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Jumpy Tachometer 900 1994

I have a 1994 960 Wagon with 256,000 miles. It is the B6304-S 2.9 liter in-line 6 cyl. When idling and with the car in drive the tachometer will occasionally read "0" . Sometimes at highway speeds the tach will jump from around 2500 RPM's to around 3000 RPM's. And it might do that a few times until it setles back down.

My question is what might be causing this? Could it be the crank sensor? And if it were does the tach affect the shifting of the tranny? The tranny is the AW 30/40.

Maybe a seperate topic: The tranny seems to shift well but sometimes kind of abruptly. And if I am starting out the tranny goes from first to second OK, but when shifting to third will jump back to second and back to third again. And then third to fourth (OD) seems OK.

Thanks for the help!

e r i c








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    Jumpy Tachometer 900 1994

    Like Spook states, I had that very problem, the occasional jumpy needle while the idle was fine. Installed a new RPM/crank sensor have not seen it in almost a year.

    DanR 94 964 263,000 miles (29,000 on the new engine installed a year next week)
    --
    DanR








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    Jumpy Tachometer 900 1994

    Dear e r i c,

    Good a.m. and may this find you well. If the crank sensor has not been changed, at 256K miles, it does not owe you a nickel. It likely is the source of the inconsistent tach readings. The wiring to the sensor deteriorates, leading to intermittent operation. Usually, that causes the engine to stop running. This is not a hard part to change on a B230F engine. I've never done this job on a B6304 engine. See the FAQs, under Features, above.

    It is also possible that the tach's inconsistent operation is rooted in a loose or oxidized connector, in the circuit from the pick-up (on the differential) to the instrument. You'll need a wiring diagram to trace the circuit.

    As to the tranny, have you had it flushed recently? Flushing, replaces all of the fluid - about 9 quarts - in the transmission. Draining the fluid in the pan - about 2 quarts - is not enough.

    The trans fluid should be a bright pink. If it is brown, orange, black, etc., it needs to be changed. There is a procedure in the FAQs, that I think will work on an AW30/34. I've done the flush procedure on an AW71. It would be well to use fully synthetic fluid, if you plan to keep the car for yet a while. Otherwise, standard fluid will do.

    Hope some of this helps.

    Yours faithfully,

    spook







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