I have a 1989 740 GL wagon with 154K on the odometer which has a odd fuel gauge behavior.

When I accelerate the fuel gauge reads higher than what I believe is in the tank or is the true reading.

When I brake the gauge drops significantly.

Both conditions return to what I think is the correct reading while driving at a normal speed and is stable.

When the car is at rest and idling the gauge tends to read low; once underway the gauge reads what I think is the correct amount of fuel for the mileage covered from filling the tank.

The variation does not go much past 1/4" or so in either direction of what I believe is the true reading. So if the tank is 3/4 full it does it in that area of the gauge or if it is 1/4 full it does this in that area of the gauge.

The gauge is working as it does slowly go down as the fuel is used, but it just does this odd behavior when either braking or accelerating.

While it is not a major issue I would like to correct this if it is possible.

Our other 740's gauge acts normally and is totally stable so I know that the gauge on this car is generally reading the correct amount in the tank for a given amount of travel.

Steve B Calgary AB

My '87 745 gauge will vary slightly depending on the angle of the grade,however I think your sending unit may be compromised. The plastic or metal tube that holds the potentiometer could be fractured but still attached by the wires.

On the other hand the internal tank baffles may be damaged.

The potentiometer "wiper" has a tendency to wear out, there is info about this in the FAQ's.

Most likely you'll have to do some exploratory surgery on the unit.

I recently finished installing a new sending unit and now know more than I ever wanted to!

It seems that the fuel gauge float is closer to the rear of the tank, so this fluctuation would be expected. Maybe there is a difference in the two gauges that delays the reading in one, so you don't see it. I think the fuel gauge also shows a "dumbed-down" reading. I remember a 1989 Ford Tempo I had that the temp gauge would move whenever the thermostat opened and closed and when the fan went on and off, which was kind of neat.
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1992 745 approaching 500k km