360 tachometer shows 2.5k more than actually rpm | FerrariChat
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360 tachometer shows 2.5k more than actually rpm

Discussion in 'Technical Q&A' started by sevak89, Jun 2, 2025 at 8:43 PM.

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  1. sevak89

    sevak89 Rookie

    May 31, 2025
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    #1 sevak89, Jun 2, 2025 at 8:43 PM
    Hello, my tach shows 2.5k more than the real RPM which I can see on my scanner tool. Idle is about 4k but it's actually at 1k. I'm assuming since the scanner sees actual value the problem might be with the cluster?
     
  2. yelcab

    yelcab F1 World Champ
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    #2 yelcab, Jun 3, 2025 at 8:50 AM
    Why don't you swap the sensors (TDC) left to right. See what happens. It's easy to do.
     
  3. sevak89

    sevak89 Rookie

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    #3 sevak89, Jun 3, 2025 at 9:17 AM
    Thanks for the reply, what sensor are we talking about? TDC? I've heard that to be top dead center is there another name for the sensor? Crankshaft sensor? There is 2 of those?
     
  4. Qavion

    Qavion F1 World Champ
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    #4 Qavion, Jun 3, 2025 at 10:14 AM
    Does you scanner identify where the rpms are coming from (LH ECU, RH ECU or instrument panel?)

    The crank (TDC) sensors feed into their respective Motronic ECUs and the ECUs send the data on the CAN Bus to the Instrument Panel. I don't know if a particular ECU is responsible for sending the data to the instrument panel. I was informed recently that the CAN Bus goes from the LH ECU to the RH ECU, then through the RH ECU to the other ECUs/Instrument Panel, so it's hard to say where the instrument tacho data is coming from.

    If your engine is running normally, shouldn't the crank sensors be ok?
     
  5. sevak89

    sevak89 Rookie

    May 31, 2025
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    #5 sevak89, Jun 3, 2025 at 10:20 AM
    Engine runs fine, I'm going to try to see if I can look at rpm of both banks and see if they match or one is wonky. If both sensors are reading good I would have to assume it's an instrument cluster issue?
     
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  6. yelcab

    yelcab F1 World Champ
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    #6 yelcab, Jun 3, 2025 at 1:19 PM
    That is a valid conclusion.
     
  7. 360trev

    360trev F1 Rookie
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    #7 360trev, Jun 3, 2025 at 5:25 PM
    One of the self diagnostic checks that an SD3 computer can do is to run a instrument cluster REV counter diagnostic check. I would be trying this next. It will set the rpm in a self test at each respective 1,000 rpm segment and count upward from there. I'm sure a lot of the aftermarket tools can do this too like the Leonardo and possibly even cheap dongles too.
     
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  8. Qavion

    Qavion F1 World Champ
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    #8 Qavion, Jun 3, 2025 at 6:47 PM
    I wonder if the F1 gearbox would behave oddly if it was getting excessive engine rpm data? I don't know how the engine ECUs process the rpm data to put it on the CAN Bus, but I assume that if one of the ECUs was not processing the rpm data properly, you'd get perhaps warning lights on the dash or some strange vehicle behaviour.

    The instrument cluster seems more and more likely to be the culprit, but it would still be interesting to know which ECU is providing data to the cluster (and if there is a backup if one source is completely absent).
     
  9. windsock

    windsock Formula 3
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    #9 windsock, Jun 4, 2025 at 3:14 PM
    My first suspicion would be someone either replaced the backlighting or replace the gauge faces and took the needle off and did not get it back on the right position.
    Trev has already told you how to self test the accuracy.
     
  10. Qavion

    Qavion F1 World Champ
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    #10 Qavion, Jun 4, 2025 at 4:42 PM
    Did the tach suddenly develop the issue or was it like that when you bought the car?
     
  11. sevak89

    sevak89 Rookie

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    #11 sevak89, Jun 4, 2025 at 8:11 PM
    I had a second look and the needle sits at 3k when the car is off. I'm assuming it moved during a previous repair or something. I'm going to remove the cluster and see if I can reset it back to normal. This car is new to me I got it with this issue and just noticed it sitting high when the vehicle is off.
     
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  12. Qavion

    Qavion F1 World Champ
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    #12 Qavion, Jun 4, 2025 at 8:39 PM
  13. sevak89

    sevak89 Rookie

    May 31, 2025
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    #13 sevak89, Jun 4, 2025 at 8:42 PM
    Perfect, thank you!
     
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