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How smooth is your 3B

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  • How smooth is your 3B

    Alright chaps,

    S2 is back on the road for this year following a headliner retrim. Although I'm not 100% happy with the retrim job I must admit the car looks a lot more fresh inside now. Anyhow, I digress!!

    The next issue I would like to iron out, if it is a genuine problem, is to get to the bottom of why my car feels kind of lumpy on the slightest off throttle openings, round the town where the car is moving in say 1st or 2nd between 1-3k it kind of surges or pulses, a real lumpy feeling and is most annoying. It's as is if it only likes going on boost everywhere which is perfectly smooth, vacuum driving not so nice!

    Now as you can imagine almost everything has been replaced on this car-

    TPS setup 0.3v - 4.7v

    Idles pretty good, there is a slight stumble but not sure if this is to do with the single mass flywheel. Also no boost or vacuum leaks and no codes.

    When I drive on a steady throttle in 1st or 2nd say at 2000rpm as an example, the AFR gauge fluctuates between 14 - 14.7, this corresponds to the lumpy feeling that can be felt.

    Is this how all 3B's drives or can you suggest something to look at that I may have missed.

    Surely they didn't come from factory like this.

    As always any help much appreciated.
    Last edited by gmac78; 20th May 2019, 16:56.

  • #2
    It should be smooth
    How did you test for leaks, whole inlet tract pressurised from MAF hose?
    How about PCV pipes and components, no leaks there? Have you replaced the PCV one-way valve?

    Have the injectors been flow tested?

    S2 Coupe 3B Project

    Ur quattro restoration

    S2 Avant

    Boost is the new rock and roll!


    • #3

      That's good to hear, didn't think it should be like that.​​

      I normally pressure test from the MAF, however yesterday i tested from the inlet pipe to throttle body as was thinking a vacuum pipe had come loose on the back of the inlet manifold. Since I'm running the Volvo turbo there are a few more bungs to fit so opted for the quicker test. It's not long since I tested from the MAF and all was nice and airtight. I think the problem lies elsewhere.

      The PCV was removed years ago and replaced with a catch can vented to atmosphere.

      I was using RS2 injectors but swapped them out yesterday for RS2 replicas which were bought brand new. I think it feels a wee bit smoother with these injectors but not by much. Having the RS2 injectors refurbed is a good call for the price of it. At least I could rule that out.

      Fun and games tracking down these wee gremlins!!!


      • #4
        The PCV one was valve would have been removed years ago with the rest of the pipework. I think?? Can't say I've seen it anywhere.


        • #5
          Could you perhaps nudge the issue by doing the following one at a time:

          a) If you temporarily disconnected and plugged the vac line to the FPR, or perhaps more likely;

          b) Disconnect the idle switch and/or the TPS,,,

          and drove it as above again, perhaps that would indicate if the source was in either of those directions (ignition timing or fuel pressure variability least from those sources)?


          • #6
            If PCV is removed correctly.
            The 20mm(?) connection at the MAF hose has been blanked off.
            The 8mm (?) spigot under the back of the IM has also been capped off.
            I presume all carbon can stuff has also been removed. The purge valve is usually left plugged into the loom to stop the code coming up.

            S2 Coupe 3B Project

            Ur quattro restoration

            S2 Avant

            Boost is the new rock and roll!


            • #7
              Ok guys, PCV removed correctly, been so long since I done it I couldn't remember what was involved.

              Vacuum to FPR removed and plugged. Still the same stumble/hesitation.

              Plug removed from TPS and driven, still the same.

              Going to try a new set of plugs, I believe some are more suited to the coil pack conversion than others. Currently running F5DPOR.


              • #8

                Re slow-speed drive-ability, how did you make out with some new plugs sir? If no joy, I wondered if you and Ajax1976 despite the motor differences, perhaps share a similar issue (his post yesterday):


                Might it be that there is also a shared mechanical aspect underlying this situation which, when you are at low to zero throttle but just barely on and off of it in a low gear (precisely when the required torque to propel the car is quite low), near lugging speed but not quite that slow, yet which causes the engine to, too quickly wind-up something(s), then rebound and repeatedly oscillate between accel. and de-accelerating (and thus changing the timing and fuel delivery between those two ECM modes), that might possibly have its' roots in either the centre diff wear that Error has mentioned elsewhere, or more hopefully, collective wear in all the CVs, or better yet perhaps just some slack or weakness in the drive-train mountings (i.e.: Snub, Eng. or Xmsn., Rr. diff., A-arm bushes), or a combination thereof?
                Last edited by Lago Blue; 20th May 2019, 17:40.


                • #9
                  Lago Blue,

                  Sorry for the lack of updates on this, been busy working on other vehicles.

                  So, since my last post I changed out the OEM RS2 injectors which if I remember correctly I purchased with around 80k miles on them, or so I was told anyway, and replaced them with brand new Siemens RS2 reps. This made a slight improvement to the idle, with less random stumbles felt and heard throughout the car. Out on the road, on the bare minimum of throttle input a stumble could still be felt, slow driving round the town was still not a smooth affair and kind of annoying!!

                  Next I changed out the plugs from F5DPOR which had maybe 10k on them, but had suffered some fouling when my oil stem seals were passing, to brand new OEM NGK PFR6Q that I had in a spare B5 S4 engine.

                  Fired the car up, and again an improvement to idle was immediately apparent. A lot smoother on tick over, the random stumbles that were previously felt were all but gone. Out on the road the car felt noticeably stronger and pulled with greater urgency, hard to describe really but mid to high revs had a marked improvement. I took a friend for a spin who is regularly in the car with me and he too commented on how much stronger it felt. I was really pleased with the results but since these plugs were not ones recommended for the car I ordered NGK BKR7EIX-11 IX which have been getting good reviews. These have still not arrived, didn't realise how long the delivery time was when I ordered them.

                  However, round the town, on the the smallest throttle openings the jerkiness/stumble is still there making a smooth constant power delivery unattainable. Once on the throttle whilst accelerating the car is perfectly smooth, so, as mentioned above I'm thinking the fault lies elsewhere.

                  My centre diff has a good amount of play in it, and I've been thinking, just as you mentioned above, it's this slack that I am feeling when the power is being transferred on and off with a constant minimum throttle opening.

                  I'll see how it feels once the new correct plugs arrive but I have my doubts if it will cure this issue.

                  I'm going to send the OEM RS2 injectors away for refurbishment, so intrigued to see what difference that will make.



                  • #10
                    Evening chaps.

                    New NGK BKR7EIX-11 plugs and refurbed OEM RS2 injectors fitted and still this stumble/hesitation continues.

                    What I've noticed now is that when first started from cold this stumble/hesitation is far more pronounced, as it warms through it improves but still there to a certain degree.

                    I removed the ISV to inspect the the associated hoses for any sneaky tares under the jubilee clips but none present, not yet anyway.

                    This is most annoying now, I had started to think the play in the centre diff had something to do with it but not so sure now.

                    Any further ideas?



                    • #11
                      Have you pressure tested the whole intake from the Maf hose?
                      ( I haven’t read the thread again )

                      S2 Coupe 3B Project

                      Ur quattro restoration

                      S2 Avant

                      Boost is the new rock and roll!


                      • #12
                        In my experience any slack in the center diff manifests itself in either 1st gear from standstill or especially reverse , mine blew up eventually , lol


                        • #13
                          No I've not re pressure tested from the MAF hose, it's a bit more awkward to do now since I'm running the Volvo 7400 turbo, really need to get under the car to fit bungs etc. Job for tomorrow just for peace of mind but almost certain it will be ok.

                          Just been out for a wee spin and decided to unplug the G62 coolant sensor which I replaced 4-5years ago as was thinking it was at fault but made no difference if I remember correctly. I noticed straight away that the car drops back down to idle a lot smoother and doesn't intermittently come close to stalling like it does with it connected. Or at least it never on a 10 mile run, could do with a longer spin to know for sure if the idle settles smoother consistently.

                          There's no current codes for this sensor but if I remember correctly it was changed out for an eBay variant, so could potentially be causing me some issues. I think I have the original sensor lying around somewhere so will refit that one and see how the car fares. Be nice if it was something as simple as changing the G62....


                          • #14
                            If you can get Vagcom on it, go to measuring blocks and you can see the temperature it’s sending the ECU, if it doesn’t agree with real life there’s your problem.
                            Actually when I first got my 3B the G62 wires were shorting inside the rubber boot!

                            S2 Coupe 3B Project

                            Ur quattro restoration

                            S2 Avant

                            Boost is the new rock and roll!


                            • #15
                              Alright guys.

                              Pressure tested from the MAF today and found a leak from number 5 injector seat. I have never noticed this before and is audible in a quiet garage from quite a low pressure say 0.2 bar. With soapy water sprayed on it, it bubbles until any residual pressure has depleted.

                              What's the best course of action for this, the engine was still warm after a wee spin this morning so tried to nip it up, however i didn't put too much effort into it as I'm afraid the seat will shatter which I don't want happening today.

                              The seat looks in good condition, can't see any visible cracks but the leak is from UK passenger side of the car. The injectors that were in it are my newly refurbed OEM RS2 with new O rings etc so no issues there.

                              Where can I buy seats from if required?