Technical Fuel gauge problems

Here’s my question for this weekend (buckle up, a lot more coming this year):

Fuel gauge on the 48 is reading erratically/inaccurately/useless. It all appears to be after market stuff, nothing stock. Aluminum handmade tank, unknown sending unit, and some kind of cheapo aftermarket gauge. I know you’re gonna start out by saying “not enough info to help”, which is fair, but that’s my question. What do I need to find out in order to begin making my fuel gauge read properly?

The gauge activates when I turn the key on, but just warbles around aimlessly. Never shows more than half full, but also doesn’t properly show empty. It actually doesn’t seem very concerned at all with how much fuel is or isn’t in my tank. Will slowly move a quarter sweep in 5 minutes of running the car. Any tips for where to begin?


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Are the gauge and sending unit matched ?

Some sending units go from high to low resistance and others low to high and you need the appropriate gauge.

Is it wired correctly ?
Good grounds?
Goodconnections?

Is the tank bafelled or can the fuel slosh around?

Disconnect the gauge from the sending unit and it should either peg at E or F depending on its internal resistance

Can you get to the sending unit easily?
If you can yank it out if the tank and do a resistance check going full sweep and the resistance should change all the way through it’s travel smoothly

 

Number one: check all the wiring connections for corrosion and tightness. (might take an hour)

Number two: check all wires for fraying and shorts. (might take three hours to check all the length of the wire)

 

Remove the gauge and the sending unit from the car and get it on the bench. Hook it up using a battery and move the float and watch the gauge. Should be easy to figure out what the problem is on the bench. If both are cheap aftermarket crap you may need to replace both with a matched set from the same manufacturer.

 

BJR has good answer, have had similar problems. There are OHN differences with senders and need meter that matches. Don't buy cheap stuff.