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Thread: Can Improper Tach Signal Output Frequency Fry PCM ?

  1. #1

    Question Can Improper Tach Signal Output Frequency Fry PCM ?

    Hey guys, working on a mystery here.

    Customer Came in with a 1969 Camaro with a 2010 LS3 Engine, Auto Trans, the PCM running it is a 2007 Trailblazer SS. Car was built a long time ago, and I dont know by whom...

    Car is pretty well put together and has been tuned before locally.

    Were doing some general maintenance, tune up ETC. He also asked us to help fix his Tach signal on the stock dash as it's working but not reading the proper rpms.

    I read on HP tuners that you can change the Resolution, and get the tach to read differently, so I attempted it.

    Resolution came in with a setting of 15 High and 15 Low, I changed to 6, no change...
    I tried resolution of 3 high and 3 low, no change in tach readings.
    Just to see if the tach would do anything differently, I tried 200 High and 200 Low (max allowable value is 0 to 255).

    Now car will not fire up. I put a value of 200, Course not thinking any ill effects could happen max allowable is 255, and this is the tach signal output...

    So.. Went back to stock 15 as it came in on, still wont fire up. I have Fuel, but to spark. I can still hook up to the PCM, I can tune and read. Still wont fire up... Checked fuses, all good.

    So. Any ideas?

    Thx !

  2. #2
    update.... Car runs now. WTH ! I let it sit for 20 minutes and simply walked up to it and attempted start up, fired right up...

    Very Interesting. Perhaps another underlining issue here other than what we did... Freaky !