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Solving Optic Engine RPM Channel problems

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  • Solving Optic Engine RPM Channel problems

    When troubleshooting RPM logging problems what are the most common reasons for malfunctioning?
    - pickup 800-OP-MAG
    - cable 800-OP-CABLE
    - logger itself?

    Our symptoms are: in logs we see RMP going wildly up and down. Sometimes it seems to be correct. Other channel is dead.
    I understand that a dead channel lives in darkness, but the other one: how is it possible that revs go suddenly up - would a light leak into optical cable cause that or is the logger itself in suspect?

    Next time we are able to fire up after 2 weeks so what kind of tests we can perform before D-day?

    Is there a procedure to test pickups?
    I was thinking of building a pulse generator to output a lookalike pulse to test pickups. What kind of current and voltage is needed? How about waveform?


  • #2
    Re: Solving Optic Engine RPM Channel problems

    The most common problem with the optic engine RPM is the 800-OP-CABLE itself. Quite often, the ends are not trimmed correctly which prevents the signal from being transmitted properly from the inductive RPM pickups to the data logger itself. On the inductive pickup end, the optic cable should be a straight cut with a fresh razor blade, while the end of the cable which goes to the logger should have the clear optic cable stripped back 1/8" - 3/16" and should go into the logger about 1/2" or more. This is because the signal being generated in the inductive pickup is forced down the end of the cable, while inside the logger, we look across the cable to read the signal, hence the need for the exposed tip. If your inductive pickup does not have a collet-style connector and nut, meaning that it was manufactured before April, 1996, it will also need to have the same exposed tip as described for the data logger end.

    I have rarely seen wild fluctuations on the optic signal, as it's a fairly simple circuit. However, if the inductive pickup lays on top of the coil, it will pick up interference and create erratic signals similar to that which you have described. Make sure that it is hanging freely on the primary wire.

    In the case of the dead channel, check to see that the pickup is generating a signal. With the car running, take the optic cable loose from the pickup and see if there is a red light being emitted from the pickup. If not, it is dead and will require replacement. If it does generate a light, then check the optic cable with a flashlight to ensure that light is being transmitted properly from one end of the cable to the other. Sometimes the cable can get routed in such a way as to kink or fracture the fiber optic, preventing the signal from reaching the data logger.

    As I mentioned, the best way to test the pickups is to look either in the end of the optic cable entering the logger or in the end of the pickups themselves to confirm that there is a red light being transmitted to the logger when the engine is running. Our test unit here at Racepak consists of an old points-style magneto which spins at 7600 RPM. We check the inductive units and cables both visually for the red LED signal, and using a Racepak Pro data logger to confirm the proper value.

    Let me know if you require any further information.

    Todd Paton
    949-709-5555 ext. 1652


    • #3
      Re: Solving Optic Engine RPM Channel problems

      Hi Todd

      The troubleshooting continues... Now we have both signals there, but they have 0.3-1.0 degrees difference even when both inductive RPM pickups are in same red coil primary lead. The shape of advance graphs are the same, but the Optic1 is always above Optic2. At 8000 RPM difference is 1 degrees and idle about 0.3-0.4.

      I have swapped optic fibers at logger end, but it did not change the situation. Optic1 has more advance.

      In Racepak Optic is compared against TDC so that should be ok. However I noticed that there is only 2 pulses/rev setting... Why is that? Shouldn't there be 4 pulses/rev since this is 8 cylinder 4-stroke engine we are talking about? However the logged RPM is ok, not half...

      The MSD PN7570 graphic editor shows that our trigger pickups are correctly aligned (within 0.1-0.2 degrees) if this has something to do with this...

      I'm running out of ideas.


      • #4
        Re: Solving Optic Engine RPM Channel problems

        Optic 1 and Optic 2 Timing will always lag behind the delay box outputs. The inductive RPM signal generated from the pickups is not clearly defined. The RPM reading is accurate, but different pickups generate the signal at different amperages. This is why I only use the Optic timing channels if the delay box input is not present (ie: bad cable). It provides an approximate view of the timing curve, but will not exactly match what you have programmed into the MSD; that will show up on Delay Box 1 and Delay Box 2 Timing.

        Since we only pick up the negative pulses from the coil, we have to set the channel parameters for 2 pulses/rev. That is why the RPM reads correctly with those values.

        Let me know if you have any other questions.

        Todd Paton
        949-709-5555 ext. 1652