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Thread: erratic speedometer

  1. #1
    Fuel Injected!
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    Aug 2012
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    265

    erratic speedometer

    94 suburban with 6395 pcm, stock drac and stock speedo. When I start off first drive of the day at about 15 mph the speedo goes full right and then back to normal. At about 40 mph steady state, if I lightly tap the gas ( 5 in vacuum change ) the speedo will go up 5 mph and come right back down as pedal down. It shifts as it should and goes from idle ve and spark at 3 mph as it should so I don't think it is a vss problem. I have reseated the plugs on pcm, tps, map sensor and drac. There is nothing abnormal in the way it drives. I will have to dig out my data logging stuff. It has run so well in the last long time my data logging is in the back of the shop storeage. Just wondered if anyone had run accross something like that. Also if you have thoughts.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  2. #2
    Fuel Injected!
    Join Date
    Dec 2016
    Location
    Colorado
    Age
    33
    Posts
    92
    Quote Originally Posted by myburb View Post
    94 suburban with 6395 pcm, stock drac and stock speedo. When I start off first drive of the day at about 15 mph the speedo goes full right and then back to normal. At about 40 mph steady state, if I lightly tap the gas ( 5 in vacuum change ) the speedo will go up 5 mph and come right back down as pedal down. It shifts as it should and goes from idle ve and spark at 3 mph as it should so I don't think it is a vss problem. I have reseated the plugs on pcm, tps, map sensor and drac. There is nothing abnormal in the way it drives. I will have to dig out my data logging stuff. It has run so well in the last long time my data logging is in the back of the shop storeage. Just wondered if anyone had run accross something like that. Also if you have thoughts.
    Did you check the circuit from the drac to the speedometer? If the trans is shifting fine then it sounds like its on just the speedometer circuit.

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