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  7. 2007.07 E92 M3 - Cold start knock - HELP!

2007.07 E92 M3 - Cold start knock - HELP!

BMW
Themenstarteram 3. Juli 2014 um 15:32

I understand this is a german forum, but I have been dealing with this issue for over a month, and tried many things, and am out of ideas. Maybe someone who is closer to the mothership ( BMW @ Germany ;) ) can help. I do not speak german :(

I am experiencing a multi-knock during cold starts. It lasts about 0.5 seconds, happens about 1 second after ignition takes place (so about 1.5-2 seconds after pressing start). The noise is quite fast so at first it sounds like a single noise, but I have recorded and examined the sound visually, and there is actually a sequence of knocks in succession (image attached below for reference).

Theres quite a bit of info as I have been trying to methodically deal with the issue as best I can.

Description of the issue:

a) The noise only happens on cold starts after the vehicle has sat for about 6 or more hours.

b) The noise only happens the first time the vehicle is started. In the following sense: START -> KNOCK -> OFF RIGHT AWAY (few seconds) -> START AGAIN -> NO NOISE....

c) Previous engine run cycle has an effect on it. In the following sense: If I cold start it now, get the knock, turn the vehicle off without actually driving anywhere (keeping the motor from heating up at all in essence), wait another 8 or so hours, start it again, the knock will be much quieter.

d) There are quite a number of people who are experiencing the same issue. Some say this is "normal". But many E92 M3's do not have this noise. I have talked to many people on m3post.com about this. Many people have this noise. Here is one example on youtube, this video is 4 years old, many years before I bought my M3 : https://www.youtube.com/watch?v=gvqsN7j0sYA <-- NOT MY CAR, someone elses car, same problem :(

Here is what I have done to attempt to resolve the issue:

1) Changed the check valves. Those that know this motor know there are 4 of them, one on each side of each head. They have been replaced. Cheap parts, expensive labor.

2) Tried adding oil.

3) Changed 2 vanos tensioners.

4) Remove starter, clean, grease. Starter in good condition.

5) I have installed a tune by bpmtune and had cold start deleted. So this is not related to the secondary air pump. Noise was / is present before and after the tune was installed.

6) I have removed my intake manifold and placed my head near the motor while my GF started the engine. The noise was there, very clearly, but due to the number (not necessarily volume) of noises coming up as the motor started... I could not determine where it was coming from. If I were to guess, and cant say this 100%, I would say somewhere from the drivers side valve cover.

Here are the videos / images that give quite a clear representation of what the issue is.

As always, any help is greatly appreciated.

PS: I know a noisy vanos is normal as oil fills back up. I am talking about the very obvious CLACK-CLACK. Some videos show it being better, one of them quite bad (longer, multiple clack-clack-clack...).

Videos:

Not so bad:

https://vimeo.com/97717663

Worst:

https://vimeo.com/97717665

Real Bad (someone on another form sudgested pumping the break prior to starting, the actual noise takes place around 0:49):

https://vimeo.com/97849126

With intake manifold off:

https://vimeo.com/99052912

Here is a wave form of the noise (from the really bad one):

http://i.imgur.com/mahosEY.jpg

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15 Antworten
Themenstarteram 3. August 2014 um 11:21

This is not starter related.

The starter was removed, cleaned and greased. It is in excellent condition.

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  7. 2007.07 E92 M3 - Cold start knock - HELP!