Can someone show me a picture of a knock sensor on an L98? Its the big sensor sticking out of the passenger side of the block right? There's no wire going to mine. I'm getting code 43.

EDIT: The car runs fine. The SES light comes on at random and goes back off.

 

It looks like this:



It's on the passenger side. You'll have to crawl under the car to see it.

 

I can see mine from the top. Shouldn't there be a wire running to it? I don't have any loose wires hanging though.

 

Yes there should be a wire going to it, thats why you're getting a code 43.

What year is your car? Someone with a similar year could look at their car to see which harness the KS wire comes from and where since apparently whoever unhooked your KS cut / hid the wire. Worst case you could run a new one from the ECM / ESC, but you have to have something hooked to the KS wire or your computer will never work 'right'

 

Its a 91. I think its supposed to be a dark blue wire, but I don't know where it runs, and there's no wire hanging that I can see. You're probably right about the wire being cut and hid. The worst part is that it had to be the dealership who did this. No one else has worked on my car besides them and myself. I should make them fix it, but I don't want them to mess up something else.

 

If you're knock sensor was disconnected, you would be getting a lot of knock when you put load on the engine.

 

I've been reading the related threads. The way I understand it is that the MAF cars have the blue wire running to the ESC and then to the ECM. While mine (91 w/ MAP) has a white wire going from the KS directly to the ECM, and I do not have an ESC. Is this correct? The only schematics I can find are for the earlier MAF cars. Any more help on this would be greatly appreciated.

 

Umm, yeah no... not true at all. The knock sensor is there to dect any knock that you MIGHT have. A properly running engine will not have any knock, there for rendering the KS inactive. When the KS hears knock, or is not hooked up, the total timing is lessened accordingly.

 

I've had it unplugged and it pinged like mad. My friend in his 89 TA had bad knock and I told him to check his knock sensor, and sure enough, it was unplugged(no idea how it became unplugged) fixed the problem right there. From what I know (which isn't very much), the ESC advances the timing to a point where the knock sensor picks up a light knock (inaudible) and tells it to retard a bit. I'm no certified mechanic though. Someone who knows how it works, please give me a lesson on this.

 

The computer will only advance the timing to a certain degree. This varies on many things such as base time, and the spark tables defined in your prom. When the KS hears what it thinks to be a knock, it will retard the timing untill that knock is gone. This is called Knock Retard (Im not calling you a retard ). On a perfectly running/tuned engine, there will be no Knock, and no Knock Retard. Beings that Knock Retard is taken from your total timing, this dramatically hurts performance. When the sensor is unplugged, the ECM assumes that there is knock, therefor retarding timing. Once his knock sensor is hooked up again, he will get a MAJOR change in performance.

Take my car for example. Im getting a max of 16* of timing retard at WOT. This is cause by a lean condition I am currently working on. My spark advance, which should normally rise as the RPM increases, is staying at 39* through out the RPM range, including idle. All problems have led towards my ECM, which will be replaced next.

 

Yup I'm wrong. I understand what you said in your post and I researched it a bit. This is the one thing I learned today

 

 

Just to make sure there is no confusion. I believe this is my knock sensor.

 

Also, I did find this red wire that's not connected to anything. I don't know what its for.

 

Ummm yeah... that would NOT be your knock sensor. That's your fan switch. It wouldn't make any sense for a knock sensor to be screwed into the head would it ? (that sentence sounds funny for some reason).


If it's unplugged then dont worry about it, unless your car is overheating.

p.s. you can see part of your knock sensor if you look REEEALLY close between the header pipes of the middle two cylinders. Right about the weld ring on the pipe of cyl #4 you will a small white shadow. That's your knock sensor.

 

I have that wire on my car too. It was never connected to anything. It must be some sort of diagnostic connector or something.

 

88 WS6 TransAm GTA

You stated that with the knock sensor unplugged, the ECM assumes there is knock and therefore pulls out timing. I just ran my car at the track Tuesday with the knock sensor unplugged. I logged the pass using Diacom, and did not have any knock retard or total timing pulled out. I was under the impression that having the knock sensor unhooked would keep the ECM from pulling bacl timing, but would also cause the check engine light to come on after a while.

 

My fan works properly though, and there is a similar sensor on the driver side head which I thought was my fan switch.

 

The sensor on the driver's head is for the temp gauge. The passenger side sensor, which isn't connected on yours, is for the secondary cooling fan.

 

 

Boxeat2469 is correct.

 

I see. Thanks for straightening me out. The fan switch looks very much like the picture Ozzy88GTA posted. I'll crawl under there tomorrow knowing what to look for this time, and hopefully the sensor is just bad and I can replace it.

:hail:

 

OOOOOOOk here we go...
Boxeat, Im not sure why your not getting a 43 at WOT, thats when the engine is most proned to detonation. If your sensor was bypassed, I could see why, but just being unhooked *shoud* automatically put the car basically in limp home mode. Unless you have a custom prom with KS disabled, the I really dont have an explanation for ya.

Ok... now for the first picture LT1LE Posted, that isnt your knock sensor. The one you have is one of your fan sensors. The connector which goes to the knock sensor usually breaks and basically disintegrates... hence that bare red wire im guessing. The last pic abocve titled "Knock Sensor?" is correct. Go to GM dealer, or a junk yard, and get that connector. Acually what you can do to see if that really is your KS wire, is get a wiring diagram and find out which terminal is goes to on the ECM, then test for continuity.

It is on the passenger side of the block near the oil dipstick, which is what you have a picture of. The coolant temp sensor which runs the guage is on the front drivers side head. Also, try to get your car on a scanner, to see if your getting knock retard, which you should be.

 

Be prepared for a long shower of coolant when you unscrew the knock sensor, unless you have a catch pan standing by of course

 

I wish I would have remembered that when I went to change my KS for the first time... let the car cool down too... the coolant gets hooooooooot!

 

When I changed my buddies on a hoist, I had the replacement one ready to install and that reduced the amount of lost coolant.

 

The knock sensor not being connected won't set a code 43 in and of itself. There is a routine that the knock system goes through at times during part throttle operation, this routine performs a self test of the ESC system and is looking for input from the knock sensor, if it doesn't see the input you get a code 43. Now if the knock sensor isn't hooked up and you never ever get a code 43, someone has bypassed the sensor somehow or the ESC has failed internally to think it sees knock input.

 

The red wire is your fuel pump bypass wire. If you jumper a 12V + wire from the battery to it the fuel pump will run constantly. It's handy to drain the gas from the tank before dropping the fuel tank to swap out the pump. Just disconnect the fuel filter and run a rubber hose from the line into a small gas storage container. Also handy to test if there is a problem with the fuel pump. Lon

 

Depends on the year (possibly). Speed density will definitely throw a code within seconds of start-up if the KS is not hooked up. Reason being, the node floats, the voltage goes high, and the ECM sees that over voltage as EXTREME knock, knows there shouldn't be extreme knock, and thus declares the KS defunct.
IIRC MAF acts as you describe, where it has a self test that it goes through under certain load/running conditions. But i am positive that is not how the 730 works...

 

ok this is weird...i JUST replaced the KS on my '87 Formula LB9 and i had NO COOLANT come out of the block, and i had plenty of coolant and my car runs cool...

 

You had better check that hole again... that might be the reason your knock sensor isnt working properly... that hole could be plugged with sludge or dirt or anything, which will affect how the sensor works.