Fuel Gauge and Sender

[sithot]

I've spent some time now attempting to trouble shoot a fuel gauge sending unit issue.

There's a thread I started on Pelican which lays it all out but since this is "home" I thought I'd lob it to the friendlies here.

I've tested resistance on the sending unit(s). I have 3. 1 is brand new, 1 is a year old and one is original to the car. They all check out.
Today I submerged a couple of them feeding the gauge through the body fuel sending unit harness. All raised the level but it quits at roughly 3/4 of a tank.

I'm voting gauge at this point as I also tested the gauge with a potentiometer and it did the same thing.
(Thanks to Lowes, McMaster-Carr and Amazon for the "home made" potentiometer parts) Anyone wanting a kit I have a spare pot, dial and can point you in the direction of the housing which needs to be modified a little.

I'd send it to NHS but in the spirit of impatience I'd also like to find a REALLY NICE used one.

Part number is: 911 641 202 29

Thanks,

Tom

[Florio]

Hi, I recently opened up my temperature gage because I was worried it was faulty and because I was curious. The system is made up of a wheatstone bridge with a resistance on the positive terminal to limit the overall current in case of a failure. The values of the other resistances in the bridge determine the full throw of the gage. Normally, the resistance will go down to move the gage up (to full or high temp or high pressures). So, I would guess you have an "extra" resistance in series somewhere. It could be a dirty contact (as it was in my case), or maybe a failed component or cracked solder joint. I would start by **really** cleaning well the wire contacts. Mine were clean, but not good enough (sandpaper needed). Then, the fuel gage component comes out the back of the gage. If you're up for this, post pictures and we'll try to help!

good luck,

[sithot]

Hi, I recently opened up my temperature gage because I was worried it was faulty and because I was curious. The system is made up of a wheatstone bridge with a resistance on the positive terminal to limit the overall current in case of a failure. The values of the other resistances in the bridge determine the full throw of the gage. Normally, the resistance will go down to move the gage up (to full or high temp or high pressures). So, I would guess you have an "extra" resistance in series somewhere. It could be a dirty contact (as it was in my case), or maybe a failed component or cracked solder joint. I would start by **really** cleaning well the wire contacts. Mine were clean, but not good enough (sandpaper needed). Then, the fuel gage component comes out the back of the gage. If you're up for this, post pictures and we'll try to help!

good luck,

I will take your advice and do this.

Thanks!

Tom

[sithot]

While checking the actual fuel instrument movement out of the case with the sender working (power on) I touched the needle while it was registering at the top of its range which was somewhere around 3/4 full. It was easily manipulated to the 4/4 full mark which I figured isn't the way things are supposed to work.

Going to the trunk I placed the sending unit upside down. The gauge went to empty and the reserve light turned on. I rotated the sending unit 180º a few times observing the movement. The needle swept from top to bottom and vice-versa. The range was now 4/4 (full) to Reserve (light on). I considered calling it "fixed" but then again if it was this easy, why hadn't someone else done it?

I put the gauge back together and sent it to North Hollywood Speedometer along with my clock which had been correct twice a day for a long time and now two issues will be taken care of.

On a brighter note, I ended up with my own “custom” Potentiometer and a gaggle of wires made up to test the sending unit, harness and of course, the gauge!

In closing, NHS said the gauge is "hanging". The clock will cost more which I knew but it did give pause to consider a block off plate.

Will update when the parts return.

[ejboyd5]

Probably more important to have accurate readings when nearing "empty." Forget about the upper range.

[sithot]

Probably more important to have accurate readings when nearing "empty." Forget about the upper range.

I agree 100% and why I left it to "the professionals".

[sithot]

The gauge went to North Hollywood along with the clock which hummed but didn't keep time.
Received them after within a week (expedited shipping). The clock is now keeping time.
According to the guys at NHS, the fuel gauge was "hanging".

Gauge in the car is sitting on empty, reserve light on. I'll attach a sending unit to determine full range of motion and may or may not leave the car empty until it's brought out again. Winter is here and good days to drive will become scarce.

Thanks to all for the advice.