Hessitation in Late Model Subarus

[Programmer]

Gary,

 Knock sensor torque is "extremely" important. Overtorque is going to make
the sensor over "sensitive" to any noises. From your post it sounds like
you've tried the retorque thing--tried mounting with teflon tape ? Another
fix is to isolate the source of the engine noises--ever try a synthetic lube
? Problem with motor mounts ? Driveline noise being translated through to
the knock sensor ?

I'll have to check the TSB list at the shop for their "fix".

Lyndon
IP TECH
LWester at compuserve.com
-----Original Message-----
From: GARY <hobiegary at earthlink.net>
To: EFI DIY mailing list <DIY_EFI at efi332.eng.ohio-state.edu>
Date: Friday, May 07, 1999 7:02 PM
Subject: Hessitation in Late Model Subarus


>Hello,
>
>A lot of people have had a problem with a stuttering acceleration in
>Subarus.  I offered up an hypothesis along with a fix for the problem.
>My hypothesis was first rejected by Subaru of America, then later
>supported in a Technical Service Bulletin.
>
>Rather than go into detail here, I'll supply the URL for my website on
>the matter. When you go there, scroll down for a lot of links.
>http://home.earthlink.net/~hobiegary/hesitation.htm
>
>Well even though Subaru claims to have a fix for the problem via a new
>ECU, I have yet to hear of anyone who could jump through all the
>necessary hoops to get a new ECU *and* find out that the new one
>actually cures the problem.  So I am not holding my breath on that note.
>
>What I am doing however, is planning on an improvement on my primary
>fix.  The ECU is a OBD2 type with EPROM.  It can be "reset," to loose
>stored trouble logs, by disconnecting the battery for about a half
>hour.  I need to electronically dampen or trim or filter (or whatever it
>is called!) the signal from the knock sensor to the ECU.
>
>What is happening is that the ECU is interpreting non detonation noises
>as detonation and reacting accordingly.  This leads to piss-poor
>performance to say the least.  I have gone the mechanical route,
>buffering the signal by padding the mechanical interface between the
>sensor and the engine block.
>
>What I would like to do is simply reduce the sensitivity of the sensor.
>That is what I did mechanically and it seemed to work pretty good.  The
>problem though is that it is a little iffy and esoteric and problematic
>and lacking consistency.  It is not solid state enough to suit me.  I'd
>rather dampen the signal electrically.
>
>I tried hooking up a variable capacitor in parallel with it.  I thought
>that this would let any voltage spikes bleed (partially) to ground and
>lessen the signal strength arriving at the ECU.  I had trouble with this
>method because as soon as I turned the capacitor a certain amount, I'd
>get a trouble code and would have to shut down and restart.  I'll guess
>that the ECU sends a monitor current through the sensor and detects when
>it is not at the proper impedance.  It didn't seem to help either.  I am
>not convinced that I was doing the wrong thing either.  I just could not
>get any positive results.
>
>I also wonder if I rather should be using a variable inductor in series
>with the sensor.  Wouldn't this choke a signal without greatly affecting
>monitor current?  I guess it would depend if the monitor is looking at
>impedance with a/c or looking at resistance with d/c.
>
>Comments?  Any other ways I should consider reducing the amplitude of
>this signal?  What about the ECU, is there anything I can do there to
>help the situation?
>
>I thank you for your attention Fellows and thank you in advance for any
>suggestions.
>
>--
>GARY       mailto:hobiegary at earthlink.net
>