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328GTS Intermittent Tacho Issue

Discussion in '308/328' started by Knowazark, Jan 23, 2005.

  1. Knowazark

    Knowazark Rookie

    Dec 22, 2004
    43
    New Zealand
    Full Name:
    Ade & Steve
    Howdy

    We have an intermittent issue with the tacho in our 1988 328GTS. On occasion it reads about 1000rpm too low. Normally, if you start the car and the tacho's reading low it will continue to read low until you stop the car and re-start it, but occasionally it will change from 1000 rpm too low to correct (or what I assume is correct) or back.

    Is this the classic tacho problem characteristic of 3.2 cars, or is this something else? Poor earth connection? Internittent failure of a component in the electronic gauge?

    Any ideas?

    Steve
     
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  3. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
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    Greg
    Same symptoms. I have seen advice to clean up earths but the only real fix is to Yank the Tacho and send it in.

    No one here knows which electronic part goes which is a pity as many of us in countries outside the US live with ths problem as its a mission to send the unit to the states for a "simple" fix. While we do have local tacho guys here I do not trust them to try figure it out. I would prefer to remove the part myself and send it in with a specific instruction on what part to replace.

    Removing the Unit is done by removing the 4 corner outer lights on the instrument face to find the 4 face screws behind them.

    Let us know what part was fixed if you get it done.

    Skin.
     
  4. TOM B

    TOM B Formula 3

    Jul 24, 2003
    1,038
    Orange County, NY
    Full Name:
    Thomas Buckley
    I had the exact symptoms. Remove the tach and send to Palo Alto Speedometer in California. 2 day turnaround and $159.00 USD and I haven't had a problem since.

    Tom
     
  5. Knowazark

    Knowazark Rookie

    Dec 22, 2004
    43
    New Zealand
    Full Name:
    Ade & Steve
    OK, so its the classic tacho problem.

    I realise that some people have had satisfaction from Palo Alto Speedometer, but there's no way I'll be sending my tacho internationally for an indeterminate period for what amounts to a simple fix. As well as the risk of never seeing the instrument again, I have to face the prospect of not being able to drive the car for weeks, if not months.

    Any ideas regarding the actual fault and the fix would be deeply appreciated.

    Steve
     
  6. Mike328

    Mike328 F1 Rookie
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    Oct 19, 2002
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    Nobody has ever posted the exact component that gets replaced. I called Palo Alto Speedo and they were vague about it (I wonder if they were intentionally so).

    Another alternative is "MOMA" in Albuquerque, NM. Very well reputed, even outside of the southwest region.


    --Mike
     
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  8. Knowazark

    Knowazark Rookie

    Dec 22, 2004
    43
    New Zealand
    Full Name:
    Ade & Steve
    Damn! I was kinda hoping that someone would know what kind of witchcraft these speedometer technicians get up to .... at least generally so I could point the local instrument techies in the right direction. I'll chat with some local guys in our club and see if I can get further.

    If I find out what gets replaced then I will let y'all know.

    Steve
     
  9. Gatorrari

    Gatorrari F1 World Champ
    Silver Subscribed

    Feb 27, 2004
    13,778
    Georgia
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    Jim Pernikoff
    I have a tach problem myself; mine has read about 50% of reality ever since I bought the car.

    I've heard good things about Palo Alto Speedometer, but I'm wondering: isn't there anyone in the east that can do the job as well?
     
  10. f355spider

    f355spider F1 World Champ
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    May 29, 2001
    17,112
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    Hugh G. Rection
    Since the invention of overnight delivery, it really makes no difference where the business is located. What IS still important is that they do the work properly and timely.

    Dave
     
  11. f355spider

    f355spider F1 World Champ
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    May 29, 2001
    17,112
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    Steve,
    You can call Helmut at PAS and find out his current turn around times...usually around a week. You can drive the car without the tach...no problem, I did it while I waited for mine to return. BTW, he turned mine around in 3 days, if I remember correctly. I understand your hesitation with international shipping, but pack it securely, and insure it. That or find a local speedometer shop...I'm sure they could figure out what is wrong with it.
     
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  13. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
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    Greg
    The bunch of young snotkops at my local speedo shop insist that they want the car , not just the unit dropped off for a day or two.. Like there is no way.... im going to do that. They will pull my car through their asses. So i suppose until i find out what part needs fixing i will be doing 120 Km ph/ @ 1500 RPM.

    Skin.
     
  14. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
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    Greg
    I was bored yesterday so i took the tacho out. Quite fiddly getting the four 'corner' indicator lights out without scratching the matt black instrument panel.

    After that the unit came out easily and took it in to my local guys this morning. We shall see and i will ask and tell.

    He felt that it might be a mechanical linkage in the tacho owing to the fact that it always reads low but not consistently in the same place each time.

    He drew my attention to the fact that the needle was on 500 RPM and would not go down to 0 rpm even if he shook it a bit. I never noticed this before.

    He seemed pleased that the black face was loose on the white plastic body ie he could get into it easily enough.

    He asked if there were two coils ( one for each bank of cylinders) and i answered .. "dunno". (Still dunno.)

    He seemed pacified by that response and said he would call within a week.

    Skin.
     
  15. TOM B

    TOM B Formula 3

    Jul 24, 2003
    1,038
    Orange County, NY
    Full Name:
    Thomas Buckley
    Yes you have two coils and yes it is normal that your tach does not go below 500 RPM.

    Tom
     
  16. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
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    Greg
    They also asked what ignition it is, ( Marelli ?) is there an ECU ? does its get its pulses / signals straight from the coils or from the ECU ? etc.

    If anyone can give me this and any other relevant info, they have promised ( seeing as their market is so small in ferrari guages here ) to let me know what was wrong so i can let you all know how to fix it.

    BTW my car is a swooningly gorgeous 89 328GTS, Eurostyler :)

    Thanks
    Skin.
     
  17. Mike328

    Mike328 F1 Rookie
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    Oct 19, 2002
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    OK. I cracked open the 328 wiring diagram (not a bad little manual), and figured out the answer to your question.

    Bottom line:
    Module #26, the "Electronic Ignition Control Unit" [Page 11] has a brown-striped-black wire leading from it directly to the rev counter (tachometer), which is module #44 shown on pages 19-22.

    Also, according to the technical specs I have for the car, ignition system is a Marelli Microplex MED806A. This is corroborated by Keith Bluemel's book Original Ferrari V8 (which probably used my tech specs manual as the source for its info anyway).

    By the way, I had tach problems too, although mine is the infamous 50% of actual reading problem. I bought a new one from Ferrari UK (who were running a special on rev-counters), and just swapped it out. While it's out, I suggest upgrading the lighting (see http://www.ferrariclub.com/faq/dashlights.html).

    I still have my old tachometer by the way, if anyone's interested.

    Hope this helps!


    Take care,

    --Mike
     
  18. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
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    Greg
    Thanks Mike.

    They said they had it on the bench and they realised that it was not a 4 cylinder calibration ie 2 x 4 cylinder with a signal from each coil. My telling them that one wire comes from an 'electronic ignition control unit' confirmed this for them.

    They said that it - "ran well on the bench up to 4000 RPM and then it seemed to saturate and "fall away" as if it was getting too much signal ".
    They said that so far the board and its components checked out fine.

    They will investigate further.

    Skin.

    ( i can see whats coming... they are going to want the car for a few days..:(
     
  19. italia16

    italia16 Karting
    Silver Subscribed

    Jan 28, 2004
    120
    I had the same problem with a 86 328 and started a thread a few months ago on the topic. Mine would start out low and then jump up to normal later. Sometimes it would go back down too.

    After cleaning the battery terminal, it was much better but would still happen sometimes. But after I took on a long drive (160 miles), I did not have a problem for a couple months. Now, it is back only at startup/warmup, maybe because I only drive it 40-50 miles every week or two.

    So I think it has to do with not driving it enough. Or it could be something with the Florida humidity since I have a similar problem on my Nissan and never did when I lived in California. On that, it reads fine most of the time but the needle quickly jumps up and down sometimes.
     
  20. f355spider

    f355spider F1 World Champ
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    May 29, 2001
    17,112
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    Hugh G. Rection
    Dude, it's broken...get it fixed. Mine was similar...messing with cleaning the plugs and stuff would improve it for a short time...then bad again. Finally sent it in....no more problems.
     
  21. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
    Full Name:
    Greg
    Not a complete one but .. the local tacho and speedo guy called saying his is 80% sure he has found the fault. He says that there are a few fine caps on the board but in particular there is a "large" "electro cap" which seems a bit intermittant.

    He is ordering a new capacitor and will fit and test. I told him i must have the thing back dead or alive by the weekend for a car show. So i should know by friday exactly what he fixed or failed to fix. :)

    Skin
    Doing my bit for P.O.P
    (power to the people.)
     
  22. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
    Full Name:
    Greg
    Today he calls and says he fixed it. He says its the calibration pot not the cap.
    He says its basically a carbon resistor which carbons up if it sits for a while.
    ( Like the slide volume control on an old radio that crackles when you adjust the volume.)
    He says he just cleaned it up and its behaving fine. Cost two hours R410.00 or $ 68.00 US
    He insists that every component on the board checked out fine as well as all mechanical linkages in the tacho.

    I will fit and test it this weekend. Hope it works and hope this helps everyone.

    Skin.
     
  23. Mike328

    Mike328 F1 Rookie
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    Oct 19, 2002
    2,655
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    Great info!

    I have a spare tach... I might open it to see if I can't see where the calibration POT is...

    Very interesting info... If it's true, Palo Alto Speedometer has a great little business going for them :p.
     
  24. ric1241

    ric1241 Rookie

    Mar 6, 2004
    25
    I can well imagine that the vibrations that are normal might cause an adjustable pot to give trouble. If this is the case, the best fix would be to solder in a fixed resistor of the correct value once the calibration setting has been determined.
     
  25. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
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    Greg
    I installed and tested the tacho Friday night. It works flawlessly. Nothing i ever did before worked at all. ie cleaning earths etc.
    I'm convinced that the source of the problem was addressed.

    For those who wonder if theirs is fine, in fifth gear you get 33.6 km / h per 1000 RPM.

    My tacho never bounced around, It just read consistently low all of the sudden. I only noticed when i hit the rev limiter but it was only indicating 5500 RPM. The loss of the tacho was a serious blow for me as i loved watching the needle spin around and i usually change as it sweeps by 7000 RPM.

    Happy again. ( Now i only have to find the leak and regass my aircon and i have a 10 point car.)

    Skin.
     
  26. Knowazark

    Knowazark Rookie

    Dec 22, 2004
    43
    New Zealand
    Full Name:
    Ade & Steve
    Thanks for the info Skin

    Will contact a local instrument place and ask questions regarding calibration pots and cleaning.

    Invaluable information!! Many thanks.

    Steve
     
  27. Skindiver

    Skindiver Karting

    Apr 22, 2004
    203
    JHB SA.
    Full Name:
    Greg
    You are welcome "knowazark" and "mike328"

    Now if the gallery would all just quieten down now, so i can hear myself...

    Skin.

    "Hail to the king, baby" !!

    PS. The calibration pot is where you select either 4 cylinder or 8 cylinder signal input.
    Apparently ours are set for 4.
     
  28. f355spider

    f355spider F1 World Champ
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    May 29, 2001
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    Gotta agree with you there! ;) One thing though, to open it, requires removing the metal trim around the bezel. This is a pretty delicate procedure, and if you damage the trim bezel, I seriously doubt you could ever source a replacement....I would still probably send it to a professional....but knowing the problem now...one could perhaps negotiate that fee a bit!
     

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