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'88 Mondial tachometer...

Discussion in 'Mondial' started by CliffBeer, Oct 27, 2009.

  1. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
    2,191
    Seattle, Washington
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    Cliff
    I just did the belts and tensioners and other typical items on my '88 mondial - basically, the 30K service. The car hasn't been driven much in the last few years, perhaps 500-1,000 miles. Here's what's funky....

    The tachometer is reading, but very slowly. Meaning, it's reading out, but probably a third or less what it should be. In other words, what feels like about 3,000 rpm is reading 1,000 rpm and she sits on the needle at idle.

    The car is equipped with the motronic system. I've cleaned all visible grounds, checked the protection relay (functioning fine), cleaned the contacts on the tacho flywheel sensor and cleaned all the contacts I can find in/around the motronic ecu in the truck. What next? Diagnostic check on the flywheel sensor?

    Also, incidentally, the car feels a little sluggish and does a little spitting and farting when the throttle is applied more vigorously. The gas is reasonably fresh (and has Stabil) so I don't think it's old gas. New injectors, plugs, wires, caps, rotors, etc. all w/in the last couple of years and with very little use/wear.

    Any suggestions are much appreciated!
     
  2. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
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    Oh, and one more minor item - the "Antilock" light comes on periodically, particularly when the throttle is opened up a bit more aggressively and the car is starting to accelerate. I'm guessing the pressure in the ABS booster ball has decreased and the thing needs to be recharged or replaced. I don't see a valve for recharging so I'm guessing it's a replacement item. Any tips/suggestions?

    Thank you!
     
  3. TheMac

    TheMac Formula Junior

    Sep 5, 2009
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    Jon Mac
    By the sounds of what you describe, I have the exact same tachometer problem, also on an '88 Mondial. Relays are all clean on mine. I do not have the attendant ABS light problem, and the throttle is not sluggish. It's a little nagging problem that I have put on the back burner while I'm doing some other work.
     
  4. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
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    Anyone??

    Steve M, any chance you could share one or two of your expert thoughts on this one? You obviously know these systems very well - better than anyone probably!

    Regards,

    Cliff
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    (Your original post said "motronic" so I was unsure if you had a stock 3.2 ignition system or not, but, if yours is still the stock MicroPlex system, my comments are: )

    Based on the architecture of the MicroPlex (not motronic) ignition system, the trouble most likely is inside the MicroPlex ECU or the tachometer itself IMO. The food chain is:

    Flywheel sensors -to- MicroPlex ECU -which then- fires the coil primary windings and generates a separate signal to drive the tach

    Since you report that it basically runs quasi-OKish (i.e., the coil primary windings are firing), that indicates to me that the flywheel sensors (TDC & RPM) are basically OK. Unfortunately (or is that fortunately ;)), I haven't had the need to look at the tach signal going from the MicroPlex ECU to the tach so I can't say what is good vs bad, nor even if it is just an analog voltage or a series of digital pulses. Otherwise, the only other thing I can suggest is you try a different 3.2 V8 MicroPlex ECU or tach, and see if the problem is resolved with the new unit or not (which condemns the non-swapped component if the problem remains).

    Good Hunting!
     
  6. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
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    Hi Steve,

    Thank you, really appreciate the insights here. Very helpful.

    I only used the word "Motronic" because that's what's written on the label on the side of the single ECU in the rr trunk area. This looks like a more modern engine mgmt system that what's on my '82 308....

    In the past the tacho has done this once or twice before.....and just driving the car around for a few trips seems to resolve it (starts working normally). I was hoping this would be the case now but it seems determined to stay bogged down in molasses. I'm thinking it might actually be the tacho itself (as you suggest) but will move down the food chain starting with the signal to it.

    Thanks again!
     
  7. CliffBeer

    CliffBeer Formula 3

    Apr 3, 2005
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    #7 CliffBeer, Nov 5, 2009
    Last edited: Nov 5, 2009
    OK gents, quick follow up on this one.... Tach is working great now. Briefly:

    1. Remove the facia around the tach. It's pretty easy but be careful and gentle There are four push-in type retainer posts holding the facia surround around the tach. Gently pry the facia surroud off - use something like a 1 inch spatula to get under the edges and gently pry.

    2. Remove the tach. Once the facia is off you will see four screws holding the tach in. Remove these screws and lift out the tach exposing two light fixtures and three wires. Unplug the light fixtures and mark the terminal posts for the three wires (Gr, Bk, Br) and remove the wires.

    3. Open up the tach on the bench. There are four screws holding on the clear plastic face of the tach. Remove these and remove the face plate, noting the face plate is concave and should be reinstalled in the same orientation. Flip the tach over and remove the three screws on the back holding the guts of the tach into the housing. Be careful not to damage the needle or put a bunch of greasy fingerprints on the gauge face.

    4. Repair the tach. The tach is pretty much solid state with only a few moving parts that are essentially contact-less and/or self lubricating. However, you'll see there is a potentiometer with a little blob of silicon sealant on it (to hold the dial adjuster in place) which has a rheostat type contact. Mark the location of the rheostat with a fine marker. I believe this contact gets dirty or oxidized over time, and causes the gauge to read incorrectly, or not at all. Simply move the adjuster back and forth (gently) for a good 30 seconds and the contacts will self-clean.

    Reassembly is the reverse of the above. Your slow moving, lethargic tachometer will now read with proper accuracy and responsiveness. Sorry, I forgot to take pics.

    You can do the above, or pay Palo Alto Speedo to fix it for you for $200 plus shipping and two-week turnaround. Or, they might say your tacho is shot and charge you $500 for a "repaired" used one (they keep your old tach, clean the contact as above, and sell it for $500 as a used part). Having seen the inner workings of another well known gauge shop (not PAS), this is completely standard procedure for making more money and ripping off the automotive community. If some shop says your old ferrari part is shot and wants to sell you a refurb or new part, always be sure to get your old part back so they can't run this type of scam.

    Side note: some gorilla had already been at the tach at some point previously. He had broken off the retainer posts for the facia surround, put the clear face plate in backwards, and broken off two screw posts for the face plate retainer.
     
  8. TheMac

    TheMac Formula Junior

    Sep 5, 2009
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    Alberta
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    Jon Mac
    Great post, Cliff, terrific detail even w/o photos. I have got to find some time to put aside to do this job, it's one of those little things that I can live with, but would really rather put right, and soon.

    How long did it take you?
     
  9. Inowownone

    Inowownone Formula Junior

    Jul 22, 2005
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    Tom W.
    My Tach seems to work fine at idle, but seems to max out at 3,000 when I know I am pushing the throttle more than that. I wonder if it is the same problem that Cliff describes fixing above? Comments welcome.
    87 328.
     
  10. peterdavid911

    peterdavid911 Formula 3

    Apr 9, 2012
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    Great thread, thanks Cliff,

    I have an 87 3.2 and have the exact same problem with the rev counter but also my Speedo does the exact same thing so I really have no idea of my revs and speed. Does your Speedo work ok? I will take both units out and see.

    Maybe some contact cleaner would also help?

    Has anyone else fixed a lazy Speedo?

    Thanks.
     
  11. Inowownone

    Inowownone Formula Junior

    Jul 22, 2005
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    Speedo seems to be fine at all speeds


     
  12. afterburner

    afterburner Formula 3
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    #12 afterburner, May 1, 2013
    Last edited by a moderator: Sep 7, 2017
    Funny. 12h after reading your article, Cliff, my tach started to act up, or down... clearly getting very lazy. Fixed it your way and it worked, thanks for sharing your experience. Done the same to the speedo, whose needle moves slower up to speed than the car - accelerating briskly and then holding the pedal on a level road showed the needle reaching that speed later than the car; and same same vice versa. I also added a drop of WD40 into the hole at the backside centre piece. Here the pics, rpm first, then speedo.
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  13. nino calamita

    nino calamita Karting

    Sep 21, 2011
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    Chesterfield, UK.
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    Mine is the opposite, it bounces all over the place. on idle it reads anything around the 3,000rpm and say at a steady 60mph it bounces around 2,000rpm. Took it out and altered the pot but no difference.
     
  14. afterburner

    afterburner Formula 3
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    Nino, sounds like a connection issue. Since you had it all out on the instrument side, it's probably on the ignition side... unless the tacho does have an electronic issue.
     
  15. peterdavid911

    peterdavid911 Formula 3

    Apr 9, 2012
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    Hi Urs, hope all is well, great pictures which always helps.

    In the photo I can just make out a small black pen mark on the left next to the metal arrow on the potentiometer, did you literally move that metal arrow by pushing it back and forth to clean the contact inside it?

    You mentioned that you added WD40 in the hole in the backside center piece but I’m not sure what you mean by that, was that on the reverse side of the potentiometer or was it somewhere else in the mechanism?

    Just about to do mine this weekend.

    (By the way, the sunroof still works perfectly, couldn’t have done that without your help!)

    Thanks.

    Peter
     
  16. afterburner

    afterburner Formula 3
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    #16 afterburner, May 2, 2013
    Last edited by a moderator: Sep 7, 2017
  17. peterdavid911

    peterdavid911 Formula 3

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    Fantastic!

    Thanks very much.
     
  18. afterburner

    afterburner Formula 3
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  19. Inowownone

    Inowownone Formula Junior

    Jul 22, 2005
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    Hi Urs,
    Do you have any pictures of how to remove the tach? Would it be the same on a 328? No responses from the 328 board. :)
    Thank you for your guidance.
    Tom in Texas.
     
  20. Inowownone

    Inowownone Formula Junior

    Jul 22, 2005
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    Hi Peter,
    Please take a picture of the removal. Of your tach. I tried pulling on the surround ring of the tach - but it doesn't want to come off. I might be too gentle. :)

     
  21. afterburner

    afterburner Formula 3
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    Hi Tom

    I think the 328 instruments are fixed from the back via a U-shaped bracket that pulls them in to the hole. You probably have to remove a nut on the instrument's backside and then you can pull it out from the front of the panel. How to get there I don't know... The Mondial is entirely differently constructed, closer to the Testarossa for example.

    Sorry I can't really help you...
    Cheers
    Urs
     
  22. Inowownone

    Inowownone Formula Junior

    Jul 22, 2005
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    Thanks Urs.
    I'll wait on a response on the 328 board.
     
  23. peterdavid911

    peterdavid911 Formula 3

    Apr 9, 2012
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    Hi Tom,

    Urs is absolutely right that the 328 and Mondial dashboard instruments binacle are constructed very differently and dont have similarities in taking them off.

    However, I have some good news for you though, i have a 308/328 DIY owners guide as a pdf file and it shows how to remove the instruments to replace bulbs. It starts on page 92. PM me your email address and i will email it to you. It should be the answer you wanted:)

    Good luck with it.

    Cheers.

    Peter
     
  24. afterburner

    afterburner Formula 3
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    Jun 20, 2008
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    Would anybody know whether that potentiometer is where the speedo and tach get adjusted for the correct read out? Before I try... thanks for your replies!
     
  25. afterburner

    afterburner Formula 3
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    Jun 20, 2008
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    Just in case someone is interested: Turning the potentiometer clockwise increases the instruments reading relative to the input, and anti-clockwise reduces its readout.

    So, if your car goes slower than indicated, turn the potentiometer anti-clockwise.
    If your car goes faster than indicated (as was the case for mine, by about 10%) turn the pot clockwise.

    Good luck with the trial'n'error!
     

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