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  • RS2 Overboost and surging issue

    I am experiencing an overboosting issue. The engine boosts strong to 1.5bar up to 2nd gear but once in 3rd it overboosts to 1.8 then cuts back to 1.5 and continues to surge up to 1.8 and back to 1.5 through 4th gear and up. I've replaced the N75 valve which fixed a problem I was having with the turbo fluttering but the surging problem persists. I smoke tested the vacuum lines and replaced a few vacuum hoses that were leaking. There does not appear to be any more boost leaks.

    I've inspected the waste gate diaphragm and it looks fine.

    The main change I've made is installing a turbo back Supersprint exhaust with a straight downpipe so the cats have been removed. Could this be causing the turbo to boost to quick for the ECU to respond? The RS2 is chipped with a set of PRJ chips.

    Any ideas what the issue could be?

    Thanks,
    Dave

  • #2
    It’s possible you have a leak that doesn’t appear till pressure gets above 1 Bar, smoke is good but not as good as pressurising the inlet tract to 1.5Bar.
    Otherwise yes, removing the cats can definitely cause overboost if a chipset is mapped near the limit. I had exactly this on my RS4 (also mapped by PRJ) when the stock exhaust was changed for a full Miltek without cats.
    However, it would only overboost occasionally when I really slammed the throttle and then it would drop into limp mode.

    S2 Coupe 3B Project


    Ur quattro restoration

    S2 Avant

    Boost is the new rock and roll!
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    • #3
      Originally posted by newsh View Post
      It’s possible you have a leak that doesn’t appear till pressure gets above 1 Bar, smoke is good but not as good as pressurising the inlet tract to 1.5Bar.
      Otherwise yes, removing the cats can definitely cause overboost if a chipset is mapped near the limit. I had exactly this on my RS4 (also mapped by PRJ) when the stock exhaust was changed for a full Miltek without cats.
      However, it would only overboost occasionally when I really slammed the throttle and then it would drop into limp mode.
      Thanks Newsh.

      I'll retest with pressure and see what happens. If it is being caused by the removal of the cats, would a Manual Boost Controller help limit the boost to 1.5 and stop the surging?

      Comment


      • #4
        You could use a boost controller (either mechanical or electronic) instead of the ECU to set max boost, but you would lose the ability of the ECU to reduce boost if there is a fault and therefore mask a problem which might damage the engine.
        I wonder if you have a stronger than stock spring in the WG?
        Try disconnecting the WGFV (N75) and report back on how much boost you get, it should be 0.4 Bar if the WG has a standard spring.

        S2 Coupe 3B Project


        Ur quattro restoration

        S2 Avant

        Boost is the new rock and roll!
        sigpic

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        • #5
          Hi did you solve the RS2 Overboost and surging issue.

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          • #6
            Originally posted by Canadian RS2 View Post
            Thanks Newsh.
            I'll retest with pressure and see what happens. If it is being caused by the removal of the cats, would a Manual Boost Controller help limit the boost to 1.5 and stop the surging?
            Dave did you see this rear diff lock post?

            Originally posted by A80Avant View Post
            vaccum leak found!
            which also means that a boost leak is also sorted

            RS2'd 93 UrS4 5 spd sedan
            94 UrS4 V8 6 spd manual avant

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            • #7

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              • #8
                I just realized I never closed the loop on this one. I ended up replacing my PRJ chips with the stock set and that fixed the surging issue. The tune was most likely mapped to the limits and removing the cats and installing the Supersprint turbo back exhaust was too much for the tune. It feels really good though with the free flowing exhaust and the smooth boost.

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                • #9
                  Unfortunately it is how it is - most likely the boost PID needs to be adjusted after exhaust modifications.

                  Well hey, there's prjmod on m232.org if anyone feels like it. I don't anymore unfortunately.
                  http://tuner.ee - http://www.facebook.com/tuner.ee

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                  • #10
                    Originally posted by prj View Post
                    Unfortunately it is how it is - most likely the boost PID needs to be adjusted after exhaust modifications.

                    Well hey, there's prjmod on m232.org if anyone feels like it. I don't anymore unfortunately.
                    there's some support for ya.


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                    • #11
                      Im no tuning expert or nuffin but this seems like a good reason to keep the maf in the tuning equation. That is unless you wanna retune everytime you do anything to your car that changes the ve. Now i know why this guy's so busy.

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                      • #12
                        Originally posted by dr.strangelove View Post
                        Im no tuning expert or nuffin but this seems like a good reason to keep the maf in the tuning equation. That is unless you wanna retune everytime you do anything to your car that changes the ve. Now i know why this guy's so busy.
                        Both people who spoke in this thread do not have anything against me, because both had purchased Stage 1 software/chipsets for original cars. Indeed, both cars used and still use the MAF.
                        For both of them the Stage 1 software/chipset worked perfectly well when the car was stock and they were happy with it. Once they changed the hardware, the boost PID needed to be retuned, as simple as that.

                        MAF and VE have actually nothing to do with this. It's simply reduced backpressure on the wastegate thus making the WGDC pre-control map that is meant for the stock exhaust inadequate with the tuned exhaust. On the RS2 most likely drilling out the cap and winding the screw back a couple turns will solve the overboosting issue completely. On the RS4 it's more difficult - while the actuators are adjustable, doing it on the car is nearly impossible without taking the engine out. Actually it's quite easily possible to adjust the RS4 remotely, as the logging is much better on it. The RS2 Stage 1 chipset does not have a single prjmod patch in it. It's just a tune.

                        As for you - It's wise to know what you are talking about before opening one's mouth and looking very silly indeed.

                        Generally when you purchase a tune for a stock car that doesn't give you magical rights to free tuning once you change hardware.
                        But hey, you are free to take prjmod, and tune his or anyone elses car for if you like. I'd dare say my support is second to none, since I made thousands of hours of work available at no charge.
                        http://tuner.ee - http://www.facebook.com/tuner.ee

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                        • #13
                          Originally posted by prj View Post

                          MAF and VE have actually nothing to do with this. It's simply reduced backpressure on the wastegate thus making the WGDC pre-control map that is meant for the stock exhaust inadequate with the tuned exhaust. On the RS2 most likely drilling out the cap and winding the screw back a couple turns will solve the overboosting issue completely.
                          Well stock tunes don't boost beyond their set points when you change the exhaust. Just a more open tune?

                          Originally posted by prj View Post
                          As for you - It's wise to know what you are talking about before opening one's mouth and looking very silly indeed.
                          As for me, I'll open my mouth whenever I want thank you. If people waited until they knew it all no one would say anything and discussion would cease.

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                          • #14

                            Originally posted by dr.strangelove View Post
                            Well stock tunes don't boost beyond their set points when you change the exhaust. Just a more open tune?
                            Oh really?

                            As is clearly evidenced by these two cars, that's exactly what happens when you change exhaust on stock tune. The reason they actually go into limpmode, is because unlike most out there my first step on a Stage 1 tune is not 0xFF-ing all safety.

                            As I said. Prjmod is open, make better tunes (if you can), make them available for free, I don't care.

                            Tbh I don't think you even have the slightest clue what setpoint, actual and feed-forward PID control is nor have you ever tuned a car.
                            That's fine, but that's why I said you might want to *think* about being quiet when the subject matter is over your head and you have nothing constructive to add.

                            Attacking me personally will get you absolutely nowhere apart from looking stupid, as IDGAF.
                            Last edited by prj; 6th September 2018, 17:27.
                            http://tuner.ee - http://www.facebook.com/tuner.ee

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                            • #15
                              Originally posted by prj View Post

                              Oh really?

                              As is clearly evidenced by these two cars, that's exactly what happens when you change exhaust on stock tune. The reason they actually go into limpmode, is because unlike most out there my first step on a Stage 1 tune is not 0xFF-ing all safety.

                              As I said. Prjmod is open, make better tunes (if you can), make them available for free, I don't care.

                              Tbh I don't think you even have the slightest clue what setpoint, actual and feed-forward PID control is nor have you ever tuned a car.
                              That's fine, but that's why I said you might want to *think* about being quiet when the subject matter is over your head and you have nothing constructive to add.

                              Attacking me personally will get you absolutely nowhere apart from looking stupid, as IDGAF.
                              I'm not the expert, you are. NevertheIess, I've never had an overboost problem with my stock chips or the stage 1+ ones I bought off ebay for like $40 and there were plenty of mechanical nuances from the factory setup, including exhaust variations. Based on this experience and knowing that there are more closed-loop programs that are more sensitive to physical/mechanical differences, I'm arguing that your tunes likely fall into this category. Now I'm sure that there are advantages to this approach, including performance since the tune can be optimized for a specific application. As well, there are obvious commercial advantages. The downside is having to deal with you again or just cutting their losses and moving on.


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