Fuel Gauge on E, low fuel light on -unknown problem

Ripster · **Posted:** Sat Oct 17, 2009 4:31 pm

I have been troubleshooting my fuel gauge for the last several weeks. First off I have the cumming lift pump mod in the tank.
I took considerable care in the wiring and when it first happened the guage made a ding sound and the needle went to E.
For the next few weeks it would come on and off depending on road or tilt, or it could have been anything. So I replaced
the module in the tank, still no work. So now that I have a new lift pump, I decided to check the ground under the seat, no
problem there, I even went and redid the connections on the splice going to the tank or the extensions that I put in
with the 05 harness. Fuel gauge is pegged on E with the low fuel light on. Any ideas? I would suspect the gauge last
but who knows. Sometimes it would work for several miles and then just die. Now it has stayed on E for the last
several days. Fuel pump works fine.

Joe Romas · **Posted:** Sat Oct 17, 2009 5:12 pm

If you can reach the plug on top of the tank remove it and connect your original level sensor and see how it operates. I don't remember if you can reach the plug or not with the tank in place. When you put in the Cummins pump module did you cut the tab so it would fit exactly where the original was?

Ripster · **Posted:** Sat Oct 17, 2009 7:12 pm

I do not have the original, the tank pump is not the issue, I tested the one I took out and the one I put
in and they both test and work as you raise the level, the resistance changes. And you can not reach
the top without dropping the tank, and whether you cut the tab or not, does not matter except when it
gets low, as it will be empty around 1/4 tank, I have put enough fuel in the tank now that it should register.
I am assuming that the gauge would be the last thing to go, and that the wiring bringing the fuel level to
the gauge is the problem, but I am stumped. The first lift pump I did not cut the tab, the second one
I did a bit, so that my fuel level would be more on target.

warp2diesel · **Posted:** Sat Oct 17, 2009 8:04 pm

See if you have a signal going to the sending unit. Chances are that it will be 12 volts or less, or it may be a pulsing hand shaking type signal if it is on a bus where it is coming out of the body control module. I would lift up the rear seat and check at the plug under the seat. To isolate the voltage going to ground from the fuel pump, I would pull the fuel pump relay fuse. Another trick would be to make a logic probe with an LED and 1K resistor. The long leg is the Anode (Andy, an easy way to remember) and the shorter leg is the Cathode (Cathy), ground out the Cathode and touch the Anode of the LED/Resistor to the pin going to the sending unit.
Then remove the ground fuel pump/sending unit ground and see if you have the signal coming out and through the sending unit.
Another trick would be to unplug the body module and measure the resistance between 17 C2 and 15 C2. If you have an open circuit, you have a continuity problem some where, most likely in a connector pin at one of the plugs.
Here is a page out of the 2006 FSM.

Ripster · **Posted:** Sat Oct 17, 2009 8:41 pm

warp so you are figuring that one of the pins in one of the plugs from under the seat going back
to the tank could be my problem. If we are playing odds, the odds would be the connections
added to install the lift pump. When I put a tester on the lift pump, I could see the resistance
as I lifted the float. So my question is this, if I connect across the two prongs coming from
the tank back at the plug under the seat, wouldn't I see that same resistance there also
on the way to the gauge?

warp2diesel · **Posted:** Sat Oct 17, 2009 9:54 pm

Ripster wrote:

warp so you are figuring that one of the pins in one of the plugs from under the seat going back
to the tank could be my problem. If we are playing odds, the odds would be the connections
added to install the lift pump. When I put a tester on the lift pump, I could see the resistance
as I lifted the float. So my question is this, if I connect across the two prongs coming from
the tank back at the plug under the seat, wouldn't I see that same resistance there also
on the way to the gauge?

Yes and you should get the same resistance at the Body Control Module plug too.
When I was in the repair business, I fixed a lot of lousy connections at plug pins. The only place I found bad wires (unless they were fried) were where they flexed a lot, like Drive side doors and firewall to engine wires.
Now most of the bad connections are where the Electricians hook the field wiring to control panels, racked up a bunch of free Airlines trips.

Good Luck

Ripster · **Posted:** Sun Oct 18, 2009 4:53 pm

Pulled the complete wiring from the plug under the seat to the tank and sure enough there was one
of the sender wires with no resistance. Found a connection that was oxidized in the connector.
With the 05 you had to extend the wires, even with crimp and soldered connections one had the
green oxidation which caused the issue. My question to those who have done the lift pump, with
the 06 wiring harness work on the 05 without any spliced connections, so that I can be done
with oxidation of the current connections over the next few years. This one almost made 2 years
but crawling under that beast is not fun. Anyone use the 06 with out splicing on the 05 system.
thanks

warp2diesel · **Posted:** Sun Oct 18, 2009 7:15 pm

Pack it full of the paste you would use on a trailer connection plug.
Wash off any rosin from soldering and keep the salt or alkali dust out, then your plug won't go green.
In waste water we have to put up with H2S and Ammonia, even with 120 volts, it corrodes the connections, keep the gas out and the problem goes away.

Fuel Gauge on E, low fuel light on -unknown problem

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