Where exactly is the gas tank ground on a 81 FB? Chasing a fuel gauge that often sits at empty, and always reads lower than actual. Did some research and before removing and testing sender I am checking ground. Posts mention checking fuel tank ground, but can’t find a strap or wire. Do see a broken wire near rearmost exhaust mount, which I will fix, but nothing else.

 

That's the only one that I'm aware of, that's a shot of mine, an 83.

 

Thanks. Have reconnected that one now. Looks like I have multiple causes. Pulled the fuel level sender (thanking CA for being dry… no rusty screws) and no resistance reading across connector blades. Cleaned everything up and now getting the correct readings at full, half and empty. Reinstalled, but gas still reading empty although getting 76 ohms at sender connector blades. Maybe bad gauge? Good thing I am retired and do this for my own entertainment.

 

This thread has a lot of good information...

https://www.rx7club.com/1st-generati...-good-1106492/

You'll get this sorted!

 

Excellent thread. Sounds like my kinda guy!

 

I had an issue like this and the solution in my case was to add a small ground wire on the sender from its center mount to one of the bolts that holds the sender in. The problem is with age the sender is not grounding to the mounting plate as it should. I don't have a pic of it. Let me see if I can get one.

 

Is the bit you ground this copper piece here?

 

Kind of, you see that small square of metal below the plastic? That is what looses its connection the round base plate that gets bolted to the tank. I just tapped a small hole and put a screw into that plastic mount that hits the metal below and ran a wire out to one of the screws holding the base plate to the tank. You can verify this by reinstalling the sender and jumping with probes from that square metal to one of the screws to see how it works. Just remember that the change in the level gauge is not instantaneous, give it a good minute or two to react.

 

[QUOTE=t_g_farrell;12626784]Kind of, you see that small square of metal below the plastic? That is what looses its connection the round base plate that gets bolted to the tank. I just tapped a small hole and put a screw into that plastic mount that hits the metal below and ran a wire out to one of the screws holding the base plate to the tank. You can verify this by reinstalling the sender and jumping with probes from that square metal to one of the screws to see how it works. Just remember that the change in the level gauge is not instantaneous, give it a good minute or two to react.[/QUOTE

Aha! Raining the next few days, but once it is dry again will give it a go. Thanks.

 

Well that took me longer to get to than I estimated.

Tried grounding the metal plate you described. No difference. Tried grounding other bits of the connector, but no difference also. Verified the screw I connected to does ground, and tried grounding to the ground strap to the tank also… no change.

Will dig into how the gauge wires to the sender and work my way upstream.

 

There is a connector for the fuel level and low fuel in the drivers side wheel well behind the plastic. You can take some resistors or a pot and attach it to the fuel gauge side of the connector to validate the gauge.

https://grannys.tripod.com/rx7info.h...2075.9%20ohms.
Fuel level sending unit- full=6 ohms / 1/2=31.5 ohms / empty=80 ohms.
Fuel level gauge- full= 7.4 ohms / 1/2=31.5 ohms / empty= 75.9 ohms.

 

Excellent idea. Found a variable resistor box on Amazon. If it turns out to be gauge I may just have to leave it be. I have a glued on dash cover and I think the lip around the gauge cluster is going to make things difficult!

 

Ok… got me a variable resistance box. Where exactly am I looking for a connection. Wiring diagram shows one behind the drivers seat and one waaaaaaaay under the dash.

 

X-03 would be the easiest. One side to X-03 Yellow with one side of the resistor and the other to a ground or body metal. I haven't done this myself but need to. I think my tank level sender is off.

 

Would that be any different to applying resistance at the connector that attaches to the sender? I already have that exposed, so attached my resistance box to the two female ends of the unplugged connector. For the gauge to read empty it took 90 ohms bottom of red and 70 ohms top of red. 1/2 full took 20 ohms. Was unable to get the gauge to read full, at 0 ohms gauge read 3/4 full.

Looks to me like the gauge is the issue. Second f opinion?

 

Based on your troubleshooting, I would suspect the gauge at this point. I'd send you one but mine are all 1984/1985.

 

The gauge never going above 3/4 was the exact behavior I had in my 83 and in the thread I referenced. I fixed it by calibrating the gauge with the adjustments back in that thread.

Good luck!