Tom69

I’ve been troubleshooting my fuel quantity system using the guidance from Willcox Corvette’s website.

Problem: The gauge never reads below 2/3 full. When I top off the tank, the gauge reads beyond the full level almost to the 2 o’clock position.

Trouble shooting per Willcox directive:

• Voltage to gauge and sender is good.
• Disconnecting ohm’s wire: Gauge reads at 3-4 o’clock position. Checks good.
• Grounding ohm’s wire to frame: Gauge reading stopped at ½ tank. The reading was supposed to go to “empty”.
• Checking sender continuity. Checks good.
• Checking ground wire to frame continuity. Checks good.
• Checking sender resistance (tank was almost full): Read 85 ohms, a full tank should read 90 ohms.

I tried to hook the sender float arm with a grounded wire but for the life of me I couldn’t hook the float to move it down to see if the fuel gauge reacted to it. I plan to drive the car to nearly empty then re-measure the sender resistance to confirm the float arm is not sticking at an intermediate position.

I’m thinking I might have a faulty sender or perhaps the resistor at the fuel gauge is faulty or weak.

I sent an inquiry to Willcox but have not heard back yet. I would appreciate your best guestimate.

Thanks,
Tom

Tom69

Received the Willcox Support feedback...they are no longer answering questions pertaining to fuel gauges or wiper motor questions. They give links to those troubleshooting procedures, which I used.

This weekend I will drive down the fuel tank quantity to check the sender float range of operation and resistance. Looking at the internal wiring diagram of the fuel gauge, it appears to have two internal 160 ohm bridge circuits. The fact that the gauge never reads below 2/3 full, I bet one of the bridge circuits is open.

Tom69

Apparently just talking to myself on this thread...but maybe my troubleshooting will help someone else.
Since my fuel quantity gauge did fail one of the continuity tests, I still wanted to check if the float sender was operating full range or stuck in an intermediate position. I started this process with almost a full tank of gas, so yesterday I participated in a club sponsored road rally and managed to lower the fuel quantity to 1/2 tank. At that fuel level, I was able to see the float and manually move the arm to the tank empty position while watching if the fuel level at the gauge was responding. The gauge would not indicate lower than 1/4 full, so since the gauge previously failed one of the continuity tests, I still needed to confirm the fuel sender float was not sticking at an intermediate position. I had no convenient way of draining the tank so I took the C-3 on a 110 drive today to near empty tank. The float was resting at its lower limit of travel (float arm not sticking) and the float resistance measured "zero" which is the proper reading at low fuel indicating the float sender is working okay.

So today I pulled the fuel gauge and ordered a new one from Willcox. Also decided to paint the bezel. Hopefully the fuel quantity issue will be resolved.

Tom69

I’ve been impatiently waiting for my new fuel gauge to arrive from Willcox. Since I had some down time I repainted the center instrument cluster bezel and the wiper panel module. I repainted the letters using a cosmetic “single-ended applicator” which my wife picked up for me at CVS. The applicator worked great.

With respect to my faulty fuel quantity indication problem, I’ve had an epiphany of sorts…the fuel gauge that I removed looks relatively new. It has the 90-ohm wound resistor mounted on the back. I’ve been told that the new fuel gauges no longer require that resistor.

If so, that possibly explains my indication problem, just remove the resistor from the existing gauge. Since the new part is inbound, I’m hoping there are some installation instructions confirming that fact.

Any input from you would be appreciated.

Tom69

TaDA!!! Installed new fuel gauge from Willcox and fuel quantity indicating problem is now fixed.

The new fuel gauges do NOT require the external 90 ohm resistor.

Hopefully me stumbling through this troubleshooting process will help someone else.

Regards,
Tom

7T1vette

Perhaps the gauge you replaced was ALSO a replacement gauge...but the owner at the time reinstalled the 90 ohm resistor THAT WASN'T NEEDED. Your gauge may be fine but should not have the resistor installed with it.

I would hold on to that gauge....just in case....

Tom69

Yes, I made that same assumption. I was tempted to just remove the resistor and install the old gauge but decided to wait until I received the new gauge. I didn't want to chance doing any electrical damage to the circuits with the old gauge so just dumped the old gauge and resistor into my parts saved bin.

The instructions that came with the new gauge stated that this gauge is much more accurate. I'm glad with the upgrade. Btw, you use all the external parts of the old gauge minus the resistor when mounting the new.

Regards,
Tom