Leo_Koneval

iTrader: (4)

So I've been having this knock sensor CEL for a long time and went through a few KS sensors thinking it was the problem and so today I took out the whole harness and opened up the wire loom to discover that it is pretty messed up there is electrical tape everywhere.

It seems like someone tried to repair the harness before and got it to work or at least they thought it worked but it was extremely ghetto. Like on one side they used masking tape and just twisted the wires together and the other electrical tape. And don't even get me started on the wire loom... it was like super glued together and then taped with gorilla tape around the outside and then layered with fiberglass. It seems like someone didn't want anyone to see whats inside.

OKAY! To the point ... I took the ground wire that didn't go anywhere and extended it and put a little terminal on it so I can bolt it on to a ground somewhere in the car. I searched and it seems like the ground is actually the block where the KS bolts to, but I was wondering if extending that black wire and then bolting it to another ground so that there will be TWO grounds instead of one will cause any problems. I was afraid of causing a short circuit but I am adding another ground not connecting the positive directly to ground and so... I am a little unsure but what do you guys think?

maxgtr2000

iTrader: (29)

I wouldn't mess with adding a ground, since it is grounded with the bolt in it. The problem was the actual harness anyway, not the ground, so I would just replace the harness or at least make sure there is continuity so that the signal reaches the ecu. I didn't realize my ks was dead for almost a year and I had to retune the car, it's like driving a new car now. You are losing pretty close to 10 degrees of timing advance with a ks code.

Leo_Koneval

iTrader: (4)

Yeah I think you are right but I'm really curious to see what would happen.

I hopefully repaired the harness good enough, I replaced the old wire with new same gauge wire and soldered everything up with heat shrink tubing and electrical tape just to make sure.

But one thing kind of bothers me, so the ECU reads the resistance from the KS and so the KS is wired up in a series with the ECU. The extra ground wire coming from the plug that goes to the engine harness would make the circuit a parallel circuit if I ground that wire. And since the resistance of a parallel circuit is lowest resistance in that circuit in theory it shouldn't make a difference.

Actually I am not sure if I'm thinking straight I think I might have breathed in too much solder fumes.

eddie982

iTrader: (10)

That ks is one elusive PITA, i couldn't get to it with a 1/4 socket wrench and extensions or a 12mm comb wrench, hoping this will get it out for sure with it's flex box end design...

cartman854

iTrader: (2)

Thats what she said...

Im going over to have my cousin help me replace mine, this will be take 2, we had to get some more expensive extensions, btw the thing pictured didnt work for us, I hate the knock sensor.... evil.

KilJim

Try it without the extensions

I'm a total noob but managed to do it, just need a whole lot of patience

And remember to use your left hand when putting the wrench on

eddie982

iTrader: (10)

Did you take off the green connector sensor thats in front first, that must've helped to get more of the arm in there? which arm did you reach in with and did you just use the socket wrench or comb wrench..

KilJim

Yupp you definitely need to take out the connector
Disconnect it on the top, take out a 10mm bolt at the bottom

Stood at the driver side of the car and used my left arm to reach in and position the wrench, it fits a lot better than using my right arm

I used a comb wrench, box end on the bolt
Stuck a thin metal bar through the open end all the way down till i hit something solid (no idea what that was, it just felt solid) and push the bar forward to break the bolt loose

The bar i used was the thing that comes with your scissor jack in the trunk. Anything will work of course, as long as it fits inside the open end

Pretty much the exact thing shown here http://www.youtube.com/watch?v=fPIMOIwLISc
Just that my wrench was shorter so i had to use a longer bar to break the bolt loose

eddie982

iTrader: (10)

great insight, i couldn't get that damn 10mm loose under the green conn. with a reg sized wrench, gonna get a stubby.

Leo_Koneval

iTrader: (4)

I think I figured this out!!

When I took off the ground wire that went around the outside of the clear insulated wire, it was like a coil like thing wrapped around into a web and I think that the ground wire that doesn't go anywhere actually DOES something, and it senses the magnetic force from the clear insulated wire.

When current flows it creates a magnetic force and I think how the ECU knows whether the KS is sensing knock or not is from the magnetic force it senses from the wire. And when resistance is highest current flow is extremely low and therefore there will be low magnetism but when resistance goes down current flow goes up and that will make a stronger magnetic force.

eddie982

iTrader: (10)

Did you figure all that out on your own! Big props lol.

Leo_Koneval

iTrader: (4)

I might be just talking nonsense, which I am pretty sure I am. I am just waiting for someone more knowledgeable to confirm or prove it wrong.

But yeah about the KS changing, I found out the easiest way for me is that if you have hands small enough to fit into that cave. Then you can get a small ratchet in there and then position it so that you just need to push the ratchet forward and it will break the bolt loose. What I do is stand in front of the car with one hand on the ratchet and then kind of lounge forward and the force usually breaks the bolt loose. But it'll look like you are humping your grille, which is good or bad depending on who sees.

Spyguy

iTrader: (1)

I just took a long ratchet and put the handle of a hammer at 90 degrees to the end of the ratchet and pushed forward. It works like a charm .

eddie982

iTrader: (10)

yeah i'm gonna try humping the driver side fender, kind of like in a superman position with the left arm outstretched and into that valley (Like KilJim, the KS Superman lol). Gonna wait for the Gearwrench XL Flex though, banking on it to work.

asand1

iTrader: (1)

When I butchered my KS sub-harness doing a permanent resistor mod, I noticed the same construction. One wire with clear insulation and shilding with the other wore connected to the shielding. There was quite a bit of electrical tape involved. I think yours was still factory original, they just look kinda hacked.
Sorry, the only photo I have is after.

eddie982

iTrader: (10)

Here's a couple more bad boys i found, a finger ratchet which i didn't know existed and a 12 inch flex head

maxtima4

I have to say that I am not a mechanic by any means but I am trying to learn much more about my maxima everyday. With that in mind I have been doing my own work on it , to a)save money and B) learn.

I had a knock sensor code come up when another code in my car came up. So like everyone else feels the ks is a big pain in the ***. I actually had something more in the way of getting at my ks. I am not even sure what it was, it just wouldnt come off to make it easier to change my ks.

So when I finally was able to get my ks off I also noticed the hack looking job on my ks harness and the fact that it looked like it only had one terminal on the ks side. So i bought another one from the dealer and when that one also came with the one terminal.

After the fact I do appreciate all the extra info you guys have provided.

I do have a little question though. Now that i have changed my ks, and i belive I have fixed my other code, should I get the codes cleared or will they clear themselves.

KilJim

You need to clear the codes yourself i believe

Only takes a couple of mins to do, no tools required
Worth doing just for the sake of learning

Leo_Koneval

iTrader: (4)

SUCCESS!!!!!!!!!!!!!!!!!!!!!!!!!!

So I cut the ground insulation off leaving just a little stub where I can re-solder a new ground wire if something went wrong. And I think the "ground" was a sensor wire to see how much current was flowing and by cutting if off, as in the metal web thing that goes and wraps around the clear wire. I think what I did was like the resistor mod except I still have a knock sensor.

Before I noticed my car was sluggish, like I could lean into it and make the car run as high as 4K RPM and it felt like nothing, it doesn't push you back into the seat like it did when my car was good.

But now there is that really hard pull at 3K RPM just like I remembered and the power is BACK!!! Best off all I still have a knock sensor but I'm not sure if I completely disabled its ability to retard the timing or if when there is a hard enough knock it'll still be able to retard it.

And also its been a few days and the pull is consistent and doesn't seem to be affected by temperature or anything. Its more power all the time. And MPG seems to be about the same.

jdooley

Yes, there is only one wire going to the KS. At some point close by, it's joined by a shield wire (the spriral wrapped one that was mentioned). This shield gets grounded and by that it means that the only magic that it performs is to keeps noise (electrical noise) off of that wire so the computer can tell the difference between a real knock and one that's just noise.

ajm8127

iTrader: (8)

Interesting theory, however incorrect.

The voltage made by the knock sensor is extremely low. The extra ground wire is actually a shield that keep any EMI away from the sense wire of the knock sensor. Without this shield, the sense wire would pick up stray electromagnetic interference and that would induce a current in the wire (Lenz's Law). This induced current would make the knock sensor signal too noisy to be of any use. A better design might be a knock sensor that amplifies the signal before it even leaves the sensor, but that would involve running power to it and it would make the sensor cost more.


This shield wire grounds on the ECU side and should be left disconnected at the knock sensor end. Shields are always only connected on one end to prevent the induced current from forming a ground loop. The sensor itself does get grounded through the mounting bolt, and the signal is sent to the ECU through the clear wire.

cashoit

yea, i was gonna say that there is only one wire for the KS. Its grounded through the body. I thought it was piezoelectric element sorta like an accelerometer and senses vibrations and sends signal back to ECU. Not really sure if power is need to KS...time for me to do a lil research...to the FSM!!!

ajm8127

iTrader: (8)

The knock sensor is a piezo element. Piezo element create voltage when they are deformed, so the sensor needs no input power. The theory is that a wave of energy is created when you have a knock, and this wave travels through the block and into the senor, where it deforms the element slightly (ripples on a pond). This slight deformation creates a small voltage that the ECU reads. The voltage is proportional to the severity of the knock, and the engine can pull timing as needed.

An accelerometer works totally differently.

On an interesting side note, there are prototype sidewalk panels that create electricity as people walk on them. They are also based on piezo elements. They could be used to light streetlights on day.

cashoit

yup. But some accelerometer use piezoelectric element too. Depends on which one u buy. The cheap (well no accelerometer is cheap) or the smaller ones use piezoelectric material.

Not sure leo had to ground the KS as much as replace the wire. replacing wire prolly made all the differnece.

Sidewalks that created electricity wd be neat

Leo_Koneval

iTrader: (4)

Aww I was wrong, but I work sort of kinda close to the answer haha!

Yeah I was too cheap and lazy to wait for a wire to come through mail or buy one so I just cut parts off the clear wire that was bad and soldered new pieces of wire in.

But here is the thing I cut off that ground wire since I thought about it and adding another ground would be bad so... I have no shielding for the clear wire except wire loom.... oh darn it

OH and you guys are right that KS is kind of like an O2 sensor it gives off voltage and doesn't need any power to be coming in to send out voltage. Can't believe I forgot that fact.