Knock Knock

[yblocker]

New to me 2000 Outback 2.5 4EAT. 166,000 miles. Starts easy, lots of power, great idle.
Threw a P0325 knock sensor code while driving up a moderate grade at 35 mph. The knock sensor had a crack in the plastic housing. It ohmed out OK, but I went ahead and replaced it with an OEM sensor.

Drove it up the same hill today, as the first test drive with the new knock sensor. CEL again; this time it threw a P0113 intake air temp code. It was pinging noticeably when the CEL lit.

So I find this to be a puzzle. With the new knock sensor, I would think that if it hears pinging, then the timing should dial back, and the detonation would be reduced. The knock sensor is installed in the correct orientation to 17 ft/lbs. The sensor wire from the ECU has 4 volts. That all seems right.

What triggers the P0113 code? I filled the tank with Chevron Supreme and a bottle of Techron, and ran the same hill again after clearing the P0113. It didn't ping and did not code on me. Maybe it was bad gas that came with the car? Should I throw an air temp sensor at it?

[3Pin]

https://www.700r4transmissionhq.com/p0113-subaru-outback/

 

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[jonathan909]

21 hours ago, yblocker said:

The knock sensor had a crack in the plastic housing. It ohmed out OK, but I went ahead and replaced it with an OEM sensor.

I don't have an answer to your question, but would like to point out that taking a resistance measurement of ("ohming out") the knock sensor will give you a meaningless reading.  You cannot test it this way, because it's a piezoelectric transducer.  It's like your BBQ lighter - a crystal that, when physically shocked, generates a voltage.  You might as well check the temperature of your oven with a bathroom scale.

Edited September 14, 2021 by jonathan909

[yblocker]

Thanks to both of you.  The running a lean AF mixture does seem to fit the symptom of detonation.  I noticed that the IAT sensor schmekle was pretty oily which might cause it to respond incorrectly and lean things out. I cleaned it with some of that CRC MAF cleaner spray.  I also pulled the PCV valve and it was pretty gummed up which may be a cause of oil in the intake.  I cleaned it out with some carb cleaner until it freed up and rattled easy.

As far as testing the resistance of the knock sensor goes, I could have sworn I saw a spec that stated that the resisitance should exceed 50.000 ohms.  Either way, I like the bathroom scale comparison. Funny!

I'll keep driving it and see how it does. Thanks again.

[jonathan909]

Sure, the >50K check will tell you at a glance whether it (or the cable) has suffered a catastrophic failure i.e. short, but that's about all.  The problem is that it can also mean that the device/wiring has opened up, so it remains a pretty much meaningless test.

Looking back at your original posting, though, I realize that it could have been read as "zero K" or "okay".

Edited September 13, 2021 by jonathan909

[1 Lucky Texan]

How old is the fuel? maybe try some HEET in case there's water in the fuel?

[yblocker]

Yeah- maybe "bad gas"... Although that's pretty rare in my experience. But that's why I put the expensive stuff in there with someTechron.  Maybe the injectors will like it.

[1 Lucky Texan]

slipped timing belt might be a possibility. Bring the sprockets to their marks and do a tooth count (find your engine's tooth count online) might be off 1 tooth somewhere.