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TPS and Wack MPG gage

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    TPS and Wack MPG gage

    Looking for some input here, I'm going crazy trying to figure this out.

    Ive recently developed an issue with my early model 325e with s50. when I start the car, the mpg gage will read 0 like it should when the car is stopped. After a few seconds it will start going from 0 to 40 and back then eventually stay at 40mpg thinking the car is moving. It works fine once the car is moving. Variables:

    - speedometer works, so good speed input from diff.

    - idle does not increase while coasting. Symptom of speed to dme not connected.

    - randomly throws throttle position sensor code. Will clear after cycle of key.

    - tps resistance is in spec and all wiring is correct to tach, fuel economy, and vehicle speed (tapped from red/brn on obc).

    Any help would be greatly appreciated!



    Sent from my SAMSUNG-SGH-I317 using Tapatalk

    #2
    Si batteries?

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      #3
      Originally posted by mpowerful View Post
      Si batteries?
      They have been dead since I got the car.

      Sent from my SAMSUNG-SGH-I317 using Tapatalk

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        #4
        What should I expect to see voltage wise from the VSS signal from the cluster?

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          #5
          I think you may be over thinking this. It may just be the gauge. I have had to mix and match from multiple clusters to get all of my gauges to work.

          The MPG gauge I have in there now has behaved similarly once. But has been behaving since. Not sure what caused or fixed it though.

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            #6
            I have tried two tachs now. Same result. I am only getting 11.3vdc from the vss from both the obc point and the green plig on the back for cruise control.

            Sent from my SAMSUNG-SGH-I317 using Tapatalk

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              #7
              So I tried it again when I got home. In closed loop, the mpg rests at 0 with a smooth idle. When its warm the mpg gage will still fluctuate and idle seems to drop then catch itself abt once every 45sec. I also noticed that when the gage is stuck at 40mpg and I rev it, the needle will go back to zero then back to 40. What sensor could cause this in open loop that isnt already being used in closed? A new OEM TPS worked for abt a month. Then it threw the code but had all good test results per Bentley. I put on a third known working TPS and I still get random TPS codes. Anyone have any ideas? starting to run out of options here. Case of BEERto whoever can help me solve this!!

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