Fuel gauge issues - 73 240z

[GeoJoe]

Hi Guys... my 73 240z had a fuel gauge working fine. Last month it went intermittent on me, reading very low, then finally stopped. 

 

So I checked the fuel level sending unit and yes, it was leaking from the top connection. I figured this was also why I smelled gas when the tank was about half full. So I bought an OEM replacement sending unit and figured a 30min job to swap it out. I drained the fuel tank, got the old one out without dropping the tank and hooked the new one up. 

 

Two days later, dozens of searches and hundreds of pageviews and I still can't get the gauge to read anything. 

• I'm seeing the fuel sending unit reading a low fuel level with an Ohm meter, so that's good.
• I've tried to ground the positive for the gauge (near the fuel pump) to read full. No movement.
• I've checked the wire harness for the fuel pump and sending unit near the tail lights. It's intact.
• I've reached behind the fuel gauge to see if anything is loose... it all seems tight.
• I've checked the fuseable link to the starter and it's ugly, but working. 

Is there another fuse, ground or link that I'm not seeing?

 

All other gauges work (except clock)

Thanks all....

 

 

[SteveJ]

Joe,

Drive down to Tim McGovern's house this Saturday. I'm already going to look at his car and maybe Pat Carr's car. We might as well make it a full day.

[GeoJoe]

Thanks for the quick reply as always Steve. I'm on the track at Road Atlanta this weekend in the Audi. Maybe next weekend?

 

It's not urgent, but it's driving me crazy that I can't figure it out. Seems simple and I'm reading that these are usually cases of faults and grounds rather than bad gauges. 

 

I just replaced the glass fuses that control the gauges too... 

 

Can a fuseable link that is frayed have an affect on one part of the car, but leave other parts working fine? That's my next replacement.

 

Another possibility is that my recent paint job may have had an affect on the ground in the rear hatch. Where is this exactly?

Edited August 20, 2015 by GeoJoe

[siteunseen]

I was thinking if you put the two wires together it should peg on the empty side of the gauge? Could the clear lense be pushed up against the needle? Happened on one I bought, the guy kept finger tapping the actual gauge face trying to get it to work when the sending unit went bad.

[SteveJ]

Thanks for the quick reply as always Steve. I'm on the track at Road Atlanta this weekend in the Audi. Maybe next weekend?

 

It's not urgent, but it's driving me crazy that I can't figure it out. Seems simple and I'm reading that these are usually cases of faults and grounds rather than bad gauges. 

 

I just replaced the glass fuses that control the gauges too... 

 

Can a fuseable link that is frayed have an affect on one part of the car, but leave other parts working fine? That's my next replacement.

 

Another possibility is that my recent paint job may have had an affect on the ground in the rear hatch. Where is this exactly?

The weekend after that is over at Jai's place near Chatsworth. 

 

I'm betting on the electrical connection. A multimeter is your bestest friend.

 

If you're in town over Labor Day, you could bring the car over on Monday, and we can put it on the lift.

[GeoJoe]

I was thinking if you put the two wires together it should peg on the empty side of the gauge? Could the clear lense be pushed up against the needle? Happened on one I bought, the guy kept finger tapping the actual gauge face trying to get it to work when the sending unit went bad.

 

I've read the opposite. If you put the two wires that send the signal to the gauge together, it should top out at max fuel level. Doesn't work for me. For now it's just resting on the empty side.

 

Also to note, but prob not related - I have an intermittent tach that will all of sudden start working, them stop, then start again with a few taps on the lens.  

[240260280z]

I think the gauge is dead.  If so, don't try to burnish the bi-metal heater contacts inside as it will remove the special metal coating. Just try to bend them so that fresh metal touched fresh metal.

[beermanpete]

I second Blue's comment. The gauge is likely the propblem. Especially If the other gauges are working.

[SteveJ]

Here's the contrarian position. I had a fuel gauge that stopped registering. I got under the car and found the connections at the tank were loose. I got them tight against the sender, and I have a functioning gauge. I can test it with a meter and ensure there's a good connection, and I probably have a good fuel meter if it comes down to that.

[GeoJoe]

Well allright then.. thanks guys. Steve, I'll catch up with you soon and report back on what solved it.

[siteunseen]

So for my selfish benefit for right and wrong, what does the gauge do when the sending unit wires are joined together? Is that not zero resistance which shows EMPTY?

[gundee]

This just happened to my 72 two weeks ago.

It was just a blown fuse on mine. So far so good.

If it blows again then I have an issue.