Fuel gauge not working - goes from 1/2 way to 3 o'clock

[THEMCGUIRE]

Back in 2009 I bought a new fuel sending unit and installed it. The car sat for years until a few months ago when I finished my rebuild. When attempting to get it running I found that the pump failed, I guess from lack of use. I had to take the sender out of the truck a number of times till I got this fixed. During one of those times I caused the fuel level sender wire to become disconnected.

I believe I found where it belongs and soldered it back in. But since then the gauge is pinned at 3 o'clock.

Today, looking to fix it, I removed the sender from the tank. Attached voltmeter to the ground on the sending unit and to blue wire where I soldered it back in place at the gauge. Moved the float arm up and down and ohms changed from 33 at low to 105 at high.

Inside the sending unit there is a blue wire going from the gauge to the connector at the top. This becomes a purple wire when it exits the sending unit.

The purple wire connects to a the tan wire near the rear driver side tire, that runs to the engine bay (I don't know why it changes color).

I tested the tan wire at the junction box in the engine bay to the blue wire at the float, I have continuity there. So this confirms that the wire to the engine bay is good... I did not think to test the ohms at the tan wire in the engine bay while I had the sender out of the tank. Duh...

With the fuel gauge removed from the instrument cluster, I tested voltage from the left hand connector to the bottom connector (ground) I get 12 volts.

When I test the tan wire in the engine bay to the right hand side connector that the fuel gauge plugs into I get no connection.


I think this means that somewhere between the engine bay and the gauge connection there is a break? I find this odd because the gauge was working fine when I installed this new fuel pump assembly and before I broke off the blue wire in the tank.

When I use a jumper from the tan wire in the engine bay directly to the gauge and then connect the other 2 connections on the gauge it still does not work correctly.

Does this confirm that my sender is working correctly ?

What else should I check before buying a new, expensive, sending unit ?

 

[dyeager535]

Easiest way to test the gauge and all wiring before the framerail connector near the tire:

Disconnect the plug, watch gauge with key in run. Should peg out one direction. Now ground the tan wire in the connector (I'm assuming you've got that all right, and the tan is the sending unit gauge wire, it sounds right) and the gauge should peg out the other direction. Might take a few seconds, but it has to if working right.

If the gauge doesn't peg out in both directions as it should, there is a problem with the wiring FORWARD of the tank. If so, I'd suspect the instrument panel connector. But start with figuring out if the gauge works correctly first.

 

[THEMCGUIRE]

Oh I already did that. I grounded the tan wire to a bolt in the engine bay before removing the gauge from the instrument cluster.

When I touch the tan to ground the gauge went to empty. Slowly but it went. When I removed it from ground it went back to 3 o'clock...

 

[dyeager535]

So definitely either that connector by the wheel, or anything from that connector back, including the actual sending unit.

Tank ground I would check (just see if the tank is grounded at all). Since ground=full empty, and makes the gauge work, the tan wire isn't shorted to ground it's open, so I would suspect an issue with the tank ground itself.

 

[THEMCGUIRE]

Fixed

I ran a new line from the fuel sending unit directly to the connection behind the cluster... 1 inch from the printed circuit.

It works.

I did this because this line between the gauge and sending unit is a non fused line. That made me think it was ok.

3 fffing days on this wow.

Thanks for the help.

FYI Here is where I repaired the sprain gauge. Follow the blue wire. Saved a bunch of money repairing instead of replacing.

 

[herkdriver007]

I need to do some troubleshooting on mine...
Full is around 3 o'clock...empty around half on the gauge

 

[THEMCGUIRE]

So it works but just off, sounds like 90 degrees give or take.

Have you inspected the sending unit ?

That would be my 1st step.

How old it the sending unit.

 

[herkdriver007]

Yeah it sweeps both ways... Dropped the tank last yr for my shackle flip but should have inspected the sender then...
Best I can tell, oem.

 

[THEMCGUIRE]

i changed the name of the post so it would reflect your issue.

From what I have read if it works at all it is NOT the wiring.


So it must be the sender.

Photo shows the hole in the deck I made to access my tank. Got tired of dropping it. To close it I just seal all around with silicone. Underneath I used old rubber molding to hold it up and help seal it.

I would pull it again and check it out. Most likely the sending unit. But don't take my word for it.

 

[herkdriver007]

Thanks for the help!
Yeah, I should pull it to further my TS... Just found it interesting it would sweep fully and look normal, until hooked up to the sender with a full tank...then off to 3 we go