Subaru knock sensor-related problem.

[colinrmitchell]

My girlfriend's 1999 Subaru Outback Legacy 2.5L threw P0325 - Knock Sensor Malfunction code.

I put a new knock sensor in it. That didn't seem to help at all. I put new plugs in it, and it has new wires for about 8 months now. The plugs seemed to help some. I tried putting 93 in it and that helped a little more.

The car has something like 130k-140k on it. To her knowledge, she is not aware of a timing belt ever being replaced.

So my question is, could a bad timing belt make the engine vibrate enough to make the computer think that the knock sensor is bad? It does seem to vibrate more than I would expect, but it idles alright, about 700rpm.

There is hesitation if the throttle is quickly applied at idle. Also, upon driving, the car seems sluggish until it hits 2500rpm, then it seems to be fine.

When I unplug the battery or erase the code, it comes back on immediately.

Apparently when the knock sensor code is on, the computer retards the timing as some kind of safe mode. Therefore, I am not sure if I am properly diagnosing the timing belt (and I don't really think I know exactly what a bad one would do, anyways). I also do not think that the engine is knocking.

I'm out of ideas and looking to see what could be the culprit? I am sure it's time for a new timing belt anyways, but I wanted to get a few opinions first.

Thanks a lot,
Colin.

 

[colinrmitchell]

I changed the timing belt in the car, and I don't think that really made a difference. The code still pops on almost immediately after clearing it.

I ran some Sea Foam through the brake vacuum line, and wow, did that make a difference! It didn't clear the problem, but it certainly helped!

I am still stuck, though. I threw some fuel-injector cleaner in the gas tank to see if that does anything. I am not sure if this is a fuel problem or an ignition problem or something else.

I am not getting any other codes. The car idles about 700-800rpm after warmed up. It's a little sluggish with just a little throttle. It seems to move pretty good if you give it a lot of throttle. Before the Sea Foam treatment, it stuttered a good bit if you stepped on it, but the Sea Foam helped.

Am I maybe looking at a stuck valved? Bad injectors? I'm looking for any advice!

Thanks,
Colin.

 

[mentalbreakdown00]

I meant to write the other day, but was distracted. Without a scan tool you might not get far on this. The knock sensor uses a crystal and when it is vibrated or squeezed it produces a voltage. The voltage goes to the ecm to tell it to back the timing down. The ecm will deliberately makje it knock for a split second after start up, if it doesn't see it it will set a code. You could have a broken wire between the knock sensor and the ecm, too cold of a plug, or the ecm could be faulty. The latter is the least likely.

 

[colinrmitchell]

Thanks for the ideas.

I ran a new wire from the knock sensor to the ECM. That didn't helped at all.

I probably should have said that the car seems to vibrate more than I recall at idle, which I suppose is another problem causing the knock sensor to emit a voltage which is considered out of range by the ECM.

I have run a vacuum test and a compression test and both turned out okay.

By "too cold of a plug," I assume you are talking about a temperature range? I bought and installed the plugs specified for the engine (NGK) in a Haynes manual, so I'm really hoping I got the right ones, since they were really quite expensive.

 

[mentalbreakdown00]

Sorry meant to hot of a plug. It will not cool enough and cause detonation. You need to check the voltage coming from it at idle, if it has any you may need to find the source of your vibration. With as many miles as you say it has, it may have weak mounts causing it to vibrate.