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Lack of magic (boost) - UrS4

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  • Lack of magic (boost) - UrS4

    Hi guys. Not seeing more than 1.7 bar of boost? No error codes and no boost leaks. Checked all important vacuum lines and all is in order. Throttle burried, will go to 1.7 and sit there. Car doesn't misfire.

    what are symptoms of fuel pump being on its last legs?

    there seems to be leak new exhaust manifold, could that cause issues?

    '93 Audi 100 Avant - R.I.P
    '92 Audi UrS4 Avant - SOLD
    '93 Audi UrS4 Avant LPG

  • #2
    1.7 absolute pressure on the UrS dash is 0.7 Bar of “boost”
    Disconnect N75 and see if it’s still only 0.7 Bar. This will tell us if the N75 is doing anything at all.
    The stock spring should only give about 0.4 Bar (can’t remember if you have a stronger spring in the WG).

    S2 Coupe 3B Project


    Ur quattro restoration

    S2 Avant

    Boost is the new rock and roll!
    sigpic

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    • #3
      N75 was replaced by MAC3 solenoid on this car was seeing 1.5/1.6 at a push, and I suspected that might be the culprit, I've fitted my brand new OEM N75 and now ticks over to 1.7.

      I would try ECU out of mine but it's an auto where mine is manual.
      '93 Audi 100 Avant - R.I.P
      '92 Audi UrS4 Avant - SOLD
      '93 Audi UrS4 Avant LPG

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      • #4
        So does boost drop to 0.4 with N75 unplugged?

        Check vac line to ECU and moisture trap is not cracked.
        Check knock sensors are torqued correctly.


        S2 Coupe 3B Project


        Ur quattro restoration

        S2 Avant

        Boost is the new rock and roll!
        sigpic

        Comment


        • #5
          Drops to 1.3.

          vacuum lines are all good, one of the first things I checked and knock sensors torqued to 10nm.

          Comes with Nothelle ECU so isn't standard.
          '93 Audi 100 Avant - R.I.P
          '92 Audi UrS4 Avant - SOLD
          '93 Audi UrS4 Avant LPG

          Comment


          • #6
            Knock sensors should be torqued to 20nm.
            if they are original, I would replace them as a matter of course. Normally they are so degraded you can crumble them in your fingers.
            Panthero Coupé quattro 20vt
            Indigo ABY coupé
            Imola B6 S4 Avant

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            • #7
              Originally posted by Error404 View Post
              Knock sensors should be torqued to 20nm.
              if they are original, I would replace them as a matter of course. Normally they are so degraded you can crumble them in your fingers.
              I believe they've been replaced. Wires were in good condition and intact. I will re-torque them, just to be 100% sure.
              '93 Audi 100 Avant - R.I.P
              '92 Audi UrS4 Avant - SOLD
              '93 Audi UrS4 Avant LPG

              Comment


              • #8
                Does the ECU in an auto car interact with the transmission in some way?
                Just a thought.
                You’ve checked the DV diaphragm? Doesn’t show up in a boost leak test unless you pull the vac line to it.
                Same with the one-way pcv valve, a leaky one doesn’t show unless you disconnect the PCV hose from the maf hose.

                S2 Coupe 3B Project


                Ur quattro restoration

                S2 Avant

                Boost is the new rock and roll!
                sigpic

                Comment


                • #9
                  Originally posted by newsh View Post
                  Does the ECU in an auto car interact with the transmission in some way?
                  Just a thought.
                  You’ve checked the DV diaphragm? Doesn’t show up in a boost leak test unless you pull the vac line to it.
                  Same with the one-way pcv valve, a leaky one doesn’t show unless you disconnect the PCV hose from the maf hose.

                  You think problem with auto box and that's why it's holding back?

                  Checked DV by applying vacuum to the small vacuum hose : all good.

                  PCV valves both replaced and hold vacuum/pressure.

                  '93 Audi 100 Avant - R.I.P
                  '92 Audi UrS4 Avant - SOLD
                  '93 Audi UrS4 Avant LPG

                  Comment


                  • #10
                    Possibly..

                    S2 Coupe 3B Project


                    Ur quattro restoration

                    S2 Avant

                    Boost is the new rock and roll!
                    sigpic

                    Comment


                    • #11
                      Originally posted by Error404 View Post
                      Knock sensors should be torqued to 20nm.

                      If they are original, I would replace them as a matter of course. Normally they are so degraded you can crumble them in your fingers.
                      The torque for the knock sensors is absolutely critical, I'd undo them completely and clean the both the contact surface on the block and sensor with a fine wire brush before reinstalling them.

                      Should you require them I have a set of nearly brand new ones.

                      Otherwise I think John has got you covered with good advice.
                      1989 B3 2.0 3A 80 quattro... Budget 1.8T Project.
                      1992 C4 100 2.8 Avant quattro... Mobile Sitting Room.
                      1995 RS2... MTM K26/7 380 BHP Conversion.
                      1990 Corrado G60... Breaking For Parts.

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                      • #12
                        No luck. Torque to 20nm and still won't see more than 1.6bar. Weird thing is it doesn't misfire just sits at 1.6 bar, so ignition system is good and fuel is getting supplied too.

                        just seems extremely sluggish.
                        '93 Audi 100 Avant - R.I.P
                        '92 Audi UrS4 Avant - SOLD
                        '93 Audi UrS4 Avant LPG

                        Comment


                        • #13
                          Blocked cat? Knackered WG spring?
                          Audi 80 Competition -94 Daily driver

                          www.garaget.org/fish for more pic´s of my cars

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                          • #14
                            I had something similar to what you described and had to much play on the WG valve letting the exaust gases escape and not building boost! it started by not reaching maximum boost till I could only get 4psi and had to have the WG reconditioned and all the boost was back again.
                            Dismantel the top of the WG and check the valve shaft for play lateraly!

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