98 ej22 in a Legacy L. ~141k I'm pretty stumped at this point and I appologize for a long post - bare with me here:
After an oil change I start the engine with the knock sensor disconnected. I
then reset the ECU or clear the code. Don't ask me why - it prevents
the bogging issue - it works for me.
After the latest oil change at 140k (Castrol 10w-40, FRAM filter), however, I have
been getting the typical knock sensor bogging issue even after the
tribal oil change dance. I moved the knock sensor to the location of a factory ground point (on bracket above starter), reset the ECU and drove for about 100 miles. Knocking? Yes. Hesitation, bogging BS? No.
Corrosion was apparent on the mating surfaces so I sanded them back to clean metal. I then tried the old knock sensor in the factory location, reset ECU and got no joy.
I do observe the ~15mile learning cycle by the ECU before it begins to
bog. It is at this point I was confident a new knock sensor would fix
my woes. I purchased a new Knock Sensor from Autozone and installed in
correct location with about 15 ft-lbs making sure to orient the wire
lead so that it was clear of block protrusions. Reset the ECU and got
no joy. Now I started to suspect a bad connection so I cut the wire and
hardwired the old knock sensor in sans connector. That resulted in no
change of symptoms (see note 1 below).
Now I was becoming befuddled and a bit ticked off.
I can change the performance of the car by relocating the knock sensor
but a new one won't fix the problem. I figured I didn't need a new
knock sensor and, at this point, I started to march down the path of "Gee, maybe there's too much knock!" so I returned the new KS to Autozone.
I drained/refilled and burped (to death) cooling system and installed a new thermostat (the bigger OEM type) and a new rad cap. Operates right around 180-190F according to OBDII data so it is not running hot.
Then I went after the ignition system a bit: I installed $40 NGK wires and NGK Irridium plugs gapped to a tight 40 thou. I also installed 500 pounds of copper all over the place to enhance grounding. I cleaned
the mating surfaces of the igniter and it's mounting plate, although
the igniter is currently sitting on two ring terminals - one as a spacer
only - the other with a lead directly to a ground point on same sheet
metal platform igniter is mounted to. The coils are about 25k miles old and I have an older set which I have swapped out with no change in symptoms. The coil contacts are clean and I use dielectric grease on the plug wire boots.
Then I filled up with high octane gas and reset the ECU.
With the original KS installed in factory location I still got the
bogging issue. When I move the KS to my off-the-block location the
bogging goes away and there's no audible knock with high octane gas. So, at least I know that high octane gas really has a higher octane.
all this I went to the junkyard to source an OEM connector and soldered
it in. There is a short section where the sheilding is soldered
together but the rest is completely sheilded - see note 1 below. I then
went back to Autozone to buy a new knock sensor. I did this with the
hope that I would get another knock sensor (not the one I returned) but I
got the same one. I'll ask and see if I can try another next time I'm
I purchased a BAFX Bluetooth OBDII
adapter (cool tool) and tried to read engine parameters with Torque
Lite. All I got was engine temp and load so an actual analysis of
engine parameters was a dead end there. (If I buy Torque PRO will it
give more engine data or is my car just too old-school?)
this point I'm thoroughly stumped. I will check the main harness
connections but I don't expect anything to come of it. I saw some other
threads on USMB with good info but it seems the threads just died
without any real resolution - here, here, and here.
I can't imagine it is anything other than knock sensor related. My
next steps are to check the car's recall history and see if I can get a
hold of a second new knock sensor to test the infant mortality theory.
If a third knock sensor makes no change perhaps the ECU is to blame.
All pointers/tips/ideas are welcome and appreciated!
- I have a degree in Electrical Engineering and can surmise
that the real need for the sheilding on the knock sensor wire is when
ignition parts begin to leak their current i.e. a leaky spark plug cable
that is jumping to metal on the engine somewhere rather than fully to
the plug. I can't imagine that there is any other source of electrical
interference in the engine bay that could induce electric current in the
wire - mine was a short, unsheilded piece which, I believe, means there has to be a
LOT of unshielded current flowing somewhere else before any induction
will take place in the short unsheilded wire to the knock sensor.