterious tiny connector with small wires sticking out from the left side of the dash board. Looks like original wiring and I though it might go to the instrument cluster because it is small. I didn't find it in the manuals but it is probably there somewhere. I'll be posting the image to see if anyone recognizes it and where it might go before I take the the instrument panel out and possibly find that it doesn't go there. I'd appreciate it if you take a look at the photo but don't waste your time looking it up for me, I can find it eventually in manuals if it is there. Otherwise I'll dig through the dash wiring to find it.

Thanks again.

 

I am posting 4 images here for troubleshooting fuel tank senders/wiring, fuel (tank) selection valve/wiring - for the condition of no reading at fuel gauge. (Other gauge issues, like erratic needle might also apply)

There is another image for testing the tank selector switch on the dashboard. I will find that one and post it next. EDIT: I could not find it after a diligent but not complete search of the manuals, so I'll skip it for now.

Madpogue addressed the condition of fuel gauge pegged past full, a couple of posts above this one.

The credit for these images goes to Dave Graham Auto Literature Inc., for officially authorized and licensed (by FMC) scans of the 1987 Ford Shop Manuals for Light Truck, Bronco, F-Series Pickups, and E-Series Vans which I purchased at Amazon.com


Fuel Sender: Apparently the 1987 does not have the horizontal filter screen





Diagnosis Fuel Sender:






Tank Selector Valve - 6 Port:




Bypass Selector Valve TEST: