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That bloomin MAF connector!

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  • That bloomin MAF connector!

    So, I've been away for a couple of weeks, I come home jump in the car and drive off, almost right away I'm thinking the cars not going right.. Its just like it was on the way to cornwall, put your foot down but no real go, in fact it goes better at 0.5bar than at 1 bar of boost. As the boost comes up you get lots of wooshing noise but less power.. I try flooring it, it cuts out. Ok, so maybe I've got a boost leak but how? From being parked up for 2 weeks??
    I stop and restart a couple of times but its still the same, all whoosh and no go.

    So I pop the bonnet and resisting the temptation to reset the ecu again I just pull the MAF connector off look at it plug it back in, get back in the car, restart and its going fine again, I'm pretty sure if I now reset the ECU it will be back on form but what is exactly happening in this scenario???
    The connector is clean (done with Caig De-Oxit) There is no visible corrosion.

    All I can think is that somehow there's enough corrosion build up or galvanic action from the current passing through the MAF element or from the cleaning current at start up to cause a shift in the overall resistance of the MAF which gradually changes metering of the air mass and therefore the fuel mix. The Lamda helps the ECU to adapt to this for a while but eventually it gets too far adrift and goes off the edge of the mapping, the mixture goes completely wrong the turbo still blows but the car makes no power, it feels like it has a boost leak. Disturbing the connector is enough to remove the oxide or at least break through the film and normal operation is resumed untill it happens again a few weeks (or days) later.

    My next course of action will be to replace the MAF connector and crimp on new pins, I'm hoping the new plug comes with better pins (they're actually sockets, the pins are in the MAF) The old ones don't put much pressure on the pin so I'm thinking its pretty easy to get a bad connection. If not I'll find some proper AMP crimps that fit. I have 1/4 and 3/16 ones already.

    I wonder if this is the thing that sorts the car out when you wash the MAF too, its actually the unplugging and replugging of th3e MAF that sorts it out. I'm also reminded of how well the car goes after I changed the air filter and how I had to unplug the MAF to get to the filter.. Hmmm...

    So what do you think chaps? Am I on to something here?
    If you think I am or if you'd like to join in an experiment, I'd like you to go for a drive, stop, switch off, unplug the MAF, push-pull the plug on and off a few times, go for another drive see if its better, then reset the ECU (fuses out for 5 mins) go for another blast and post your results here.

    Lets see if anyone else has a funny MAF connector

    S2 Coupe 3B Project


    Ur quattro restoration

    S2 Avant

    Boost is the new rock and roll!
    sigpic

  • #2
    Originally posted by newsh View Post
    So what do you think chaps? Am I on to something here?
    I think, that your ideas are not bad. MAF output voltage is in 0-5v range, which is quite low voltage for penetrating stuff that lives on connector. ECU is very sensitive to that voltage changes, so additional impedance can mess up fuel mixture. However, more usual case is that wire breaks somewhere inside insulation. Then electrical gremlin permanently moves under your bonnet with family and friends . Real PITA to find. However it is usually followed by jerkiness and mysteriously appearing error codes, so it may be not your case.

    Changing/rebuilding connector is very good idea, especially if someone used to plug/replug it often, or (and) cleaned connector with something abrasive. Good point for the start.

    Sau
    200 20vt 88' 3b, human carrier
    CQ typ85 with AAN inside, see project blog at http://kwlw.blogspot.com

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    • #3
      So, nobody wants to join me on this experiment?




      S2 Coupe 3B Project


      Ur quattro restoration

      S2 Avant

      Boost is the new rock and roll!
      sigpic

      Comment


      • #4
        Remember...

        By removing the connector you have moved the wiring, there may be an intermittent contact in the wires somewhere?

        Leave the conector in and 'jiggle' the wires to it (technical term!) then go for a drive.
        These faults are the worst to find, big BTDT!!!

        Good luck.
        Carlos.

        On the look out for less bits for my s2 saloon project. Now supporting myself by shooting for my food. www.airgunforum.co.uk

        Comment


        • #5
          I don't currently have my car at hand to try any experiment like this, had no problems with mine so far tho.

          Problem with moving the wires also is if you do it near the connector unless its held on tightly could still disturb any gunk on the connections.

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          • #6
            Ok...the theory...please correct.

            The elements inside the MAF work by resistance, it being part of a voltage divider network(?)

            The element will have quite a high resistance to take into account wire length, connector resistance changes etc. With a constant current running through it a potential voltage can be measured at the ecu. This will change depending on the temperature of the element, so giving us a 'air flow value'.

            A small change in R may bring about some improvement, but the greatest change comes from something like an open circuit. This is all very difficult to describe in words withiout knowing peeps knowledge of electrickery?

            Does anyone know the R value and characteristics of the MAF elements?

            Pressure required to make an electrical connection is far less than a mechanical one.
            Carlos.

            On the look out for less bits for my s2 saloon project. Now supporting myself by shooting for my food. www.airgunforum.co.uk

            Comment


            • #7
              Originally posted by Flat on my back View Post
              The elements inside the MAF work by resistance, it being part of a voltage divider network(?)
              NO. The elements inside MAF is sophisticated piece of electronics, with voltage stabilizer, and there is some sort of microcontroller inside, which makes hot wire readings, adjusts them by temperature, and calculates linear air mass signal - voltage. Things are not so simple inside that black box...

              Sau
              200 20vt 88' 3b, human carrier
              CQ typ85 with AAN inside, see project blog at http://kwlw.blogspot.com

              Comment


              • #8
                FWIW I have had odd running problems - jerky running, no power etc, cured by unplugging and replugging the MAF along with ECU reset. There was another thread about this some time ago and I think bad contacts is an issue. I too have tried special contact cleaner without much success. Perhaps a MAF unplug should form part of regular underbonnet checks like oil/screenwash etc ?

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                • #9
                  can someone make a picture of the wiring that the MAF cables run through?I do have a spare RS2 95 wiring loom sitting around i could check(thourgh the rumble of my basement).The most obvious thing to do in cases like this is strip apart the plastic cover of the cables of the maf,then look for disturbances in the cables.(cut or about to be cut cables)

                  Another thing would be the plain bypass.By finding the complete rout of the cables,the easiest thing for the electrician mechanic would be to cut the cables from the connector up to the point of their furthest end,and replace them with new ones that we know they are OK.
                  can it be done??

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                  • #10
                    I had the same issue and i could cure it by moving the connecter it ended up a broken connection in side the MAF on the back of the pins and by moving it slightly it would move in the gell for a bit then would happen again

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                    • #11
                      I had a similar problem a few years back , and was always convinced that cleaning/reseating the connector made the difference , still do it every few months even now, why it works I'm not too sure, but a hypothesis could be ecu knows when this connection/signal path (whatever you wanna call it ) has been down/broken/removed and on such an event does some sort of reset to a table ? within the ecu ?, pure conjecture I know, but if somebody knows the inner working of the ecu/maf relationship It'd be good to read.

                      Anybody citing dendritic growth or "alpha particle errors" within the Maf will be heard...

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                      • #12
                        I have same symptoms exactly and usualy get the same result ,get a couple of weeks
                        of power and and then sluggishness ,ie 2 weeks ago ave mpg 21\22 very responsive
                        this week 17\19 sooty exhaust hesitant lots of noise and boost no go
                        sigpic

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                        • #13
                          As far as I can tell, the mass air flow sensor (MAF) for the ABY S2 is the same as that for the RR Urq, the 3B S2 and 200 20vt and the UrS4 and UrS6 (all same PN 034 133 471 K). The RS2 MAF is different (but similar).

                          As with all Audi electrical devices, the power is brought to the device in a female flat pin connector that mates up (no pun intended) with the male pins that stick out of the device that is to be powered, in this case, the MAF. In the case of the MAF, it's a flat six pin female connector or "terminal housing" in Audispeak.

                          The PN for this six pin connector was originally 022 906 233 A. However, at some point, it was dropped and replaced by 025 906 238 B. The female pins for this connector typically come two on a yellow covered pig tail wire. The PN for these female connectors is 000 979 133 or 133A for the 1 mm wide pins or 225 or 225 A for the 2.5 mm wide pins. The "A" is for the gold-plated version (slightly more costly but likely the ones you want if corrosion is a problem).

                          Hope that helps. Either that or use Stabilant 22.
                          RS2'd 93 UrS4 5 spd sedan
                          94 UrS4 V8 6 spd manual avant

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                          • #14
                            Thanks for the p/ns
                            Mine did it again this week, lots of noise and no go, the turbo is whooshing so loudly that you'd be absolutely convinced there was a boost leak but a quick wiggle of the connector and all seems well. This seems to work with the engine off, or running, no ecu reset needed. I really must replace this connector soon.

                            S2 Coupe 3B Project


                            Ur quattro restoration

                            S2 Avant

                            Boost is the new rock and roll!
                            sigpic

                            Comment


                            • #15
                              well i cleaned my connector last night with a peice of wet and dry and even put a little copper slip on it ,this morning the car ran perfectly again no hesitation ,full boost and better mpg totally differant from yesterday i didnt reset the ecu either.
                              sigpic

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