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  • 7A Engine Startup Behavior

    My 1991 Audi Coupe with 20V 7A motor used to start such that the RPM would increase to 1200 and then settle at about 800.

    The problem I need help with is that the car often needs throttle to start if it has been sitting for over 30 minutes. Even if it starts, the RPM doesn't jump to 1200 but just stays at about 800. If I start the car with throttle-assist, turn it off and then restart, it starts right up without throttle-assist, with RPM jumping to 1200 and then back down the 800. If I wait about 30 minutes, the RPM 1200 to 800 again does not occur and the car needs throttle assist.

    The ISV is new and I have adjusted my idle speed/CO to spec. My fuel pump is new and primes well, FPR works, injectors are new. There are no vacuum leaks. There are no codes. My ten measuring blocks are within normal range. The output checks reveal that the ISV functions. Priming the pump a few times does not make a difference. The problem occurs with engine hot or cold.

    What are your thoughts?
    Last edited by cgharibo; 17 January 2020, 02:40.

  • #2
    I've got a 90q 20v. I've had it 14 years and it's never needed throttle to start. It always starts first turn of the key, hot or cold. The only time I needed throttle was due to a leaking fuel line. I was able to get round this by priming the pump 3 times before starting and it would start as normal. What happens with starting if you prime the pump several times before attempting to start ? Turning on the ignition should run the fuel pump for 2-3 seconds. It sounds like a fuel pressure loss issue. Are you still running Hitachi injectors ?
    Mike

    http://www.s2-audi.co.uk

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    • #3
      Thank you for your input. I've tried priming the fuel pump a few times which has not made a difference. I am running the 034 injector modification.

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      • #4
        /\ This is your problem. 034 injectors are not a perfect match for the OEM Hitachis = poor fuelling on low opening.
        Panthero Coupé quattro 20vt
        Indigo ABY coupé
        Imola B6 S4 Avant

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        • #5
          I had a similar problem with mine. Turned out to be bad wiring connector on throttle body.

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          • #6
            This is an intermittent problem, so this may be very well be it. Which connector on the throttle body? Can this startup behavior be due to MFTS or the throttle potentiometer or the idle switch?

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            • #7
              Originally posted by Error404 View Post
              /\ This is your problem. 034 injectors are not a perfect match for the OEM Hitachis = poor fuelling on low opening.
              Alex : What would you recommend in their place?
              Peter S

              1990 ErsatzS2 - track toy
              1991 Coupe Quattro
              1991 Coupe Quattro
              1995 S6 Sedan
              1995 S6 Wagon

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              • #8
                Refurbish or replace originals, or recalibrate the ECU correctly to suit the different injectors
                Panthero Coupé quattro 20vt
                Indigo ABY coupé
                Imola B6 S4 Avant

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                • #9
                  Originally posted by Error404 View Post
                  Refurbish or replace originals, or recalibrate the ECU correctly to suit the different injectors
                  the original injectors were trash when they came out

                  the red bosch will make the car run a bit rich, but nothing major.

                  What originally Patrick Carlie was using, the grey one, was perfect.


                  https://www.audiworld.com/tech/content_eng83.html
                  Last edited by varia; 18 January 2020, 00:19.
                  sigpic

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                  • #10
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                    sigpic

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                    • #11
                      Originally posted by Error404 View Post
                      Refurbish or replace originals, or recalibrate the ECU correctly to suit the different injectors
                      How does one go about recalibrating the stock ECU?

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                      • #12
                        Originally posted by varia View Post

                        the original injectors were trash when they came out

                        the red bosch will make the car run a bit rich, but nothing major.

                        What originally Patrick Carlie was using, the grey one, was perfect.


                        https://www.audiworld.com/tech/content_eng83.html
                        Is the grey injector still available?

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                        • #13
                          Originally posted by cgharibo View Post

                          Is the grey injector still available?
                          Are the grey injectors Bosch "0280155931"?

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                          • #14
                            I think it was the idle switch. 2 pin black connector on top of the throttle body, mine was the later 4 plug ecu model.

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                            • #15
                              Most of the plastic plug bodies on mine have been replaced. New plug bodies, and connectors made a big difference on mine and when you saw how crumbled the throttle position sensor plug was - its not too difficult to see how it was making and breaking continuity. 29years of heat had destroyed them.

                              Worth doing to rule it out.

                              Recalibration the ecu is possible for everything other than wide open throttle. I've been there recently and the tuner couldn't access the WOT map. It's just not accessible but, to be fair how much time do you spend at WOT? I'm happy that mine is better more of the time if not quite acheiving it's maximum.

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