This has bugged me for a while.
'86 Town car with electronic 'bar graph' Fuel Gauge.
More often than not - the reading is wrong for the 1st few mins. Usually a LOT lower than it should be - eg showing empty when tank is full. If I drive long enough (20 mins?) - it usually climbs and settles to the correct value.
If the engine is off, and I turn the key to ON, wait for Display is finished its power on sequence, then OFF
- gauge comes back to a different point each time.
And this is very common:
- Car off for a length of time
- Start and drive off. Fuel level is usually correct.
- Stop car for 5 mins at shops
- Restart car. Fuel Display = ZERO (!) for about 5 mins.
Diagnostics
1) This gauge is designed to flash 3 symbols if the circuit to the fuel sender is open circuit. It NEVER does that - unless I disconnect the rubber booted connector on the fuel tank.
2) Measure 12VDC on the 2 connectors inside that boot with ignition = ON. (Manual says 10V or more is fine)
3) Measure exactly the correct resistances with a multimeter connected to the two connectors on the fuel tank. eg: Empty fuel = about 10 ohms, and full tank = 190 ohms (This matches the manual values). While measuring - rock car up/down. Values stay steady (+/1 one or 2 ohms). No sudden jumps to high or low resistances (as I would expect with a worn variable resistor in the tank).
4) The way this is designed, higher resistance = More Fuel. So ... if I had a corroded (ie resistive) connector for example, I assume that the gauge would show MORE fuel than I have...but it shows less most of the time.
5) Connect a fixed resistor of about 100 ohms to the 2 connectors in the rubber boot. Ignition = ON/OFF. Fuel Gauge displays different values each time.
Conclusion:
- I think the sender in the fuel tank is OK and not giving bad readings.
- I think the circuitry on the instrument cluster is the problem.
If i am right - then not much I can do .... but thought I would run by you guys who seem to seen EVERYTHING!
'86 Town car with electronic 'bar graph' Fuel Gauge.
More often than not - the reading is wrong for the 1st few mins. Usually a LOT lower than it should be - eg showing empty when tank is full. If I drive long enough (20 mins?) - it usually climbs and settles to the correct value.
If the engine is off, and I turn the key to ON, wait for Display is finished its power on sequence, then OFF
- gauge comes back to a different point each time.
And this is very common:
- Car off for a length of time
- Start and drive off. Fuel level is usually correct.
- Stop car for 5 mins at shops
- Restart car. Fuel Display = ZERO (!) for about 5 mins.
Diagnostics
1) This gauge is designed to flash 3 symbols if the circuit to the fuel sender is open circuit. It NEVER does that - unless I disconnect the rubber booted connector on the fuel tank.
2) Measure 12VDC on the 2 connectors inside that boot with ignition = ON. (Manual says 10V or more is fine)
3) Measure exactly the correct resistances with a multimeter connected to the two connectors on the fuel tank. eg: Empty fuel = about 10 ohms, and full tank = 190 ohms (This matches the manual values). While measuring - rock car up/down. Values stay steady (+/1 one or 2 ohms). No sudden jumps to high or low resistances (as I would expect with a worn variable resistor in the tank).
4) The way this is designed, higher resistance = More Fuel. So ... if I had a corroded (ie resistive) connector for example, I assume that the gauge would show MORE fuel than I have...but it shows less most of the time.
5) Connect a fixed resistor of about 100 ohms to the 2 connectors in the rubber boot. Ignition = ON/OFF. Fuel Gauge displays different values each time.
Conclusion:
- I think the sender in the fuel tank is OK and not giving bad readings.
- I think the circuitry on the instrument cluster is the problem.
If i am right - then not much I can do .... but thought I would run by you guys who seem to seen EVERYTHING!
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