Tacho misreading revs

Terry Liddelow Dec 3, 2018

  1. Terry Liddelow

    Terry Liddelow New Member I am in australia

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    Hello,
    I have a 100 series 1HZ TD 4.2, best motor ever built by far.
    The two issues I have are as follows;
    1. The taco intermittently (no rime or reason as to when this happens) drops to almost nothing when idling, and then wont read correct when moving, for example will drop down to show 100 rpm, subsequently read ~1600 when doing 100 km, should be closer to 2100. It can go the other way and read way to high as well but a lot less frequently. Checked connections that i can find.

    2. I had a service conducted recently, following this, not directly but building, the engine starts to rock the car in idle when the aircon kicks in, say at ~700 - 800rpm. Its like there is a balance issue, the mechanic cant seem to find anything amiss. if i turn the aircon off the RPM's are not enough to make the car shudder, just around the 7 to 800 range.
    Thanks for any input.
     
  2. Rodger

    Rodger Well-Known Member

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    I may be comparing chalk and cheese here but my rev counter behaved very similar to your description. (60 series rev/c to match the engine). Once I changed the pickup sensor all was well and that was years ago.
    Can't comment on the aircon other than the compressor will take some power so maybe the cut in point should be raised but I have no idea if that can be done.

    Regards,

    Rodger
     
    Terry Liddelow likes this.
  3. StarCruiser

    StarCruiser Well-Known Member Supporter Guru I am in uk

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    On the AC, did you have that serviced too? Any regassing? Could your service have dislodged the idle up vacuum hoses (the 80 has these, I’m guessing the 100 too though not certain).
    Sounds like your tacho has an internal fault or a fault with whatever send the speed signal. If there has been water getting under the dash, this can affect tracks on the circuit boards. Difficult to say which but it could be either. Check connections. I’ve no idea where the tacho takes its speed from on the hundee. Sometimes it can be the alternator. The plug on the back of the alternator is known to get corroded and may be worth a wiggle/check.
     
  4. Terry Liddelow

    Terry Liddelow New Member I am in australia

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    Thanks Starcruiser,
    as to this not long after writing this question i was travelling to work and the motor started blowing an unbelievable amount of white smoke out the back, completely blocked out 4 lanes!!
    anyway turned the motor off and towed to mechanic. So just prior to Xmas rush he started pulling things apart, in the end the Injectors which i had reconditioned 18 months earlier turned out to be crap. bad job done by a bad tradesman.
    after replacing the injectors, cleaning the inlet manifold, all new seals everywhere, check the compression and valve tolerances all back together the motor runs like a dream, idles like new.

    But, always a but, no power, about roughly 50%! no smoke under load, no idle issues, standing still rev the engine to 4000 rpm no issues sounds perfect, but when driving there is just no power.
    So this explained the shuddering but now the question is what can cause the loss of power.
    Tacho seems to be back working for the time being anyway.
    Cheers
     
  5. StarCruiser

    StarCruiser Well-Known Member Supporter Guru I am in uk

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    Can you feel your turbo kicking in? Again, check the small turbo hoses and look for any splits in intake tubes. Check the turbo actuator for leakage.

    How old is the fuel filter? Look at changing it. There is a fuel sock in the tank which can get blocked. One way to check this is to disconnect the main fuel hose into the filter and blow back down the pipe. This will temporary dislodge some of the crud and let you know if this is the problem. Reconnect and reprime and see if things improve.
     
  6. Terry Liddelow

    Terry Liddelow New Member I am in australia

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    Thanks for the tips Starcruiser, the mechanic had another look and ensured the turbo was completely hooked up with hose and away we go!
    usually something simple to fix the issues.
    all good running like a dream again, even the tacho keeps working properly.

    Thanks for your input.
     
  7. StarCruiser

    StarCruiser Well-Known Member Supporter Guru I am in uk

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    Woohoo! :dance:
    Nice one Terry. Glad it’s sorted and thanks for letting us know. :thumbup:
     
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