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Engine Fighting Gearbox SM4 Tune or it feels like it

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  • Engine Fighting Gearbox SM4 Tune or it feels like it

    Got a tune on a 2000 Subaru Forester running an EJ25 with a AVO 450 turbo (18psi nice flat boost curve) and appropriate supporting mods(injectors, exhaust, inner mechanical workings etc). This is all coupled into an Albins straight cut 5 speed gear box.
    When I bought into this car I knew it needed a little bit of tweaking not a complete EVERYTHING was wrong tune, learnt a lot about tuners, and got it tuned, power is great fuel economy is great (well at least now after getting it tuned). As the nerves wear off and I get braver I've noticed a niggle, I don't know if it is mechanical or tune related and hoping it is a glaring obvious setting in the attached cal file.
    Basically if I'm just driving around town, low throttle position around the 3kRPM mark, I will get an oscillation of RPM starting out at small (e.g. 10ishRPM), but slowly increasing to to a rather violent jerking motion of the car. More or Less throttle gets it away from this effect and settles it down, and as such it has forced an interesting change of driving style. I would like to work out what is going on but I'm really not a fan of my local agents as they blew me off the first time over the build.
    I've tried to capture it with logging both manually and autologging and can't get a good capture of this effect, but I can assure you it is quite violent if left to grow.

    Thanks in advance for ANY assistance you can offer.
    Attached Files

  • #2
    are you saying when you are driving at a steady speed/RPM the car starts jerking?

    when it happens, what are your:

    1. throttle position
    2. timing
    3. AFR
    4. load


    • #3
      Yes, steady throttle position, generally <10% however trying to get a clean log of the event is almost impossible as it is an older ecu and appears to have limited onboard memory and the laptop on the passenger seat makes it hard.

      1. <10%
      2. not sure haven't been able to log/capture the event with laptop.
      3. Excuse the dumbness of my answer, but i'm not sure how I can get that.
      4. again with can't capture it in log, but I suspect it is under very low load conditions. Road wise it is either flat or low grade decline.

      Additional information, some highway cruising was done yesterday and I noticed that it would occur a lot more 2 and 3, however less so in 4th but could not seem to get it to occur in 5th.
      Is there a method to increase the amount of time that it capture for without juggling the laptop in the car?


      • #4
        I suspect you have a bad tune, wrong timing, or too lean AFR (air fuel ratio) at that point
        I would try to find a tuner locally and have him take a look


        • #5
          You can set the laptop logger to work above 2000 rpm or does the laptop not have enough battery life for a drive.


          • #6
            this is exactly what i experienced with my evo i believe ,when cam settings was to aggressive. it disappeared when i detuned the cams to a more street like overlap. It only appears with low tps values and if you don't stop it with the clutch it feels like is going to damage something. Is it same as that ?


            • #7
              Originally posted by krbtrading View Post
              this is exactly what i experienced with my evo i believe ,when cam settings was to aggressive. it disappeared when i detuned the cams to a more street like overlap. It only appears with low tps values and if you don't stop it with the clutch it feels like is going to damage something. Is it same as that ?
              also when tuning cams for city, I noticed it is crucial to make very smooth stepping between the cells
              however OP mentioned MY00 EJ25 Forester, so I assumed the car was not equipped with AVCS


              • #8
                my mistake ,if stock non adjustable cams should not be an issue


                • #9
                  Hmm I may have to head back to the tuner who did the current setup...
                  Sadly I've bought into someone else's project for what is in this setup.

                  I've taken the laptop with on drives, but I have been unable to replicate the fault condition when actively logging/looking for it.
                  It was mentioned an EVO that would need clutch intervention, I've also found either more or less throttle will get it immediately out of this rocking motion.

                  I've also seen other videos of people driving Dog Boxes on Subaru's in a street capacity, so it may be the case as mentioned that my tune may be too track for some occasional street driving....

                  The only other thought I've had (sadly I don't know too many driving dog boxes around to learn from) that it could be gear spacing/tooth spacing since it is a straight cut setup.

                  I shall chase the original tuner for it, but will also attempt to carry the laptop on all times to log it playing silly buggers.

                  FYI:- the car was tuned at PITS in Queensland (Australia), which eliminated ALL the issues purchased with the car (200kms to a tank and lean conditions). And I haven't changed anything since the tune. Believe his tuning methods involved turning off ALL boost then tuning it to run well, then tuning it again as boost is enabled at the points (hence new tune is 18psi now the original)
                  Last edited by Bevan; September 18th, 2014, 12:18 PM. Reason: more information


                  • #10

                    Are you comfortable with the logging parameters Ian illustrated? This will allow you to use the SM4 ECU to manage the logging tasks while being triggered only under specific parameters and/or conditions which you can specify. So the SM4 won't be logging from engine start to engine stop exhausting the limited logging memory available.

                    What may be a great plus is for you to understand or realize some of the specifics associated with the described problem in relation to the engine's operational conditions. So TPS, manifold pressure and engine speed are some of the basics you should keep in mind as logging triggers for the described problem.

                    It sounds like the general idea behind what was being discussed between the posts of krbtrading and hyper relates to the rate of change of the engine's volumetric efficiency in relation to engine speed and TSP values. The model used in the Autronic ECUs allows the calibrations (x and y axis break points) of fuel table not to reflect this in a very pronounced and obvious manner, however, in most common millisecond model based ECUs you can see this reflection in a very transparent manner. Both solutions work rather well, it's just that you have to be mindful of what the model being employed is doing in response to your table values and how the model itself works in relation to your input as well as the input from the engine itself.

                    I sure hope this has shed some light on the task at hand, however, if further assistance is needed to clarify any details of the unattened logging procedure please indicate. Cheers!
                    Damien King
                    Technical Analyst/Engine Management Calibrator
                    Stephen's Automotive Research & Development Engineering


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