by TTait » Tue Jun 22, 2021 5:49 am
I wonder if it actually the vibration, or if the signal is being corrupted electrically.
The float is on the end of an arm so even if the car had bad motor mounts causing the gas to be stirred around in the tank the float would barely notice the ripple.
I'd inspect the wiring for breaks to see if the vibration is causing an intermittent short to ground. The wires come off the top of the tank and then up into the trunk/hatch area inside the car. Look for damage to the wiring in this area first, particularly damage to the tan wire.
You should find a connector you can get to inside the trunk/hatch area. Assuming you are still running an in-tank fuel pump you need to leave it connected to run the car, but you can probably get a meter onto the tan and black connections with it still hooked up, If you no longer have an in tank pump you can disconnect it during diagnostics.
Hook up the meter and read the ohms value between black and tan. 90 ohms is a full tank, 0 ohms is empty. your reading shouldn't fluctuate much whether the car is off or on.
If it is fluctuating, turn the car off and disconnect the connector and read off the tank side of the connector only, if it is still fluctuating then the problem is with the sender or the wiring to the sender. If it was jumping around when connected but is steady when disconnected, the the problem is somewhere the wiring up to and including the gauge.
You can also pull off the instrument cluster bezel and lens and then the two screws holding the fuel gauge in place, pull it our a few inches and unplug the gauge from the harness and read the resistance from black to tan, or from black to the non-pink wire as the color may have changed by the time it gets to your gauge. Is it stable, or jumping? Does that change when the gauge is plugged in?
Next check the DC voltage at the gauge from pink to black. It will be 0 with the car off and 12.75 to 14.5 volts when the car is running. If that fluctuates quickly more than about a quarter of a volt then you may have Bad power or ground. If you saw fluctuations on any of the ohms reading before and also on the DC voltage at the gauge its likely the ground. Check this by keeping the red lead from you meter hooked up to pink and move the black lead to a good ground point on the body of the car, maybe the metal sill plate in the door or the parking brake or similar chassis ground point. If voltage is now steady then you have a bad ground. Read the ohms again with one lead on the tan (third color) wire and the other lead on your chassis ground and see if it is now stable.
If you are able to isolate the problem to a noisy ohms reading coming from the sender itself - best measured from the unplugged connector at the rear of the car - then your going to have to drop the tank and repair/rebuild/replace the sender.
That is doable - but there is more to discuss if you really have to do that.
Probably lots of typos - its late.
On my third H Body - 1975 Monza 2+2 4.3L Orange/Black (Current State: Running great - needs the AC finished before summer hits hard)
76 Monza 2+2 L4 (1982-1987)
77 Starfire V6 (1987-1987)
82 Delorean - Universal Raffle Car (2005-2013)
81 Delorean 2009 - Present
17 Chevy Bolt 2017- Sold back to GM for almost a full refund
22 Mustang Mach E on order