Tranny shifting funny? Maybe Knock sensor. (ed.)

[uniberp]

(ED UBrp> ALL WRONG. It was knock sensor, I am pretty sure. See bottom of thread - 3rd Uniberp post from 7/9/07..)

 

The Legato at 145k got new liveliness when I installed an O2 sensor, an off-the-shelf Walker part $75.

 

After all the worry about adjusting the tranny, having it flushed, etc, then reading the thread about "How many miles on your EAT?" and all the fuss about OEM O2 sensors, etc., No CEL light, no OBD2 codes, just passed Illinois mandatory emissions testing, nothing to directly indicate any problem. (Emissions test was conducted it idle, through the OBD2 connector only.)

 

I decided to make a bet on it. (ed. Lost that bet)

 

It fixed all the balky shifting, the hesitation, the apparent 'bind-up'. The car runs 100% better.

 

I mentioned it to a guy I work with who was a tank mechanic. He said "Yep, those are maintenance items. Should be changed every 50k miles."

 

I don't even mind having bought 2 wrong tools to do the job. A normal 02 sensor socket will not fit, and once I got my 22 box-end in there blindly, working from behind the front wheel, and die-grinded the rusted bolts off the catalytic convertor heat shield, it slipped below the bolt faces and felt loose, so I though it must be 21, and bought a bee-eeeutiful 19-21 combo flare nut wrench from Sears (my reward for a job done myself). Of course that didn't fit, so once I undid the wiring and fished the pigtail through the wrench and worked at it from the front, the sensor loosened easily and was replaced in 5 minutes.

 

The correct tool seems to be the offset short sensor socket, which probably allows you to NOT remove the heat shield.

 

But then, you wouldnt have 6 (5?) shiny new stainless nuts and bolts holding your heatshield on, like I do on mine.

 

So, my new mission and standard response to all driveability problems will be "Change your O2 sensor." just like my standard response to handling questions is "Change your ball joints."

 

 

mpergielelmhurstil97legato99foretier

[ron917]

The TCU uses information from many of the same sensors as the ECU. I don't know if it uses the O2 sensor directly, but the Engine Control and Transmission Conrol units talk to each other. If one has incorrect input, the other will also have incorrect input.

 

But then, you wouldnt have 6 (5?) shiny new stainless nuts and bolts holding your heatshield on, like I do on mine.

 

I hope you put antisieze on them. Stainless steel nuts and bolts don't corrode, but they gall badly even under pressure of normal tightening. They end pretty much welded together, and you'll have to cut/grind/break them off anyway.

[idosubaru]

really? an O2 sensor made a difference in shifting? anyone know any more about this?

[uniberp]

really? an O2 sensor made a difference in shifting? anyone know any more about this?

It's not my imagination. It is definitely shifting better, that 1-2 shift happens correctly with no bang or flare (although I haven't tried it in very cold weather), and there is no lagging flat spot at 2300 rpm. It's hits 4th earlier and stays there unless I WANT it to downshift.

 

The only problem is now I expect my gas mileage will suffer, because I have a much snappier car, and the confidence to move more aggressively in traffic.

 

And yes, yes, antisieze. If it came in 5 gallon buckets I'd still always be out of it.

[uniberp]

All wrong. I am an amateur idiot. Explanation follows.

 

The bogging returned after a few days.

 

Here's my hypothesis and experiment. The battery was disconnected while the o2 sensor was being replaced. This reset the ECM to default, ignoring the knock sensor input. After a few days, hot weather, AC on, knock sensor resignals and ECM goes into ignition retard mode (how appropriate, same mode as where I spend lots of time myself, evidently).

 

I bypassed the knock sensor with a 470k ohm resistor (nearest single resistor to recommended 510k ohm I could find. I will review my resistors in series lessons.). Bogging down at 2000-2500 ceased. Car ran better on the way back from the RadioShack at lunch.

 

I found several threads that referenced a Subaru TSB, and something about an "enhanced" ECM. I ordered a new knock sensor, because I LOVE throwing hardware at the problem, but I think this might REALLY be it THIS TIME.

 

Bottom of this thread:

http://www.ultimatesubaru.org/forum/showthread.php?t=880

 

I apologize, this is the first OBDII car I have really been able to tinker with. And tinker I do.