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having a hesitation issue on sharp throttle movements - could it be the ECU?

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  • having a hesitation issue on sharp throttle movements - could it be the ECU?

    scenario: car warms up, when i stab the throttle sharply (as in a rev match downshift, or just getting revs up to take off from a stop), it responds, hesitates (will not drop revs), and responds again (almost as if i am blipping the throttle twice).

    car specs: speed density (no MAF), relayed 044 fuel pump with less than 20k, 550cc injectors with less than 20k miles on them, new fuel filter with less than 10k miles on it

    before you ask: I have done the following

    - ISV/IAC
    - TPS
    - vacuum leak test
    - spark plugs
    - replaced all coil packs (2.0T)
    - fuel filter, air filter

    many have been suggesting that i replace the ECU. is there anything else i should try?

  • #2
    Have you got a vagcom that you can use to do some datalogging to try and pin down what is happening and what the ECU is seeing? It may help narrow down if it is a sensor or ECU as it may be the wiring to one of the sensors that is an issue rather than the sensor itself.

    Have you also tried checking out the wiring from sensors to ECU for any breaks or bad connections?
    Greg

    S2Forum.com Administrator & Webmaster

    '93 Coupe with a few tweeks

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    • #3
      I guess you have checked for air leak's this could hold up your rpm and it's a easy thing to check for. Does the throttle body snap closed quickly? Maybe gummed up ?. Just a couple of easy things to look at. Hopefully it's not too painful and you find it quickly. Good luck

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      • #4
        Greg_S : i do not have access to a VAGcom unfortunately, my only resort as far as consulting goes is taking it to my tuner who lives 6 hours away

        LSG : i have checked for air leaks! nothing seems like it could be getting out as far as i can see, which sucks as that is what i was expecting it to be. will clean the TB, and see if that helps my case

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        • #5
          How was the conversion to speed density done? Is it PRJ Mod?

          S2 Coupe 3B Project


          Ur quattro restoration

          S2 Avant

          Boost is the new rock and roll!
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          • #6
            Checking for air leaks is not good enough. You need to pressurise the whole inlet tract from the MAF hose to about 1 bar, it should hold pressure or at least leak down slowly.

            In any case to run SD it has to have been tuned so it could just mean you need some adjustments to the mapping. Do you know who tuned it? Is it still Motronic ?

            S2 Coupe 3B Project


            Ur quattro restoration

            S2 Avant

            Boost is the new rock and roll!
            sigpic

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            • #7
              newsh that’s what was done, it was smoke tested and the system was pressurized to test for any possible leaks

              the car is tuned by marc swanson from efiexpress, i’ve been trying to get in touch with him regarding this but he’s a busy guy

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              • #8
                Did the car ever drive good with this setup?

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                • #9
                  Acki yup, it drove great when i had it initially. this is a problem that has developed, not one that was always there

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                  • #10
                    Speed density uses MAP sensor and IAT against RPM to measure air entering the engine and therefore calculate fuelling, so check your IAT is connected and your vac line to the ECU is good
                    Also pull the vac line to your Diverter valve and suck on it to make sure the diaphragm is intact.
                    Make sure the temp sender on the back of the head is connected and working. This is the one the ECU uses for warm up enrichment.

                    If you have a windows laptop and the car is still running Motronic, you can use the Vagcom lite version with an eBay cable for a few £.

                    S2 Coupe 3B Project


                    Ur quattro restoration

                    S2 Avant

                    Boost is the new rock and roll!
                    sigpic

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                    • #11
                      newsh the diverter was replaced with a forge 007, i have replaced the coolant sensor at the back of the head with no change in the car’s behavior.

                      i’m done playing parts darts with my car, i will be taking it to marc swanson in one week to diagnose the issue

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                      • #12
                        Would be great if you could post up the eventual diagnosis and fix - could help others in the future...

                        Good luck with getting it fixed asap
                        Honda CBR 1100XX Blackbird Turbo....undergoing major changes.....
                        S2 Coupe... bit easier off the line...
                        '03 ZX12-R daily hack.... lots of nice bolt ons...

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                        • #13
                          hey guys, update:

                          i got the car retuned and it seems to have alleviated the problem mostly - however, it still isn’t completely gone. i’m guessing this is something i’m stuck with until i rebuild the motor and have to dive through every sensor, connector and ground. it doesn’t greatly affect drivability (downshifting, blipping to get rolling) as it used to, and i have adjusted my driving style to blip in a fashion that the car likes (lol).

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