Knock sensor weirdness. . .
 

I recently put my 951 back to stock configuration for a pending smog check (put the stock chips back in, CV, got rid of the MBC, etc.) Naturally I have a bunch of mods ready to go on once it passes, but that's a different story. . .

Anyway I noticed after putting everything back together that I was getting "limp home mode" boost limited to 1.2 bar. I did the LED diagnostic on the test port and got blink code 2-2 (knock sensor). Okay, fine. Pulled the knock sensor off yesterday and checked the impedance across it - infinite ohms. "Ah-HAH!" I said. It's supposed to be around 180-330 ohms IIRC. Anyway I suspected a faulty knock sensor and began my search for a replacement.

Here's where it gets weird.

On my way down to the parts store (with knock sensor disconnected and sitting on the seat next to me), I no longer got the "limited boost" brought about by the 2-2 trouble code. Full, normal boost (+/- 1.8 bar). How the eff can a knock sensor with an "infinite" impedance generate a fault code (and limited boost, per the KLR) and having the knock sensor REMOVED (which would also yield infinite impedance at the wire harness) gives me something else?

Bizarre.

Hah! I'm going to try disconnecting mine now, maybe that'll solve my strange, unexplainable issues. For now, I got a clamp on the pressure line from the intercooler intake, and I just keep my eye on the boost gauge. Keeps things interesting and me on my toes. Eventually I'm going to settle for an MBC, just haven't gotten around to it. For the life of me - I've run through the test procedures and everything's happy, no error codes, no leaks, etc, - CV switches at full load, blah blah blah Can't figure the damn thing out. Now if I can just find that person that backed into it the other day and lock them into a room filled with starved rats....

How do I get a copy of the test codes for later diagnostics. I have the shop manuals but never some these.

Ask and ye shall receive. . .

http://members.rennlist.com/951_racerx/

Check under "fault codes". It's actually an excerpt from the factory manuals too, so if you have 'em you should be able to find the information in there also.

i had a knock sensor with a split wire. it was limp mode full time until i got in there (removed the intake, what a hassle) in order to repair the wiring with solder and heat shrink tubing.