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  1. #1
    Join Date
    Nov 2005

    Default How to test diesel rpm sender and gauge?

    My 1976 Volvo MD11 is showing zero revs even when it's at full throttle and belching black smoke! I know it's running as it also makes a noise!

    Seriously though, how do I tell whether it's the sender or the gauge? Is there a simple test that I can do on either to see what response I should get, if any?


  2. #2
    Join Date
    Feb 2004

    Default Re: How to test diesel rpm sender and gauge?

    What are your volts and amps like ?

    Unless the charging circuit is OK it is possible that the tacho wont see the correct signal from the alternator.

  3. #3
    Brian_Moffat is offline
    Location : Port Napoleon, Port St Louis du Rhone, France
    Join Date
    Dec 2005

    Default Re: How to test diesel rpm sender and gauge?

    How about - you have stuffed your engine?

    Try under M for maintainence - it's in the dictionary

    Don't bother with useless questions - Let me give it to you in simple technical terms -

    1.You could not be bothered to service the motor.

    2. The motor is now stuffed.

    3. You are attempting to blame the fault on Electrics

    4. On your bike - sunshine

    5. you are going to be billed full rates - 120.00 Sterling per hour for an electronics engineer

    6. plus you will additionally be billed at 80.00 Sterling per hour for the diesel mechanic (s) - each

    7. Sunshine - we are just adding up the bill - Never be so stupid again.



  4. #4
    Sixpence's Avatar
    Sixpence is offline Registered User
    Location : Having a spot of Tiffins
    Join Date
    Aug 2005

    Default Re: How to test diesel rpm sender and gauge?

    No I am not out of retirement , but , oh your comments were so helpful , NOT , the guys in trouble and as usual , sh 1 t on him , yeh that helps

  5. Default Re: How to test diesel rpm sender and gauge?

    Dead easy this. got a multimeter? preferrably an analogue one?

    Know where the sender is?

    Set your meter to volts. Start your engine. put your meter across the sender, doesn't matter which way round. You should be getting a slight deflection at tickover. If it a digy then you should be getting either a low voltage or flickering digits.

    If this is ok, go to the back of your tachometer and try the same thing up there - but beware there are usually 4 wires if memory serves - ground, positive, backlight and signal. ground is usually black or brown, backlight is blue so on the othe two you will either get a full 12 volt reading (wrong wire - that's the positive) and the other should be the slight deflection/flickering - if so change the tacho. If not your wiring could be at fault - dodgy crimp terminal, trapped wire etc.

    Or get me in to fix it and I don't charge 120 an hour. Who the hell charges 120 an hour?


  6. #6
    Join Date
    Nov 2005

    Default Re: How to test diesel rpm sender and gauge?

    To all apart from Brian, thanks. Your suggestions are very helpful and I'll be doing some diagnosing tomorrow.

    To Brian, get off the forum and go sailing, maybe it'll help the BA.

    Boy, am I glad we don't belong to the same club.

    Cheers guys.

  7. #7
    MentalPause is offline Registered User
    Location : Lake District (closed for maintenance)
    Join Date
    Aug 2004

    Default Re: How to test diesel rpm sender and gauge?

    What Mogsey says - also double check for bad terminal connections, probably at the engine end of the wiring.

    Thats what it was with mine even though I didn't think it was that at first inspection, until I took them off and cleaned the sender terminals and crimped some new connectors back on, then it was ok.

  8. #8

    Default Re: How to test diesel rpm sender and gauge?

    Good response!

    This guy is a real worry but he is just showing how he operates. You go to him with a problem with your Tacho and he will charge you for fitting a new engine.

    I wonder if he talks to his customers in the same way?

  9. Default Re: How to test diesel rpm sender and gauge?

    You know what it is, don't you?

    The french have rubbed off on him. It's not his fault he's an arrogant cretin.

    *waits for the flames*


  10. #10
    john_morris_uk is online now Registered User
    Location : Home near Exeter, work in Hampshire, boat in Plymouth
    Join Date
    Jul 2002

    Default Re: How to test diesel rpm sender and gauge?

    Lots of engine RPM meters work off the impulses from the alternator.

    The sorts of questions that you need to be asking are:

    Is the alternator still charging? (Check the battery volts when the engine is running - should be 13.8 - 14.5 volts of thereabouts)

    Are the connections on the back of the alternator to the tacho still ok. (Wires fall off, dirty connections etc etc)

    Has the tacho still got its 12v supply? (Check with your multimeter on the wires going into the tacho etc etc)

    My tacho stops working when the alternator stops charging - its happened twice. Once when the bolt holding the alternator onto the block sheared, and once when a wire broke on the back of the alternator.

    Hope that this helps.
    [B][I]Wishing things away is not effective.[/I][/B]

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