Hessitation in Late Model Subarus

[Bruce Plecan]

>From reading his post and URL, it seems that the ecm is having it's knock
detection system triggered.  There was no mention of any audible, knocking
type sounds.  SOA has a cure that involves replacing the ecm.
   The assumption on their (original poster's) part is that this is a false
signal.  In a prior post I mentioned some things to check.  Then work can
begin at looking at things, Least that's the way I'd do it.  GM has had
problems for a long time with trace ping, and tip in ping, that can be
non-audible, but triggering the KS..
  Just putting a pot in the system to turn down the amplitude, is a down and
dirty thing to do, without examining what the true problem is in my book.
   Yes a knock detector circuit probably could be just a 741, and $1 worth
of other stuff, but that is just a threshold noise detector.   Which would
probably be fine for many ecms.  But, I would tend to think a OBDII box is
smarter than those.
Meaning when it goes thru it's self diagnostics, and listens for a response,
when doing the ESC test.

> -> OK, just for giggles, how do you tell a bad A/C compressor bearing
> -> that radiates a frequency of 25 Hz,  from a knock "noise" of 25 Hz?.
> -> (Feel, free to change to any freg of noise)

>  Amplitude.

?. A stethoscope, and microphone?.   Or are you looking at this as an
audible knock?.
What a dual trace scope, and one lead to the KS trigger line, and one to
another piezio electric device, and compare each bearings noise, to find a
similiar trace?.

>  Even my wife can recognize it when the engine pings.  Real detonation
> can be recognized by drivers in nearby cars.

OK, if the ecm has a limit for the amount of retard and that doesn't take
care of the detonation, then it will be audible.  But, if the knock limit is
7 degrees and 5 degrees retard takes care of it, performance will be down,
and you won't hear any detonation.
  If it is false knock it will run the KS right up to the 7 degree max, and
just ruin performance..

>  You have to decide what you're looking for here.

And the long term effects of what you do.

>If you're trying to
> listen through all the rumble to find erratic igntion events so you can
> fiddle with the advance or mixture, you're trying to do something even
> most OEMs don't try to do.

 My interuption of the 99 vette ecm is that it will do individual cylinder
knock/miss detection, and try to cure it with mix/timing changes.  In one
shop manual they mention that, but in the training manual there is no
mention, but that is from a yet to be updated manual.
Bruce

> If all you want is to know when the engine
> is in danger of damage, almost anything will do - I have a Carter EKE
> box (add on knock eliminator, sold for $75 back in the '80s) that works
> just fine, and it's just a handful of discrete analog components.
 ==dave.williams at chaos.lrk.ar.us======================================