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308qv tach signal

Discussion in '308/328' started by gonzo350, Jan 26, 2010.

  1. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
    Full Name:
    Myles
    Want to verify my tach reading with my multimeter (reads rpm), but where do I pick up the tach signal? Tried all 8 tabs on both coils....nothing, Ideas? (1984 308qv Euro)
     
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  3. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,335
    The brown wire from Pin 10 of the Ignition module goes to the Tach (-) as the tach signal. The ignition module uses the speed sensor for the information.


    ________________________
    http://www.FerrariWiring.com
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #3 Steve Magnusson, Jan 26, 2010
    Last edited: Jan 26, 2010
    If you are looking for a low voltage signal that has 1 pulse (or cycle) for each crankshaft revolution, I don't believe that sort of signal exists anywhere in your electrical system. Can you describe "my multimeter (reads rpm)" a little more? If your multimeter can also measure frequency (Hz or cycles/sec), and you know/count the number of teeth, N, on your flywheel ring gear (this thread, http://ferrarichat.com/forum/showthread.php?t=211033, indicates that N = 144 for a 308), and measure "Hz" between the two wires of the RPM flywheel sensor (measure between pin 2 and pin 3 at either ignition ECU, or at the intermediate connector, or at the RPM sensor connector), the result displayed on the multimeter can be translated into engine RPM:

    Engine RPM (rev/min) = Multimeter reading from the RPM sensor (cycles/sec) x 60/N
     
  5. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
    Full Name:
    Myles
    Paul & Steve thanks for the reply.

    Paul......I hate to ask this, but.....where is the ignition module? I appriciate the link to the wiring diagrams...they're just too small for me to read (damn old age!)

    Steve.....this is the multimeter I'm using...in a typical coil system, + to the coil and - to ground....but doesn't seem to work in this case.

    http://www.sears.com/shc/s/p_10153_12605_00920925000P?keyword=actron
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #5 Steve Magnusson, Jan 26, 2010
    Last edited: Jan 26, 2010
    OK, that specialty meter has circuitry built-in to do the math, but I don't follow this:

    because your OM schematic shows that each of your coils should only have 2 low voltage wires attached - not 8?! One coil should have a yellow wire (+12V) attached to terminal 15 and a yellow/black wire attached to terminal 1. The other coil should have a yellow wire (+12V) attached to terminal 15 and a green wire attached to terminal 1. Do you have something completely different (or are you trying to measure at the ignition Digiplex ECUs)? Normally, for such a meter you would connect one lead from the meter to terminal 1 (on either coil) and the other lead from the meter to ground (or maybe terminal 15, if the instructions so indicated).
     
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  8. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
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    Myles
    #6 gonzo350, Jan 26, 2010
    Last edited by a moderator: Sep 7, 2017
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #7 Steve Magnusson, Jan 26, 2010
    Last edited: Jan 26, 2010
    That's the right place (there are only two terminals on each coil even though they have multiple wires connected). What do your instructions say -- connect between terminal 1 (the green or yellow/black wires) and ground (the chassis or engine), or between terminal 1 and terminal 15 (the yellow wires)?
     
  10. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
    Full Name:
    Myles
    Measuring Engine RPM
    RPM refers to revolutions per minute.
    When using this function you must multiply
    the display reading by 10 to get actual
    RPM. If display reads 200 and the multimeter
    is set to 6 cylinder RPM, the actual
    engine RPM is 10 times 200 or 2000 RPM.
    To measure Engine RPM (see Fig. 14):
    1. Insert BLACK test lead into COM
    test lead jack.
    2. Insert RED test lead into
    test lead jack.
    3. Connect RED test lead to TACH
    (RPM) signal wire.
    • If vehicle is DIS (Distributorless
    Ignition System), then connect RED
    test lead to the TACH signal wire
    going from the DIS module to the
    vehicle engine computer. (refer to
    vehicle service manual for location
    of this wire)
    • For all vehicles with distributors,
    connect RED test lead to negative
    side of primary ignition coil. (refer
    to vehicle service manual for location
    of ignition coil)
    4. Connect BLACK test lead to a good
    vehicle ground.
    5. Turn multimeter rotary switch to
    correct CYLINDER selection.
    6. Measure engine RPM while engine
    is cranking or running.
    7. View reading on display.
    • Remember to multiply display reading
    by 10 to get actual RPM.
    If display reads 200, then actual engine
    RPM is 10 times 200 or 2000
    RPM.

    http://www.actron.com/publish/2004/06/07/pdf_english_16155.pdf
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    #9 Steve Magnusson, Jan 27, 2010
    Last edited: Jan 27, 2010
    (Assuming that you've got the probes in the correct holes on the meter, and the meter selector switch on the 4 cyl RPM scale - not the 8 cyl scale) This means connect the red probe to terminal 1 (where the green or yellow/black wire is connected) on one of the coils (doesn't matter which one).

    Touch the black probe to the (bare) engine cylinder head casting or a good ground point on the chassis.

    If you still get no result, then something must be wrong with the meter. Have you confirmed that it works in other ways -- like measuring the voltage between the two battery terminals?
     
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  13. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
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    Myles
    Steve.......this is one of those moments where you have to come clean....but you REALLY dont want to......the "hold" button was depressed! Brand new meter and I didn't even think about it! So no....not a defective meter....just a defective opperator! Thank you SO much for your help! (My tach reads 150 rpm high...)

    Myles
     
  14. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
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    Don't worry -- confession is good for the soul, and anyone who says they never made a mistake is fibbing ;)

    Are you saying that it's off a fixed 150 RPM at all RPMs, or does the difference get greater at higher RPM? (In a strange coincidence, my tach also reads about 1150 when the engine is really at 1000 RPM -- but I didn't check it at higher RPM.)
     
  15. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
    Full Name:
    Myles
    It's off a consistant 150 throughout the range, the error does not increase exponetialy with rpm.
     
  16. Paul_308

    Paul_308 Formula 3

    Mar 12, 2004
    2,335
    I don't have a manual for the Euro QV but mine are under the rug in the boot quite near the left sidemarker light. But I question your mission at this point. If you are on the short end of the learning curve and don't have a problem with the engine, I respectively add that idle curiosity might work to your disadvantage here.

    Readable wiring diagrams can be found, regardless of age.
     
  17. gonzo350

    gonzo350 Karting

    Apr 3, 2004
    207
    Lafayette Indiana
    Full Name:
    Myles
    Paul,

    Thanks for the response. I guess what you were calling the ignition module is what I call the digiplex...so I was getting lost in translation. As for my mission, I'm finishing up a complete bare block total rebuild and wanted to verify the accuracy of my tach for dialing in my high idle mixture. I appriciate your input.
     

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