dual fuel tank gage
 

I have a 86 E350 cutaway with dual tank and the front gage is reading Empty regardless of the fuel level in the tank.

I'm looking to troubleshoot the problem but the wiring colors in the Haynes are not the same as on the truck.

I found another diagram and the colors aren't the same too.

I would like to test my wiring before dropping the tank and can't find the right colors to test the fuel sender.

The wiring from the front tank has a green, brown and couple of black wires.
Also the fuel selenoid valve has 5 wires (red, green, green, brown, orange)
I can't find these colors on any diagrams.

Thanks for your help.

Check the float in the tank. I bet it's split. Or defective sending unit.


Haynes manuals are generic, and are a compilation of several different diagrams. So they are not complete, and have some acuracy issues. Autozone has some good diagrams but they are also generic, and incomplete. Only showing idiot light main harness diagrams for example.


Your best bet is to get a Ford Diagram for the specific vehicle you are working on.

Since you have a cutaway, the wiring may be different because the company that bought the incomplete vehicle from Ford may have wired it their own way as well.

You may get better help in the VAN forum as well too.

Good luck.

No "front gauge".
The gauge serves both tanks.

It is mostly always the FRONT tank sending unit.

Have you done the wiring tests yet for a broken circuit (a wire for example) ?

The system works on a pulsing signal of 5 volts in assoctaion with a grounding out of the sending unit.

If the system get ground with power pulsing the gauge pins.

If the system doen't have a pulsing voltage whether the sending unit is grounded or not the fuel gauge needle will not move from empty.

I would go with taking out the sender, checking the float, if it is ok, then check the resistor on the sender, but my money would be on the float being filled with fuel or such, but the resistors also fail.

I would go with the "drive by odometer method", cheaper, trouble-free.

That's what I'm doing for now. Drive on the front tank until engine begins to stall then switch to rear tank with the gage that works.

By the way, I just want to make some electrical tests before dropping the tank to check the float. My problem is the wire's color that don't match both chilton or hayes!

Thank you

Fuel Gages operate the same way as an ohm meter and measure resistance to ground, but only within a calibrated range and direction. Power & ground is supplied to the gauge to power the meter. A signal is produced on the “S” terminal, which is then connected to the fuel tank sending unit. The fuel tank sender then receives that signal and varies resistance to ground. The sender can be thought of as nothing
more than a variable resistor. This is why the sender also needs to have a 2nd wire going to a common chassis ground, otherwise the sender would not have the ability to
vary the resistance to ground. If you use a multimeter and disconnect the battery you can do the tests below.

If the gauge increases in resistance from Empty to Full, such as 0 to 90, 0 to 30, or 15 to 160, and assuming that the gauge is properly matched to the sender then the most common cause of this type of gauge to read over full is typically due to no ground at the sender, an open circuit, or a break in the wire going from the gage to the sender. A easy way to check the gage is to remove the sender wire off of the back of the gauge, leave the power and ground hooked up and use a jumper wire to connect the “S” terminal of the gauge to ground. Turn the power on. If the gage responds by going to E, then you have proven that the gauge responds well. Jumping the “S” terminal to ground is the same as 0 ohms of resistance to ground. Having no wire or jumper on the “S” terminal is infinite resistance to ground which is much greater than the gauges F reading which then will cause the gage to read past full. If when you jumpered the “S” terminal to ground and the gauge did not respond by going
to E, you will then check power, check ground, then check the ground you jumpered to. Now you know if its the gage or the sender is at fault.

He mentioned in the first post the problem is the FRONT tank.

I'm sure he would have mentioned both tanks not reading on the gauge.

Therefore IMO, the Gauge is okay and either the SU or the wiring for ONLY the Front tank is the problem.

My guess: Bad ground connection of SU or faulty SU.

Here's what I reply to another post.

"
I ran my tests yesterday and the results with the connector at the selenoid unplugged were:

rear tank - full - sender reads about 18 ohms.
front tank - empty - sender reads about 70 ohms

I also received at the plug, the pulsed 5V.

I went to the gas station and fill the front tank and took another reading on the front sender. That time it reads open circuit. The gage is still marking empty. The sending unit should have read about 20 ohms.

I'm now almost certain that the problem is on or in the tank. I will have to drop it.
"

Locknkey very well explained the theory of operation of fuel gauge. In this case, resistor values are the opposite way of what you explained, but the operation is the same.

Then, with an aligator clip I grounded the sender wire and the gauge went to F position. With the aligator Open, gauge read E.

You can get the sender out of the front tank without having to drop it, done that a few times with my 250.

Boy! I have a motorhome and the tank is up to the floor. I can't even put a hand over it.

I know that the sender is right on top near the side but absolutely no room to work.

If you have a trick that I don't know, let me know!

Here's the schematic you may have wanted earlier from one of many pages on my site.

I hope the information I provide is helpful to you :)

http://www.clubfte.com/users/mil1ion...strations.html

well, I imagine they make the motor homes a bit different. If you can get most of the fuel out, it makes the job go easier. It isn't all that hard to drop the tanks usually, just goes a lot easier to have the fuel out.

I'm glad to see this thread. In my case, the rear tank never works and the front works intermittently. I'm guessing that both sending units are bad. That's a total guess by the way, but the fact that the one does sometimes work indicates to me that it's probably a tank issue. If you think differently, I'm listening!

I was using the dead reckoning method...except that I now have a working generator that runs off the front tank. :) No longer is it simply miles I have to worry about; I also have to figure in how much time the generator has been running. That makes it a lot harder to estimate how much fuel I have left. :)

(Honestly, it'd be better probably to install a second fuel gauge for the one tank and have the other always show on the dash. I'm not sure I have the time and energy for that right now, though, and that still requires the sending units to be working.)

My question is a bit dumber, though - where can I get new sending units? Is the Ford dealer the best place?

Thanks.
--RJ

Just click the BOTP logo at the top of the first post listed in this thread.

EDIT:
Never mind I found it.

http://blueovaltruckparts.com/catalo...p?cPath=99_102


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