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Thread: Tachometer needle jumps sometimes - cause?

  1. #21
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    Quote Originally Posted by 82DMC12 View Post
    Hey guys, update time. I actually replaced my alternator, and problem didn't improve, in fact it got worse! Here's a video after about 30 minutes of driving. I still have a slightly elevated idle problem I need to sort out, but as you can see the tach is going nuts. It doesn't show up on my Actron meter.

    I will check the connections on the back of the binnacle one more time. It's been said the tach itself is probably bad (the resistor on it perhaps). Is there anything else to check short of replacing the tach gauge?




    https://youtu.be/W3Y_2wEeZ_M
    I had the intention of going in and checking the ground for the instrument cluster. I believe it is tied into the ground bolt that is on the corner of the centre console, but not 100% sure. I was going to trace that out better once I got in there. But check the grounds for the instruments is what I would suggest.


    Sept. 81, auto, black interior

  2. #22
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by Ron View Post
    Curious as to what color the spliced harness wire was.
    The spliced wire was the black ground wire on the main plug. Maybe someone tried to install a backup ground? Anyway the wire was no longer there by the time I got the car. I don't think the ground could be the problem because all my other gauges and instrument lights are working fine and not flickering. What do you think? I'm thinking the problem is probably somewhere on white slate or green or the tach itself is bad.

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    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  3. #23
    Gone Fishin' Ron's Avatar
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    Quote Originally Posted by 82DMC12 View Post
    Hey guys, update time. I actually replaced my alternator, and problem didn't improve, in fact it got worse! Here's a video after about 30 minutes of driving. I still have a slightly elevated idle problem I need to sort out, but as you can see the tach is going nuts. It doesn't show up on my Actron meter.

    I will check the connections on the back of the binnacle one more time. It's been said the tach itself is probably bad (the resistor on it perhaps). Is there anything else to check short of replacing the tach gauge?




    https://youtu.be/W3Y_2wEeZ_M
    I'm leaning toward the W/S or tach as well.
    Maybe coincidence, but it getting worse after having the binnacle off and other work might indicate a bad connection.

    Anyway, if you don't find anything when you check out the connections again, remove the tach and hook it up to the coil, eliminating the wire harness and connection problems... (Connections are the same as with the Actron, except you will need to connect a hot (+) wire also.)
    TachHookup.jpg
    If you are uncomfortable doing this with the binnacle off, try on another vehicle...


    EDIT: Forgot to answer: I think the resistor could make it read wrong but not vibrate. You would be hard pressed to find another one...

  4. #24
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by Ron View Post
    I'm leaning toward the W/S or tach as well.
    Maybe coincidence, but it getting worse after having the binnacle off and other work might indicate a bad connection.

    Anyway, if you don't find anything when you check out the connections again, remove the tach and hook it up to the coil, eliminating the wire harness and connection problems... (Connections are the same as with the Actron, except you will need to connect a hot (+) wire also.)
    TachHookup.jpg
    If you are uncomfortable doing this with the binnacle off, try on another vehicle...


    EDIT: Forgot to answer: I think the resistor could make it read wrong but not vibrate. You would be hard pressed to find another one...
    Thanks Ron. I will have my binnacle apart next week installing a new plexi lens. Maybe I'll try this tach hook up trick and see what I find. What do you think about the "trigger / stator air gap" - have you seen such a thing out of spec on a DeLorean and possibly cause this? I had my distributor apart this winter and replaced the pickup coil but it seems like there's only one way to put it back together and I didn't notice anything that can go out of adjustment during that process.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  5. #25
    Gone Fishin' Ron's Avatar
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    Quote Originally Posted by 82DMC12 View Post
    Thanks Ron. I will have my binnacle apart next week installing a new plexi lens. Maybe I'll try this tach hook up trick and see what I find. What do you think about the "trigger / stator air gap" - have you seen such a thing out of spec on a DeLorean and possibly cause this? I had my distributor apart this winter and replaced the pickup coil but it seems like there's only one way to put it back together and I didn't notice anything that can go out of adjustment during that process.
    YW!
    Yeah, they can act odd if not installed to specs, but it seems it would be more consistent anyway....Unless the dash tach is way more sensitive than the Actron, I wouldn't think the trigger would be the culprit. And even if, I would expect the engine to be cross/misfiring, ether of which should be noticeable when listening to the engine.

  6. #26
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    A distributor with bad gaps on the impulse coil will mess up the idle. Very important to get it gapped right. Any time you take the distributor out you should check the gaps. The rotor is soft metal and bends easily.
    David Teitelbaum

  7. #27
    Senior Member 82DMC12's Avatar
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    Quote Originally Posted by David T View Post
    A distributor with bad gaps on the impulse coil will mess up the idle. Very important to get it gapped right. Any time you take the distributor out you should check the gaps. The rotor is soft metal and bends easily.
    David,

    What would the symptoms be of this "rough idle"? I definitely have something weird going on with the idle quality, aside from this jumpy tach. I assume the idle quality would be "rough" all the time and not intermittent?

    I actually ordered a smoke machine so I can try to finally zero in on my idle issues after a valley dive this spring.

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  8. #28
    Senior Member 82DMC12's Avatar
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    Tomorrow I'll take video of the idle so you guys can hear what I'm hearing.

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  9. #29
    Senior Member 82DMC12's Avatar
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    OK, I followed Ron's advice and installed my tachometer directly to the coil. I found that the needle continues to jump sometimes when hooked up that way. I then double checked with the Actron external tachometer and I don't see the same jumpiness happening. I think that pretty well proves that the tachometer electronics are faulty.

    Any comments?

    https://youtu.be/btd9xXf0YAk

    Sent from my Pixel 3a using Tapatalk
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Olathe, KS

  10. #30
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    Quote Originally Posted by 82DMC12 View Post
    OK, I followed Ron's advice and installed my tachometer directly to the coil. I found that the needle continues to jump sometimes when hooked up that way. I then double checked with the Actron external tachometer and I don't see the same jumpiness happening. I think that pretty well proves that the tachometer electronics are faulty.

    Any comments?

    https://youtu.be/btd9xXf0YAk

    Sent from my Pixel 3a using Tapatalk
    So... does one rebuild a tach? Or can a new one be purchased from one of the vendors?


    Sept. 81, auto, black interior

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