my89xj

Noticed this the other day. Is it a sensor, if so how important is I've been driving the xj a lot and it looks like its been broken awhile.

grsmnky1

I believe thats your knock sensor. It is a computer sensor that you should probrably replace.

my89xj

Yea, Im trying to find a write up on how to do it. Not sure if its simple or not.

DFlintstone

X2, Looks like the knock sensor. Should be no problem, just unscrew it. It senses vibration from the block from pre-detonation, and tells the ECU to retard the timing.

One poster suggested us renix owners with those might get better economy by running premium because of that. Once I'm sure I have no other issues I'll try it.

(the idea being if more spark advance is allowed due to no pinging, that the $/mile might improve)

my89xj

ok so the knock sensor, is another name for the cps? how is it running without it?

DFlintstone

No, the crank position sensor is back on the bell housing. I juess the ECU will gradually increase spark timing in increments until the knock sensor tells it to "knock it off" (something like that). I'm curious. When your engine is hot, and you really get your foot into it, do you hear any pinging from the engine? (especially at lower RPM)

my89xj

no i dont hear any noise.

DFlintstone

Huh. Well I don't know the details. I thought maybe it should, ("ping", or knock). I don't suppose you are running premium. I wonder if you might have some other issues going on. It will run in "open loop" using just a few sensors until it warms up, then go to "closed loop" and use more of them....I ran around forever with my 02 sensor not working at all, and didn't know it. I got decent mileage flying down the freeway, but it just sucked running around. I guess it was dumping a bunch of fuel if I was using it or not. After I fixed it the heat started coming on hotter faster, and the idle stopped cycleing every 20 0r 30 seconds. Mileage came up, but it's still down around 16 running around. All that fuel was making it run too cool, usually.

Anyway, Cruiser54 is one renix expert here. If you click on my signature there is a bunch of stuff there he wrote for us.

Well I checked. it DOES use the knock sensor in open loop....but shouldn't knock anyway when its so cool, I don't think.

my89xj

Knocks when idle

DFlintstone

Mine is absolutely quiet when idle. (except for the mice).

my89xj

This is what the knock sensor plugs onto and its destroyed, will a new sensor come with one?

my89xj

Ok the sensor is replaced, it isles smoother but that's about it

jakbob

thats all the knock sensor does. regulates pre-ignition. when it detects a knock, it advances the timing.

DFlintstone

The other way Jakbob! Retarding the timing helps pre ignition.

Thanks for getting back my89, we appreciate that. Yea that plug looks like a hassle. I was just down there and noticed it's got the spring clip like on the injectors. Actually, now I remember seeing that in an injector swap thread...had I remembered that before...that might have helped!

my89xj

It was probably the easiest thing to replace on my xj ever