Knock Fault and Timing Chain

[Lopaka]

Hey guys/gals. I've had a knock fault on the check engine. The local BMW dealer says nothing is wrong w/ my car. BMW changed the sensors and it still faults(check engine stays on which is a long story as it never was on until BMW changed the knock sensor, anyway too long to explain).

Anyhoo, I noticed early last week, that the timing chain seemed to be slapping against the case when I revved and then let off the throttle. I presume it's the timing chain tensioner so I've ordered the parts, and will be tearing into the engine tomorrow to change the water pump, timing chain (upper/lower), and tensioner. So, my question is:

Would a tensioner/loose timing chain cause a knock fault?

2 out of 3 Independant BMW shops say no, while 1 is adamant that it is the cause.

Any opinions on this?

[Bernanke]

Originally posted by Lopaka
Hey guys/gals. I've had a knock fault on the check engine. The local BMW dealer says nothing is wrong w/ my car. BMW changed the sensors and it still faults(check engine stays on which is a long story as it never was on until BMW changed the knock sensor, anyway too long to explain).

Anyhoo, I noticed early last week, that the timing chain seemed to be slapping against the case when I revved and then let off the throttle. I presume it's the timing chain tensioner so I've ordered the parts, and will be tearing into the engine tomorrow to change the water pump, timing chain (upper/lower), and tensioner. So, my question is:

Would a tensioner/loose timing chain cause a knock fault?

2 out of 3 Independant BMW shops say no, while 1 is adamant that it is the cause.

Any opinions on this?

many other have done same thing when people said it would not help, They did it and it worked. The reason shops say no is b/c they want to have to take all that crap apart just to fix a chain tensioner.

[Lopaka]

Originally posted by SupaBimma



many other have done same thing when people said it would not help, They did it and it worked. The reason shops say no is b/c they want to have to take all that crap apart just to fix a chain tensioner.

Supabimma: So are you saying that others have had a knock fault and changed the tensioner and it went away, or are you saying that in general shops say something won't work, because they want to do it? I would like some assurance that it will go away since I'm in the engine already (see my other post). And I could go deep into the engine if I had to (would hate to stop at the timing chain and put it all back together, just to take it apart again).

Thanks

~Lopaka

[Bernanke]

im talking about knock, b/c i have same thing and even my shop says that but i know its tensioner b/c timing chain does not strech enough past the tensioners capabilities or it would snap. im pretty sure its that, b/c timing chains are supposed to last at least 100K miles. exactly what does the noise sound like and what rpm does it come and when does it go away (if at all) and describe the sound. i can try and pinpoint it but its kinda hard to tell with engine noises could be tons of things.

Originally posted by Lopaka


Supabimma: So are you saying that others have had a knock fault and changed the tensioner and it went away, or are you saying that in general shops say something won't work, because they want to do it? I would like some assurance that it will go away since I'm in the engine already (see my other post). And I could go deep into the engine if I had to (would hate to stop at the timing chain and put it all back together, just to take it apart again).

Thanks

~Lopaka

[Lopaka]

Originally posted by SupaBimma
im talking about knock, b/c i have same thing and even my shop says that but i know its tensioner b/c timing chain does not strech enough past the tensioners capabilities or it would snap. im pretty sure its that, b/c timing chains are supposed to last at least 100K miles. exactly what does the noise sound like and what rpm does it come and when does it go away (if at all) and describe the sound. i can try and pinpoint it but its kinda hard to tell with engine noises could be tons of things.

So you too have a check engine w/ a knock fault?
Just wondering, because it was very hard to diagnose what exactly is wrong if anything. There is no sound from the block. But the timing case will vibrate when revved (no sound) but when you let go of the throttle a vibration/buzzing sound. It happens only when the car is very hot 1/2 or more, causing the chain to rattle against the top of the valve cover (but the knock fault is on constantly which perplexes me).

This is what I did so far: 1. replace knock sensors 2. Break Box check 3. swap the DME to check DME for possible failure 4. re-replace knock sensors 5. knock sensor check via computer diagnostic; check within guidlines and vibration is not outside limits to warrant a genuine knock fault. 6. etc. etc.

[Bernanke]

Originally posted by Lopaka


So you too have a check engine w/ a knock fault?
Just wondering, because it was very hard to diagnose what exactly is wrong if anything. There is no sound from the block. But the timing case will vibrate when revved (no sound) but when you let go of the throttle a vibration/buzzing sound. It happens only when the car is very hot 1/2 or more, causing the chain to rattle against the top of the valve cover (but the knock fault is on constantly which perplexes me).

This is what I did so far: 1. replace knock sensors 2. Break Box check 3. swap the DME to check DME for possible failure 4. re-replace knock sensors 5. knock sensor check via computer diagnostic; check within guidlines and vibration is not outside limits to warrant a genuine knock fault. 6. etc. etc.

I doubt its timing chain. B/c timing chain rattles all the way to readline, its a real knocking sound (not as bad as rod knock but its pretty bad). your problem might be lifters (i also have that) but its not timing chain b/c timing chain would make noise no matter what. hope that helps

[switlikbob]

I have noticed a strange rattle / knock /vibration sound coming from right under the valve cover in teh front of the engine...the engine runs fine and I can only hear the noise at RPM's just above idle...I would saysomewhere around 900-1000. I got under the hood with the car running and gave the throttle linkage a small pull...as soon as I get above 1000 rpms (I'm guessing at the RPM b/c I am under th ehood and can't see the tach), the noise goes away...I get off the throttle and I can hear the noise again at 1000 down to 900 RPM and the it's goine at idle...I am guessing that it is the timing chain tensioner or the chain itself, like you guys said, since I am not having any other engine issues (the knock sensor CE code was thrown once, about 6 months ago, and was gone the next time I started the car...never came back again...I just want to know if this is something that can be let go for a while or if I should address it now. The car has 94,xxx miles...TIA...Bob