Quote:
Originally Posted by bob12
Your instrument cluster being in an '89 740 is almost a certainty a VDO. After this time the most likely cause of a flickering/bonkers/iratic fuel gauge is the small pcb built into the back of the gauge itself has developed a fault. This can be either a bad solder joint or a duff electrical component. If you can find a working one anywhere (unlikely) the easiest cure is to replace it.
Other causes can be a faulty in-tank fuel sender, a poor input connections/earth usually at the back of the cluster on the blue plastic distribution circuit/s. It is unusual for the blue blue plastic circuitry to fail. If it has it is likely it will be obvious to the eye.
If the car has not been used much you can get problems with the resistance slider inside the in-tank sender.
If you can locate the right Volvo Green Book (TPxxxx) online you can test the input/output resistance values for the fuel gauge at the cluster. I have one somewhere and if I locate it I will put up it's TP number. Bob.
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The fuel gauge on my 740 is erratic, but I just live with in and do what I always do (and my dad did) was reset the trip counter to zero when I fill it up and I know roughly how many miles I've done when I need to fill up again.