Fuel gage/sender problem - how to test?

[Kerrigan]

My fuel gauge stopped working after the car sat for a month with a full tank of fuel.

I need to test to find out if the tank sending unit is bad or the gauge itself.

I can't make heads or tails out of the testing procedure offered in "that" UK printed manual.

Does someone know how I can test the tank unit easily?

Thank you!

Kerrigan

[zbane]

Potentially stupid questions here:

Have you checked that all of your electrical connections are clean and solid, from the sender to the instrument cluster?

How clean are the float contact points on the sender itself?

[Nissanman]

Refer to the thumbnail attached:

The gauge terminal of the tank transmitter can be temporarily connected to earth and that should force the gauge to read maximum scale, if everything else is working OK.

As mentioned, there are a fuseable link and a fuse to be checked in the Fuel Gauge circuit.

There is also a Voltage Regulator, shown at the LHS of the gauge, which controls the voltage applied to the gauge.

These have been known to misbehave and cause erratic readings usually on the Fuel and Temperature gauges.

Cleaning the contacts on the VR and all points in the diagram may remedy the problem.

[Curtis240Z]

An emtpy tank sender would read 90 ohms, a full tank 10 ohms. Nissanman is correct in diagnosing the wiring system, just ground the wire and it should read full scale.

[JSM]

Old thread yes I know. 71 240z, So my gauge doesn't work. I was able to get it to full sweep by connecting the yellow wire to the black wire which tells me my sending unit is bad.  Just to be clear the yellow wire on the tank goes to the top of the Sending unit, bottom is ground correct?

The new gauge I'm using is from my old 73. (My current one is falling apart). VisuallY the wires match up at the plug, however, I'm getting a very faint amount of some coming from the gauge that last for a second. Dust, dirt in the gauge? Do I leave it pegged at full and see if it (gauge) heats up and or pops the fuse?

Also my car has the GM 90amp upgrade. Maybe I should try with it off vs running to see if the amps are causing smoke?

Edited August 27, 2017 by JSM

[siteunseen]

The glass was touching the needle on mine causing it to stick in certain spots. The SU went bad and the PO tapped the lens so hard it came loose.

I used liquid electrical tape on the nail head connectors on the SU. Those things are a one time every 40 years deal, to get them off I destroyed mine.

I have the P/N for a 240 SU from Nissan. My local dealership charged me $43 I think and $1 for the o-ring. If you want it let me know and I'll get it out of the file for that car. Cliff

[siteunseen]

Here's the thread with the new sending unit and a photo of the black and yellow on MY car. I'm thinking the connectors on the SU were different sizes to keep the polarity right.

http://www.classiczcars.com/topic/49439-developing-story/

[JSM]

3 hours ago, siteunseen said:

The glass was touching the needle on mine causing it to stick in certain spots. The SU went bad and the PO tapped the lens so hard it came loose.

I used liquid electrical tape on the nail head connectors on the SU. Those things are a one time every 40 years deal, to get them off I destroyed mine.

I have the P/N for a 240 SU from Nissan. My local dealership charged me $43 I think and $1 for the o-ring. If you want it let me know and I'll get it out of the file for that car. Cliff

Thanks. Yeah my wires were completely off when I got the car back. 

On your other thread I noticed a 90 on one of your vent lines above the tank was that to prevent kinking? 

Edited August 27, 2017 by JSM

[JSM]

Well I tried it with the car off and it was just a fine vapor barely  noticeable and it stopped altogether. I started it and ran it for about 10 min and no smoke. Gauge was only Luke warm. Not sure if this is normal or not. Disconnected the two tank wires and gauge dropped as it should. 

Edited August 27, 2017 by JSM

[JSM]

SU, O-ring and lock ring $72.02 shipped from courtesy. Prices have gone up. 

Always weird to me what is NLA. I figured I wood get a new plug and tank washer, nope. 

[siteunseen]

2 hours ago, JSM said:

Thanks. Yeah my wires were completely off when I got the car back. 

On your other thread I noticed a 90 on one of your vent lines above the tank was that to prevent kinking? 

Yes. There was a pre formed hose right there. I used a 1/2" PEX ninety there. Used two 3/4" PEX 90s to make the big bend on top, 5/8" hose. 

[siteunseen]

1 hour ago, JSM said:

SU, O-ring and lock ring $72.02 shipped from courtesy. Prices have gone up. 

Always weird to me what is NLA. I figured I wood get a new plug and tank washer, nope. 

I still get parts for my SUs from the dealership. They made as many, if not more, forklifts that use a bunch of the same 2.4 components. 

Edited, L20s in the fork lifts I'd imagine but still motor parts. I bought a new pair of door scuff plates a month ago. Better than the OE ones and $20 per side. Nothing else uses those so they're still in the parts business money making side.  Smart guys. Genuine Nissan ain't repop on ebay.

Edited August 27, 2017 by siteunseen