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How to test rpm sensor? 700 1990

posted by  Piper109 on  Sun May 11 06:37 CST 2008
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last visit: Mon Aug 1 19:15 CST 2011
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I have just bought a non running '90 740 wagon. I dont have it home yet and I will have to tow it 230 miles.

It has a history of sometimes starting but when shut down will not restart for a day or so. The owners have given up on it.

I have read in the FAQ the 3 most likely culprits being the fuel pump relay.
RPM sensor on the flywhee and the Radio suppression relay.

I figure I can eventually find a way to hot wire the relays temporarily to eliminate them as causes but is there a way to test the RPM sensor to know whether or not it is bad. Does it fail open circuit? Does if fail short circuit?

If I put a meter on it on the ac voltage scale and crank the engine over am I likely to be able to tell?

I think it has Regina ignition as it has quite a big black box on the drivers side wheel well.

This is my first gas engined Volvo and it seems in good enough condition to make it run, with about 160k on the clock.

Thanks for any help and advice.

Steve








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    How to test rpm sensor? 700 1990

    posted by  Piper109 on  Fri May 16 00:12 CST 2008
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    Thanks for the info.

    Well I have the car home now. I towed it. As soon as I got it home I charged the dead battery it cranked. Eventually it reached the point when it would no longer start. I removed the fuel pump relay and resoldered it. It started right up after that. Did I fix it or are there other things I should do?

    I did the test using the diagnostic box and it showed me 132 which is improper battery voltage. As the charger was on it, I ignored that code.

    cheers, Steve







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    How to test rpm sensor? 700 1990

    posted by  rstarkie on  Tue May 13 01:52 CST 2008
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    last visit: Fri Oct 24 10:14 CST 2014
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    You can remove the RSR and use a piece of wire to jumper the connector. Use the wire to complete the circuit between the two heavier wires in the connector.

    Sorry I can not tell you which relay of the two on the passenger's shock tower is the RSR. The other is for the fan on the radiator. If you jumper one and the fan comes on the other one is the RSR.

    Many people just swap one relay for the other but of course that assumes the fan relay is good and you probably don't know that.

    Randy








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    How to test rpm sensor? 700 1990

    posted by  austi012 on  Sun May 11 10:35 CST 2008
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    If what you're really asking about is the crank position sensor mounted at the flywheel, yes, there is a way using the on board diagnostics. The procedure is given in the Chilton's manual.. Anyways you put the diagnostic probe in port 6, press the button in some combination, and then crank the motor. It should come back with a specific series of flashes that tells you if it's OK.

    I've mislaid my manual for the moment but if I find it, I will post the procedure given therein. The bright side is, there IS a way.








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      How to test rpm sensor? 700 1990

      posted by  someone claiming to be joe on  Mon May 12 20:54 CST 2008 [RELATED]

      At $29 just replace it and be done with that potential problem, they all fail eventually. Reach down past the distributor , its a 10mm bolt, simple swap out.
      Ditto on the relays, get new ones, it should drive home.







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