Knock Sensor - Resistor replacement

The resistor just substitutes the sensor to keep the ECU happy. The lead normally connects to ground through the 560k resistance of the sensor itself. Afterwards, it connects to ground through the 560k resistor ...too easy. Just do it right tho... use solder, ground lug, heat-shrink tubing, etc. If you do a hillbilly "twist-n-tape" job, you'll end up with CEL's.

I've done it on both my Imprezas ('02-2.5 & '00-2.2). The 2.5 knocked just a little on 87 octane with the sensor bypassed, but the 2.2 didn't knock at all.

The thing is, I also cranked the timing all the way forward by adding 47k resistance in series with the IAT sesnsor and run 93 octane in both vehicles now.

Like most engines that have the timing retarded to cut NOX, they really come alive with the timing restored to a power setting. I'm guessing about 6 ft./lbs torque increase, but also a livelier "feel" thing as well.

You've gotta keep an ear out for knock though.

Danny Russell wrote in news: snipped-for-privacy@4ax.com:

Thanks for the response, I have a 99 OBS (2.2L) so hopefully I'll get away w/ still running 87oct. It sounds like the IAT sensor mod you did for additional hp (above spec), is this correct? I'll be more than happy if I can just get normal power. So, hopefully, all I need to do to get there should be the knock sensor replacement.

-Scott

It probably depends somewhat on the individual engine, and local fuel characteristics, but if you keep the injectors, intake valves and combustion chamber clean, it'll help a lot.

Apparently your ECU is entering into the limp mode because of the defective sensor (or connection), which cuts about 10-15 degrees of timing, and REALLY makes it run like dog crap (below 4250 RPM anyway, above that the advance returns).

There's an additional 5-6 degrees or so available via the AIT sensor (+ premium fuel) trick.

Danny Russell wrote in news: snipped-for-privacy@4ax.com:

Actually, mine runs like dog crap thru-out the rev range. It's a manual, so I have the option of keeping the revs high if I want, but that doesn't seem to aid my cause any.

Stupid question. Why don't you just not get a new knock sensor? It's 60-70$ and 15-20 minutes to install...

"Guest" wrote in news:176dnSwU snipped-for-privacy@comcast.com:

Because the resistor job will probably only cost a buck or two. And as much problems as I've read about the Subaru Knock Sensor, it seems like a crap-shoot wether a new knock sensor will work properly or unnecessarily retard my timing too. The cheap resistor should resolve the problem. Mostly it's the buck or two part.. what do I have to lose? If I go w/ the resistor and for whatever reason I end up having to buy a new knock sensor anyway.. what did I lose? A buck or two.

-Scott

Danny Russell wrote in news: snipped-for-privacy@4ax.com:

I'm seeing anywhere from 1/8W 560K OHM resistors to 2W 560K OHM resistors. What wattage should I be looking for?

You can't go wrong by using a larger wattage...a 2W resistor is physically bigger but electrically identical.

-John O

If there were 12V across it 12V^2/560K is only 257 micro watts.

-rick-

Hello Scott,

Did you try the resistor replacement? How did you get access to the knock sensor connector?

Please be carefull when performing knock sensor modifications. Many of the subaru sensors and just too damn sensitive. Adding resistors and such can completely defeat any sort of knock protection. However, adding another washer or gasket made of a soft material (like a real thin piece of rubber) at the base of the sensor will help lower it's sensitivity but still give you some knock protection. However, this does not gaurantee good results. Ask yourslef if there is any other reason the car might be knocking first. My assumption is that you are running 87 octane. This is understandable due to the increase in gas prices. however, running the next higher grade in gas doesn't really affect the pocket book much. The average consumer will spend about 13-20 dollars more a month on gas by using the next higher grade. That's nothing compared to the cost of a new engine because you eliminated knock protection.

It is my experience that these engines LOVE 89 octane when naturally aspirated. and 91 or higher when turbo charged.

Please give better gas a chance before you risk something expensive.

-Dominic Acia

I?m in the same boat as the original poster...A few weeks ago, my 98 Outback?s thermostat blew and had to be replaced. A few days after I picked up the car from the mechanic, the CEL came on. A quick trip back to the mechanic showed that it was a bad knock sensor. The mechanic said the car?s driveable, so I?ve been making short trips with it. The weird thing is that sometimes the CEL doesn?t come on, but there?s no rhyme or reason to when it goes off. (For example, I parked the car and started it again a few minutes later and no light. Another time, the light was on, I turned on the A/C, and the light went off. Having said that, it?s on the overwhelming majority of the time.)

I?d like to change the flipping sensor just to be safe, but I can?t find one online and the local parts store wants $165 for one. Also, I?m not the greatest with cars, but this sounds like a simple fix. Is there a manual that anyone can recommend? Anything online I can find that will show me where the knock sensor is?

Thanks in advance for any help.

replying to Nick Lamendola, VectorSigma wrote: My 01 Outback limited has a slight rod knock at idle and it is setting the knock sensor high input code. would any of the above suggestions work to get the light to go off? like repositioning the sensor? Or using a vibration dampening material between the block and the sensor?

MANY people at both subaruoutback.org and ultimatesubaru.org have good luck using cheap knock sensors from ebay.

remove old one noting which way the cable goes, wire brush the mount location, install new sensor paying attention to the cable direction and don't over-torque it. (anyone know the spec?)