Tachometric Relay | FerrariChat

Tachometric Relay

Discussion in 'Boxers/TR/M' started by jgmblair, Sep 20, 2019.

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  1. jgmblair

    jgmblair Formula Junior
    Silver Subscribed

    May 27, 2010
    715
    Winnipeg, MB Canada
    Full Name:
    Jeff Blair
    I've been chasing my tail a bit with hunting down some small electrical issues with my car. It's been a bit of a process over the past few years trying to reverse engineer some of the hacks installed by previous alarm, phone, and radio installs prior to my ownership. My symptoms started a few months ago with a hard to start then brief running, followed by a complete stall.

    I've found this previous thread quite informative

    https://www.ferrarichat.com/forum/threads/help-please-my-testarossa-starts-for-about-a-second-then-stops.97603/

    Im at the point where I think I need a new Tachometric relay as I can get the car to run by jumping the 87 and 30 to simulate a properly closed relay and I have confirmed the protection relay is functioning as I have +12v at the water thermoswitch red wire while running. I was hoping someone ;) might chime in to answer a few questions prior to me trying to find one.

    1. What is the proper function of the Tachometric relay with the key in the "on" position? I assume the relay will only close (87 to 30) when in the "start" position or when the key is released to the "run" position? I ask the questions as I have played around with a comparable fuel pump relay from an 80's BMW but it will run the fuel pumps with the key in the "on" position which I assume might cause some issues in a crash?

    2. Is there an ideal and measurable voltage of the signal being produced by the 7-12 coil to terminal 1 (BR wire)?

    3. How is this signal related to the engine speed sensor (Tach)? As described in this reply from Brian S.

    Simply put-

    the left bank coil will supply a signal to the tachometric relay (and tachometer) to let the system know that it is running, the tachometric relay supplies the signal to both fuel pump relays and keeps the thing running. If the coil does not give that signal, it will briefly run on the cold start injectors and 7-12 coil.

    I have found this fault in about 6 cars in my history FWTW.

    Brian

    4. Where can someone find a new Bosch 0280 230 006 or has someone found a suitable interchangeable relay?

    Thanks in advance.
     
  2. jgmblair

    jgmblair Formula Junior
    Silver Subscribed

    May 27, 2010
    715
    Winnipeg, MB Canada
    Full Name:
    Jeff Blair
    Anyone, Bueller, anyone!
     
  3. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    25,040
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    Haven't made this measurement myself as I have the later coils without the spade connectors, and I don't want to dig out my tachometric relay ;)

    One thing to try is making an AC voltage measurement between terminal 1 (the BR wire) and terminal 31 (ground) during starter motor cranking or engine running. Should be a non-zero AC voltage (i.e., 0 VAC would be a sign that the 7-12 coil is not firing).
     
  4. Jeff Pintler

    Jeff Pintler Formula Junior

    Jul 20, 2005
    537
    Richland
    Full Name:
    Jeff Pintler
    I have been searching for one of those also. Try entering to bosch part number at Ebay. I also did a search in Google images an found a Peugeot car that used the same unit and someone in England has a site with a modern electronic replacement. I have tried ordering from two venders and one posted back that the lead time was 17 months and they requested I cancel the order. The second source is in Latvia! and I have been waiting two months, only $40. My understanding is the Tach relay supplies 12 volts to the fuel pump relays once the engine is running by sensing the pulse of the 7-12 coil. When you are cranking over the engine with the starter, power is also supplied to the fuel pump relays, I believe. Check this PDF.

    I will post more when the part shows.

    Jeff Pintler
    89 348tb, 86tr, 99 360 3pedal
     

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