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Old 03-21-2006, 10:58 PM   #1
Sean
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Rally Stuff Still getting P0325 CE even after replacing knock sensor. What next?

Cliff's Notes:

North Ursalia and I just spent the evening trying to diagnose a pissed off knock sensor on the Trunkmonkey Pink Impreza (PGT-prepared 1996 Impreza 2.2 L) to no avail. We're still getting a P0325 Knock Sensor 1 Circuit Malfunction (Bank I or Single Sensor) even after replacing the knock sensor. The weird thing is that it doesn't always come on immediately; you have to put 5 to 20 miles on the car before it comes on.

First, what does P0325 actually mean? Continuity between the knock sensor piezo and the block? ECU malfunction? Bad data from the knock sensor (I thought it was either on or off; no data stream). Bad ground?

Now, here's the history for those of you with an attention span:

Tossed a P0136 O2 Sensor Circuit Malfunction (Bank I Sensor 2) shortly before Maine Forest Rally, ignored it after talking it over with the service crew, and ran the event.

With the exception of a few Rallycrosses and Ice Races the car sat in the garage until I had both the front and rear O2 sensors replaced by SubaruProParts.com last Saturday.

Tossed a P0325 (which I'd never seen before) 8 miles from SubaruProParts.com on the way home from having the O2 sensors replaced.

Got home, pulled harnesses, checked for corrosion, plugged everything back in, cleared the code, went for a drive, and it didn't toss the code until 8 miles into the drive. Clear the code, 10 miles later it comes on. Clear the code, 15 miles later it comes on.

Ran a Rallycross on Sunday. The car showed no signs of hesitation or retarding timing before the Rallycross. The car was constantly retarding timing and hesitating on the drive home. The CE light also occasionally flickered; it kept going out for a split second and then coming back on.

This evening North and I pulled the knock sensor which was filthy and corroded, scrubbed the corrosion off the block, and replaced it with a brand-new knock sensor.

Went for a drive, I was up on power, and the car was the best it felt since before Maine Forest.

18 miles in I tossed the P0325 again. No hesitation, no retarding timing, just a P0325.

So what gives? Any ideas? It's not every day that North Ursalia is scratching his head about an Impreza problem.

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Old 03-21-2006, 11:11 PM   #2
SOLUTION
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You could try resetting the ECU one more time just to make sure. No problems with the spark plugs, wires, or coil pack that could be causing problems? Something to do with the oil (low or oil filter)? Just throwing out ideas.
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Old 03-21-2006, 11:58 PM   #3
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batch of bad gas? try seafoaming the engine, or putting some gas treatment in.

(also stupid question) oil change time?
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Old 03-22-2006, 12:30 AM   #4
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One interesting thing to note:

I just cold reset the ECU using the battery cutoff switch and removed and re-torqued the knock sensor to 17.4 per a few posts in the CEL thread and ScoobyMods.com. After doing that and going out for a drive it only took a mile for the CEL to come on. Then clearing the code would cause the CEL to flicker off, immediately throw a code, and come back on. Interestingly, the motor now idles at 2000 RPM.

Plugs and wires were done about a year (7,500ish miles) ago. Oil and oil filter was just changed on Saturday with the O2 sensors. The ECU has been cold reset multiple times using the battery cutoff switch. And gas shouldn't be an issue; I filled up at the same place I always do.

Throw me a frickin' bone here, Mr. Bigglesworth!

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Old 03-22-2006, 12:44 AM   #5
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odd about the idle....the IAC is woring properly, yes?...

the connection to and from the knock sensor are good, right? no loose ends?
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Old 03-22-2006, 12:49 AM   #6
Sean
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Quote:
Originally Posted by rabbitnutz
odd about the idle....the IAC is woring properly, yes?...

the connection to and from the knock sensor are good, right? no loose ends?
Not sure about the IAC but I'll add it to the checklist. This idle problem is new as of about 30 minutes ago after re-torqueing the knock sensor. For loose ends North and I pulled harnesses and plugs, checked for corrosion, and plugged everything back in. I need to track the wiring diagram in the service manual to see exactly which harness the knock sensor is on; there was one harness I couldn't unplug due to cold fingers and sharp edges.

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Old 03-22-2006, 12:52 AM   #7
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stupid stupid suggestion...but try loosening it. just for fun.
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Old 03-22-2006, 03:11 PM   #8
Sean
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Quote:
Originally Posted by rabbitnutz
stupid stupid suggestion...but try loosening it. just for fun.
I'll try that tonight when I install the [yet another] new knock sensor North is giving me just in case the first one was bad.

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Old 03-22-2006, 03:55 PM   #9
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I'll throw in my guess. Check in resistance across the sensor (I have no idea), then check it from the pins at the ECU harness. See if it changes, bump the car around a bit.

If not that, trace the wires all the way back, see if the wires rubbed through anywhere. My guess is you have intermittent grounding out of the sensor that you can't see.
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Old 03-22-2006, 09:02 PM   #10
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So the motor is making no odd noises? Have you checked the timing belt alignment?

Put a stethascope on the block while it's idling and see what you hear.

interresting.
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Old 03-23-2006, 02:09 AM   #11
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Master and Tim, thanks for more things to add to the list. Not enough time to poke at the car this evening but I'll be diving back under the hood again tomorrow night.

Edit: Tim, correct, no odd humanly-audible noises at all. A stethoscope check may reveal something more...

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Old 03-23-2006, 02:50 PM   #12
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Try switching gas grades. Maybe your car needs more octane…
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Old 03-23-2006, 11:57 PM   #13
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It may be solved! Tonight I installed yet another knock sensor (thanks North Ursalia!), replaced the PCV, and filled up with 93 even though the car's been happy on 87 for the past 3 years. Cleared the code and put 35 miles on the rally car. No check engine light so far! I'll put another 70 miles on tomorrow driving to and from work (rally car in Boston commuter traffic w00t) and see if the ECU stays happy!

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Old 05-07-2010, 07:25 PM   #14
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Sean, I know this thread is really old, but I just came across it. My 2000 Impreza is having the same symptoms as your car was. Did the new knock sensor, PCV valve, and 93 octane solve the problems for you?
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Old 05-11-2010, 08:13 PM   #15
Sean
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Quote:
Originally Posted by ray918 View Post
Sean, I know this thread is really old, but I just came across it. My 2000 Impreza is having the same symptoms as your car was. Did the new knock sensor, PCV valve, and 93 octane solve the problems for you?
Yeah, I never updated this thread, did I? Ha. The new PCV valve solved the issue but, if you haven't replaced your knock sensor yet, I'd replace both at the same time. The car has been run on normal low-octane fuel since then with no issues.
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Old 04-16-2011, 09:06 PM   #16
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Quote:
Originally Posted by Sean View Post
Yeah, I never updated this thread, did I? Ha. The new PCV valve solved the issue but, if you haven't replaced your knock sensor yet, I'd replace both at the same time. The car has been run on normal low-octane fuel since then with no issues.
I know this is an old post, but would anyone mind explaining how a bad pcv causes pre-igniton, knock?
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Old 04-16-2011, 11:42 PM   #17
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A bad PCV can cause excessive oil consumption and oil has an octane rating of negative 80 bajillion, causing more knock.


Or so I've been told (about the octane, I know a bad PCV will cause excessive consumption).
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Old 04-17-2011, 12:23 AM   #18
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A faulty pcv may allow excessive amounts of oil vapor to enter the intake manifold.
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Old 04-23-2011, 08:50 PM   #19
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Thank you, you guys- appreciate the info.
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Old 02-01-2012, 10:11 PM   #20
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I know, this is an old thread but i have a question. Is the orientation of the knock sensor super important? I know it's supposed to be 60 degrees relative to the back of the motor, what i'm asking is, if its not exactly 60 degrees will it make a big difference? Say 58 or abouts?
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Old 02-02-2012, 04:34 PM   #21
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I have read those threads too but after putting in maybe 50 i have never had a problem so i would say close is good enough. I also had a 98 legacy that would throw a code if I feed it reg it only liked the good stuff.
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Old 02-11-2012, 04:05 PM   #22
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Default check the harness

Keeping a post alive, before changing knock sensor visually inspect harness had 2 fozys with burnt harness approx. one inch past knock sensor connector on the harness side not the sensor side. Presented as a missfire as burn consumed injector wire that runs in same harness. Solder new plice no problems to date.
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