Cold start knock E46

[Federation12 12]

I swear it's one thing after another with this car, I love fixing it, but this ones got me stumped!
I put it up on the bmw facebook discussion page but I got varied responses, so just looking for a second opinion here.

E46 320i M54b22, done just over 160,000 k's, auto gearbox.

On cold starts, a knocking noise can be heard from the engine, towards the back. It's irregular and the revs drop as you can see in the videos, however to this date it hasn't stalled, and after driving it (or even turning it off and back on) the problem essentially disappears.

Happens in park, affects the speed of reverse when not using the gas pedal, and seems to stutter slightly moving off after first start (only minor though)

I'm just stumped as to where to start, I've searched google, only finding results relating to the 4cyl engines. Nobody seems to have quite the same irregular knock that I have. I worry it could be from replacing the Oil Filter housing gasket, as I could have easily bumped something while cleaning up down there. No warning lights like other people have, and no knocks or noises at any speed once she gets going!

I'm really hoping it'll be easily identifiable through the videos, as you can imagine I want to get this fixed sooner rather than later! I'm quite happy to go through the list and start replacing tensioners and hoses but if I can get straight to the problem that would be much better!

Thanks in advance for any response.

https://www.youtube.com/watch?v=KYGc11vIU1E'>https://www.youtube.com/watch?v=KYGc11vIU1E

https://www.youtube.com/watch?v=Dy2C883RaCQ'>https://www.youtube.com/watch?v=Dy2C883RaCQ

Edited February 23, 2015 by Lewi9

[Allanw 1072]

It's always hard to hear nioises properly in videos, but that sounds like a backfire to me - wierd. Are you sure it's mechanical, or could it be popping in the exhaust (or intake)?

I'd check very carefully for an intake boot leak, though I don't think it is that - it's just VERY common.

I'd also plug it in and look at the live data, to see if there are any readings out of spec - such as Vanos advance, mixture etc. You don't appear to be getting a malfunction light, so I assume it's not registering as a misfire.

Does it do that as soon as you start it cold, or does it take maybe 10 to 30 seconds before it starts running wierd?

Also, if you start it cold, and drive off instantly, does it do it? (like start, put it in drive and go - no waiting)

Does it ONLY do it at idle? it you hold the revs at say 1000 or 1500 with no load (park), does it still do it?

The thing with an M54, is they retard the exhaust timing like crazy when cold to heat the cats up (dump unburnt fuel into the exhaust). They have been known to get bad enough to cause stalls, though it affects the 3.0 the most. Bad Vanos seals can cause this, though you don't normally get the popping or knocking (I really can't be sure from the video what the noise is). It could even be a coil pack, or spark plug that stuggles to ignite the cold start fuel mixture, but is fine when the engine is warmed up. Even an exhaust leak can cause popping as air ges sucked into the exhaust, but shouldn't affect the revs like that.

[Federation12 12]

First thanks so much for the detailed response!

It does sound mechanical, although now that you mention it, it could definitely be a muffled pop too!

I'll have a look over the intake boot today.

Yeah that's probably the next step, is get it plugged in. Is there a good place in Auckland that people recommend? North of the bridge is even better.

Quote

Does it do that as soon as you start it cold, or does it take maybe 10 to 30 seconds before it starts running wierd?

10 seconds is probably more accurate, it holds the revs higher when it first starts and as the idle drops the noise starts.

Quote

Also, if you start it cold, and drive off instantly, does it do it? (like start, put it in drive and go - no waiting)

Not so much, there is a bit of stutter through first gear, although it truely is minor and there's no noises coming from the engine as soon as you give it revs. I'll actually go out and test this in just a second.

Quote

Does it ONLY do it at idle? it you hold the revs at say 1000 or 1500 with no load (park), does it still do it?

That's actually what I've been doing recently to avoid it happen, if I hold it anywhere above 1000 in park, the noise doesn't happen.

Yeah this seems to be the problem I've ran into so far, is that the noise isn't easily identifiable and the problems can be so broad that it's hard to come up with a definitive answer. Interesting to know about the exhaust timing though! I think I would be more likely to hear an exhaust leak, right?

Edited December 17, 2019 by E30 325i Rag-Top
Quoting massively long preceding post

[B.M.W Ltd 950]

Sounds like back firing to me as well... should scan it first and check for airleaks

[Allanw 1072]

I really think scan it, like Glenn says...

it might be something REALLY easy...

Anything else is just guess work for the meantime.

(Also - if you have it scanned, the fault code doesn't always point to a faulty item - it needs to be interpreted and diagnosed - O2 sensor out of range codes can actually be a split hose, rather than a faulty sensor)

[Federation12 12]

Awesome thanks for the feedback guys!

Is there anywhere you recommend to get it scanned? I've got tomorrow off and willing to travel, are the scans relatively costly? Auckland area.

Just as a quick update I couldnt start it and drive immediately today, however I did start it and let it idle, no noises whatsoever so it definitely is tempremental!

Edited February 24, 2015 by Lewi9

[B.M.W Ltd 950]

Can do tomorrow (FREE) for the scan. Ring me in the morning. (09) 2722546 any time after 6.30am

[BMTHUG 1064]

Could be injectors. Had this happen today to a vehicle. Injector pulse was low on start up and then as you gave it more throttle the knocking went away

[Thesteggler 0]

Hey mate. Did you ever find the problem? On a cold start it does this for about 10 seconds or so. The rpms are meant to sit at around 1000 because that's how the engine warms up quickly. I've only got error codes p0369 and p0340. Any help would be very appreciated 

[B.M.W Ltd 950]

They are camshaft position sensor fault codes. Get it checked professionally or throw money at it and replace both camshaft sensors and recheck. Is it just a code reader you are using or can it provide live data and clear fault codes and adaptions ? After replacing the sensors, fault codes AND adaptions MUST be cleared before starting and driving again.

BTW Federation12 hasn't visited here since July 24, 2016

[Thesteggler 0]

Hi mate,

It’s just an obd2 scanner with torque pro. About a month ago, my car would randomly stall when i did warm starts. One day it completely died and the engine would crank but wouldn’t start. Me and 3 euro mechanics stripped the car and found out that it was the knock sensor, vanos and crank position. Couldn’t reset the vanos as the car would stall at 80 degrees. Fast forward a week after the repair and I got this exact same knocking issue that old mate was talking about. It only does it on cold starts and starts about 10 seconds after engine starts running. Lasts about 10 seconds or so. I’ve had the camshaft sensor errors before the car died and even  after taking every single sensor out of the car and cleaning them, they reappeared a few days later (could there be an oil leak making them dirty.). Sometimes I have a 2 -3 second crank on warm starts but the car drives well. Someone mentioned an oil separator as a potential issue for the knocking noise, coil pack has also been thrown around. What are your thoughts ? After the repairs I had p0300, p0340, p0369, p1083, p1085, p1343, p1347. My mechanic who’s a mate scanned the depths of it with a bmw tool and gave the car back to me with no errors apparently. Kind of nervous because just before the car broke down, I had the 2 camshaft errors before getting the crank position error. I cleared all the codes and gave my car a run and the only two errors reappearing are the camshaft sensors. We reset the transmission and a few other things. I’d pay for any advice on the knocking noises and camshaft errors. Cheers

[B.M.W Ltd 950]

I would suggest you choose one of these specialists to look at it for you:

https://www.euromechanica.com.au/mechanics/bmw-mechanics-brisbane?gclid=Cj0KCQiAuefvBRDXARIsAFEOQ9H_ASf78V-AR7WZMgrRtZHBx86yVTJ1aZtLeLM_-QvWP8gbZkZf6ZkaArjuEALw_wcB

[Thesteggler 0]

Any advice on doing it myself though? 

[B.M.W Ltd 950]

No offence intended but I think my best advice is in my previous post.

[Deccody33 0]

Did anyone figure it out? Thanks 

 

[Federation12 12]

Morning!
I still float around on these forums, didn't ever get a notification that this thread was still going until I saw Cody's PM.
The car has been sold now sadly, but I did get to the bottom of these issues before it was sold. I still keep my eye out for a 135i at the right price, and I'm hoping that the E39 ute project gets resurrected at some stage

The main things that fixed it were a PCV system overhaul (i accidentally bought the cold weather one but it fit up fine), and new ignition coils. I did both of these at the same time so I couldn't say which one sorted the issue. 
At the age of these cars now, if both of these haven't been done then they're a worthwhile task. 

 

[Deccody33 0]

Thanks again for replying mate. Finally a solution to this.

 

Edited April 3, 2020 by Deccody33