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  • Throttle Position Sensor

    After trying to find the cause of some uneven engine behaviour at constant speed, I unplugged the throttle position sensor to see if it would be better or worse. It was much smoother. (As you would expect transient reponse was worse as the TPS is feed forward, so hard accel is slower basicly)

    So: Firstly I measured the resistance over pins 1 and 3 and it was 5.6Kohms (it should be 4k ohms), resistance across pins 1 and 2 varied between 0.8 and 6.4kohms. So even at this stage it was clearly not working right.

    Then I hooked it up to a data logger at work and could see that although the max voltage was ~5V and minimum was ~1V there was a big step in the middle of the range. Jumps from about 20% to 40%.

    So when driving along at constant speed it was stepping telling the ecu that the throttle was much more open than it really was.

    Moral of this story is when a garage says your throttle position sensor 'is fine', unless they have a plot of voltage v's position they have no idea if it fooked. Some garages will open to throttle slowly and look at the voltage - two well respected indys (probably the two most popular on this forum) did this and failed to spot the problem.

    New sensor is £51.67 +Vat from BMW, I'm picking my new one up tonight.


    Also just to note it is safe to drive without the TPS for diagnostic purposes as the MAF and Lambda sensors will keep the fuel mixture safe.

    Cheers,
    Craig
    Last edited by cragg711220; 04-01-2010, 12:33 PM. Reason: spelling
    Imola S50 1999

  • #2
    Fitted the new TPS last night and she's running much beter.
    Imola S50 1999

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    • #3
      Craig,

      Interesting post. What symptoms where you seeing before? I've had a problem with mine for several years where the engine occasionally runs unevenly when travelling at constant speed.

      I've had an ohmmeter on the TPS a few times, but have never managed to spot anything unexpected.

      The problem I have is very intermittent, and in fact, I can't remember it doing it at all in the last 12 months, but other times it'll do it more or less continuously.

      Paul

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      • #4
        Hi Paul, there were 2 main symptoms, the main one was driving at constant speed ~60mph, it feels just like a misfire and coming off throttle and back on clears it for a bit.

        The problem is the carbon tracks on the sensor get worn around the position of low throttle as this is where its used the most. I took mine appart, I'll attach a picture when I fiure out how!

        At constant speed at 60mph as you know you only need the slightlest amount of throttle so it's right in the middle of the worn area in the sensor.

        The other symptom was a light crackling in the exhaust when exiting low speed corners, I put this down to an exhaust sheild being slightly loose but when I disconnected the TPS (and now with the new TPS) the crackling has gone, so I think this was due to a over rich fuel mixture on throttle (because the sensor was telling the ecu the throtle is more open than it really is. Maybe I'll now see a fuel saving!


        When I checked the max and min voltage of mine it looked OK, when I checked the resitance it didn't match up with what bentley says but it was only when I hooked it up to a logger where I could get position v's voltage then I noticed the step in the middle of the range.

        My advice to anyone without access to a scope or logger would be to disconnect it and if the engine feels smoother then replace it. But bearing in mine the engine will have less poke without the sensor connected obviously.

        Hope that helps.
        Imola S50 1999

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        • #5
          Hmm I might be getting this when cold in say 3rd gear but I'm never sure if it's my stiff rear dampers giving that impression lol (kind of a faint bobbling sensation).

          What's the part no. for it?

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          • #6
            13637840383
            Imola S50 1999

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            • #7
              Hopefully not a silly question..but where is this part situated?

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              • #8
                on the end of the throttle butterfly spindle. Open the bonnet and its the first thing you see.
                Imola S50 1999

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                • #9
                  Originally posted by cragg711220 View Post
                  Hi Paul, there were 2 main symptoms, the main one was driving at constant speed ~60mph, it feels just like a misfire and coming off throttle and back on clears it for a bit.
                  That sounds very much like what I have - only a problem when the throttle is in its "cruising" position, and accelerating seems to cure it temporarily.

                  What's strange is that it's very intermittent, and I'd previously thought it was related to fuel as some days it doesn't happen at all and some days it happens all the time.

                  Next time it's having a bad day I'll try disconnecting the TPS.

                  Paul

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                  • #10
                    Did you fix this? I had a prolonged light throttle misfire problem a couple of weeks ago, driving it hard was fine, but idle was slightly rougher and light throttle there awas a misfire. Power was fine though. Took it out since then and it was perfectly fine!!?

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                    • #11
                      It certainly fixed mine a few months back. I used to get abit of a misfire when the engine was cold, especially on cold mornings when abit of damp was about which probably upset the worn tracks of the sensor and used to trigger the EML light at times.

                      Since ive changed it its been absolutely fine, not 1 problem since and only a 5 min job plus about £65!
                      2002 '52 S54 - Titanium Silver with 18" BBS LMs, AP Racing BBK, KW V3, H&R anti roll bars & ACS flippers (previously 2000 'X' S50 - Arctic Silver)

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                      • #12
                        I was experiencing the same issues relating to a "misfire" like sensation at a certain throttle position. I changed the throttle position sensor and it has eliminated the problem.

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                        • #13
                          This relates to the S50 I assume, as Craigs car.
                          S54 Titan Silver metallic. Black leather, most factory options including sunroof, Becker Cascade and Becker Silverstone changer.

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                          • #14
                            There is one on the S54 as well, I've read its well worth changing as a preventative measure given the age of the car. I picked one up from dealers but never got chance to fit it this summer
                            VIDEO or Journal

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                            • #15
                              Originally posted by cragg711220 View Post
                              13637840383
                              Fitted a new throttle sensor this weekend as the misfire was getting really bad at times; seems to have cured it now!!

                              I got it from http://www.bmminiparts.com/ , about £36 delivered. They list two parts, the part number I got was 13631402143 which was the same part number already on the car. See two switches listed for Part 8 here (
                              http://www.bmminiparts.com/DiagramVi...060&MOSP=48075)

                              Realoem list the 143 switch as for the M3 CSL only (http://www.realoem.com/bmw/showparts...=11&fg=40&hl=4) which is a bit confusing as my S50 had this part number fitted already. BMMINIParts said one has probably superceeded the other, but from the dates the 143 switch sounds like the older one, but then only fitted to the CSL which is the newest car, the 383 is most likely to be the newer part (it may be more durable, not sure). Either way mine seems fine now!!
                              Last edited by c_w; 10-01-2011, 04:38 PM.

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