acceleration hesitation

Posts specific to the 2.5 litre turbo engine

hesitation

Postby jp928 » Wed Jan 09, 2008 8:23 am

Cant (yet) speak for a GT, but in my OB the hesitation showed up in low gears as almost no power if under 2k rpm - it would slowly accelerate until it reached 2k, then pull away as normal. Initially I was running unleaded, dealer blamed my driving style, service manager drove it even more conservatively that I do and said it should behave ok in that style. Once when I had the problem it cleared within a couple of 100m after adding the fuel treatment stuff to a full tank. I changed to 98oct and it went away for a year, returned briefly, I fitted the rubber washer under the knock sensor, problem went away, removed the washer after a few months, remained OK. It seemed to come in after several days of stop-start heavy traffic coming into city. You might blame somebody's driving if they change up a gear too early, but when it occurs taking off in first...
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Postby coyote » Wed Jan 09, 2008 8:49 am

Whilst it's merely a bit foolish to disable the knock sensor of an NA car, it would be an absolutely moronic thing to do in a turbo with an adaptive ecu unless you are planning to sell it VERY soon.
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hesitation

Postby jp928 » Sun Jan 13, 2008 5:08 pm

I take your point, but the intention was to attenuate the sensor signal, not disable it altogether. Do you think that its a coincidence that softening the knock signal fixed my problem (and many in the US according to the web), or there is a connection that might indicate over activity from the sensor, or at least over-reaction to its signal? To me the quick change in behaviour said the two were connected. The only definitive test would be to log all the signals when the problem occurs, and see if the knock signal is high, or is it something else, but if thats been done, I havent seen anything about it.

If I do get to order the GT-B wagon 6mt, I intend to ask the dealer (before ordering) what service will tell me if I report the hesitation problem, and if I dont get a straight answer , I may just walk away and look elsewhere, reluctantly.

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Postby coyote » Sun Jan 13, 2008 8:05 pm

JP, I also take your point and agree with much of it.

Where we differ is that I would not assume an active knock sensor is a sign of a faulty sensor. If you were down a coal mine and canaries are dropping dead, do you assume the canaries are faulty?

Subaru seem to produce a very dodgey one size fits no-one tune for world markets that relies on the knock sensor to prevent buggering engines. Excellent examples of just how bad some are would be the B4 Liberty and V5 STi.

I suspect the problem is the tune which is very conservative in some areas and aggressive in others - hence causing the knock sensor to do it's job. Unfortunately this is only a band aid as many B4 and STi found out.

As for the Subaru dealer and Subaru Aust in general, they will tell you there are no hesitation issues. In fact Subaru Aust seem to believe their cars are perfect and it's only their customers who can be improved.
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hesitation

Postby jp928 » Mon Jan 14, 2008 10:40 am

Coyote,
Nearly on the same wavelength. If the hesitation comes in without changing the fuel (currently BP ultimate for 2.5 yrs, but does BP's formulation drift?) or driving style (??how to assess?), and goes away by adding the washer to sensor mount, surely there is a connection? Or is the ECU like Windows, ok one day, BSOD the next? Is something else vibrating and fooling the Knock sensor? Are there some other variables I am not aware of?
It looks like some cars are immune to this, others are intermittent - is that your impression? Similar to the oil consumption problem. Is there an ignition learning process for the Turbos, as in the NA cars - 5 runs of 40-65k, 3rd gear, WOT?

Whats been your experience so far with yours? Any comments on the audio - does it have multi-disc random capability, hows the MP3 output quality? I put a JDM facia with double din cavity in my OB and a JVC DVD reading HU, and the audio output from MP3 is much better than the std unit there. I am going to get an Aux in fitted, but thats just a band aid really IMHO.
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Postby coyote » Mon Jan 14, 2008 12:03 pm

As above, I suspect your car is still pinging .. the ecu just won't know about it until it's far more severe now.

Sorry, but the only comment I can make about the audio is that it works.
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Postby Ric » Mon Jan 14, 2008 12:47 pm

If it's a pinging problem, you could try adding a bottle of octane booster to the tank (e.g. Nulon Pro strength Octane Booster)
or a few tank fulls of Shell VP Racing (100 octane, 5% ethanol)
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