Ferrari 328 tachometer reading half speed. | FerrariChat

Ferrari 328 tachometer reading half speed.

Discussion in '308/328' started by yelcab, Jan 1, 2020.

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  1. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    My 328 tach is reading only half speed. I understand that there is an electronic component, possibly a counter, that is bad and needs to be replaced. Does anybody know what this component is, looks like, or any other information?

    Second question: What are the differences between a US Tach and a Euro Tach? Why would any sane engineer design two versions for a tach?
     
  2. Freddie328

    Freddie328 Formula Junior

    Jul 29, 2013
    291
    Herts, UK
    Full Name:
    Richard
    There is a small adjustable resistor pot that is accessible from the rear of the taco. The finger gets dirty and this causes the taco to read low.
    You can normally fix this by firstly marking its position then turning it with a screw driver whilst applying contact cleaner. After cleaning adjust it back to the original position. You will notice a wax seal but this is easily dislodged by the action of turning the finger.
    Worked on mine!
    There is a post somewhere about this.
     
  3. PT 328

    PT 328 F1 Rookie
    Silver Subscribed

    May 1, 2005
    3,955
    Are you certain the engine is running on both banks? I had a similar issue when I had a pinhole sized burn mark on a plug extender. The car was running on one bank. Changed the bad plug extender and all was well again.
     
  4. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    I am very certain my car is running well, except that the tach is exactly 1/2 speed. There is no plug extender on my car. They were designed out by a set of custom ignition wires.
     
  5. Freddie328

    Freddie328 Formula Junior

    Jul 29, 2013
    291
    Herts, UK
    Full Name:
    Richard
  6. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    OK Freddie, I am going to try that out this next week. By the way, I understand what you said about the Speedometer place. Even with a minor problem, they rebuild the whole unit.
     
  7. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Ok, to close this off. Taking advantage of the Coronavirus lock down, I changed the oil and coolant on the 328 today. Then, I removed the instrument panel...

    side comment: really? This is the best way to design how the instrument cluster attaches to the dash?

    … off came the lights at the four corners, and then the two screws and two bolts. Wiggled the instrument cluster out, detached the connector to the tach, undid two thumb wheels at the back, and removed the tach.

    1. Carefully removed the front bezel, glass, and lock ring
    2. Detached the three spade connectors at the back of the tach
    3. Unscrewed the three little black screws at the back of the tach, and the inside guts of the tach falls out the front.
    4. Looked and found a small potentiometer, 1/2 inch in diameter. Removed the glob of glue, marked the original position
    5. Used a small screw driver to exercise the potentiometer over its whole range for 30 seconds
    6. Reassembled the whole thing

    And then put the tach back in the car. Careful not to drop the bolts behind the holes. The use of some sticky compound to keep the bolts attached to the screw driver is recommended.

    Test drove it and … by God, it is working, for today anyway.

    Done, next project !
     
    Cmsdk, Cirorsi, Saabguy and 1 other person like this.
  8. Saabguy

    Saabguy Formula 3
    Silver Subscribed

    Mar 28, 2012
    1,753
    Shreveport, LA
    Holy **** Batman! It's never that easy! Congratulations, explain problem, get concise fix directions, apply those to problem, problem solved!
     
  9. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Hah. The guy at Palo Alto made it sound like an electronic component needing to be replaced. There was nothing that sophisticated inside this tachometer.
     
  10. st@ven

    st@ven F1 Rookie

    Aug 4, 2008
    3,275
    Netherlands
    Full Name:
    Steven
    This inspired me too. And also being home due to Corona i Did the exact same job today. Will put it all back in the car tomorow and anxious to see if this fix is the real thing.
     
  11. Cirorsi

    Cirorsi Formula Junior

    Nov 10, 2016
    790
    Louisiana / Lac du Saint Sacrement, NY
    Full Name:
    Steven
    Mitch,
    Did you happen to take a pic of the back of the bezel? Are the tabs at the 12/6 and 3 and 9 positions? Did you use a plastic pry bar or a thin screw driver to remove the facia?
    My tach reads lazy after 3200rpm so I'm eyeballing this project. thanks, Steven
     
  12. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    There is one locating tab for the bezel at 6 oclock. The lock ring is not location specific and can spin around all day long. Use a small flat head screw driver to get it loose in one spot and work your way gently around it. Eventually it comes free.
     
  13. Cirorsi

    Cirorsi Formula Junior

    Nov 10, 2016
    790
    Louisiana / Lac du Saint Sacrement, NY
    Full Name:
    Steven
    Thanks Mitch!
     
  14. st@ven

    st@ven F1 Rookie

    Aug 4, 2008
    3,275
    Netherlands
    Full Name:
    Steven
    short spin result: it worked. Let's see if t continue to work as it was an typical "now-and then" issue
     

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