Anyone notice any Engine Knock?

[Devil Dog]

I had the same problem. Started running 76 100 octane fuel, sound went away. Must admit, I was also using Shell and each time it sounded worse and worse.

[quackbury]

I've been running a steady diet of Shell V Power. Guess I drank the Kool Aid. The last couple weeks I've been noticing some mild drivability problems. Slight backfiring when I back off the throttle, a little bucking when cold, occasional momentary drop in power under WOT. Almost like fouled plugs or (shudder) carbon deposits.

I'm going to give it what we used to call an "Italian tune up" tomorrow (probably waaaaay too politically incorrect these days). Will also switch from Shell and see if that makes any difference.

[Amrrrrr]

Rovman, thank you for your excellent account of the knock problem. I have 6000 miles on my convertible '08 M3 and for the last couple of weeks I am getting this weird very frustrating cheap car kind of knock every time I try to accelerate from lower speeds on 2nd or 3 rd gear, especially when there is a slight incline. True, I have been filling 93 octane Shell gasoline lately more consistently, though occasionally in the past without problems. I switched back to Mobil but the problem persists, very disheartening indeed. I have an appointment with the service department next week, but I do not want to go through what you had to go through, and I do not want them to tell me it is "nothing" either. First, can you give me an update on your M and the knock problem current situation, fully resolved or is still rearing its ugly head? Second, what would be my approach to service personnel regarding this, so I can cut the crap?
Thank you for your advice and time.

[King Tut]

Originally Posted by Amrrrrr

I am getting this weird very frustrating cheap car kind of knock every time I try to accelerate from lower speeds on 2nd or 3 rd gear, especially when there is a slight incline.

How does a cheap car kind of knock differ from an expensive car kind of knock? Can you describe it? Do you feel a loss of performance or are you just hearing knock with your ear?

[Amrrrrr]

By that I meant it is unbecoming of the M3 and it never happened under similar conditions of driving before. The performance is transiently worse. But it is the new noise that is more persistent and annoying.

[JCtx]

After reading this thead, my question is how effective is the in-plug knock sensor on EACH cylinder of the M3 engine? Compared to 1 or 2 (1 per bank) sensors on other engines, this one has EIGHT (one per cylinder). It's supposed to be the perfect solution to knock/ping. Just curious. Or maybe it's something else, like a loose cam chain (bad tensioner)???

[alpineweissM3]

Mine is still knocking and pinging away. I have tried Shell, BP, Mobil, and of course Sunoco with no change whatsoever. I have even tried a couple tanks of 91 and it knocks just as much as with the 93. Trying a different dealer next week...hopefully their service dept will figure out what is wrong. Just thinking about what "elp" said about the knock sensors...why won't the dealer just try replacing the plugs to see if that makes a difference? I am so frustrated.

[FrenchBoy]

Originally Posted by trackfiend

1.1 Knocking type sound at idle
When the engine is at normal operating temperature and depending upon the accessory loads on the engine it is possible a low frequency knocking type noise may be heard in the car. This noise is a characteristic of the engine and is not an indication that there is a defect with the engine. In the event that you receive an inquiry about this noise it is important to reassure the customer that this
noise is a characteristic of this engine. The noise in no way affects the durability of the engine and will not lead to a failure of engine components.

Thanks for this. I have been wondering about this "somewhat cheap sounding" knocking at idle, particularly when the engine it hot.
Glad to know it's as intended, albeit not the best sound.

[elm3]

Originally Posted by J08M3

I've noticed a noise under hard acceleration, 75%-100% throttle starting around 3,000 RPM. It almost sounds like a slight vibration/rattle sound coming from the engine. Has anyone else noticed anything like this? I'm wondering if it's possible this is engine knock? First thing I tried was a full tank of gas from another gas station to see if there was any difference. I only use 93 octane gas. I noticed no difference between Hess gas where I normally go, and Mobil where I go sometimes. I don't have many other options near me.

Or is it possible this sound is completely normal? Anyone else notice something similar to a rattle under hard acceleration?

That is normal, it is actually your airbox making that noise. It is the filter rattling a little bit. Nothing major with your engine.

[zuggerat89]

o no, more VANOS rattle?

[doba_s]

Originally Posted by FrenchBoy

Thanks for this. I have been wondering about this "somewhat cheap sounding" knocking at idle, particularly when the engine it hot.
Glad to know it's as intended, albeit not the best sound.

whether it is normal or not, but my car was lemoned because of that sound ... dealer replaced bunch of part in my engine ... the sound went away for a few months and then came back again ...

new car doesn't have that

[FrenchBoy]

Originally Posted by doba_s

whether it is normal or not, but my car was lemoned because of that sound ... dealer replaced bunch of part in my engine ... the sound went away for a few months and then came back again ...

new car doesn't have that

Interesting. Can you elaborate on this?
What was the rationale for using the lemon law? Was the car not performing to its specs and BMW NA was not able to fix it? Any threads on this?

Thanks.

[RGuard250]

I noticed it when I ran my car down in Mexico... poor car

[BPMSport]

I've had nothing but bad experiences with Shell.

It sent my supercharged 330 into limp mode. And it's sent a couple 335's into limp mode as well.

I avoid it at all costs and only use Chevron or 76. On the east coast I used Sunoco 94/93.

[MRSSIIM3]

bump any solution on this?

what exactly does the knock feel like? my car has been feeling weird in gear 1 when i floor it above 4k. theres a weird sound coming from engine bay under this circumstance

[fugeo]

DINAN has software for this. It retards timing only in the specific range and claim there is no power loss. I have not tried it yet because I have to send my ECU overseas.

[lve2xlr8]

Originally Posted by elm3

That is normal, it is actually your airbox making that noise. Nothing major with your engine.

1 it's exacerbated by aftermarket filters. You can really hear it when going from wot and abruptly lifting off the accelerator at 32-3300 rpm. I think it's a vanos related noise kinda like VTEC aha

[MRSSIIM3]

Originally Posted by fugeo

DINAN has software for this. It retards timing only in the specific range and claim there is no power loss. I have not tried it yet because I have to send my ECU overseas.

for what? the issue i was describing? is what i am experiencing normal?

[fugeo]

Originally Posted by J08M3

I've noticed a noise under hard acceleration, 75%-100% throttle starting around 3,000 RPM. It almost sounds like a slight vibration/rattle sound coming from the engine. Has anyone else noticed anything like this? I'm wondering if it's possible this is engine knock? First thing I tried was a full tank of gas from another gas station to see if there was any difference. I only use 93 octane gas. I noticed no difference between Hess gas where I normally go, and Mobil where I go sometimes. I don't have many other options near me.

Or is it possible this sound is completely normal? Anyone else notice something similar to a rattle under hard acceleration?

I was referring to this thread, I have the same issue. It is not normal and a dealer will not be able to fix it.

[m3cragg]

I get the same thing around 3k-5k when the oil temp is on the colder side, It tones down considerably once the car has warmed up to 100 canadian (210F) to almost nothing

[m3an]

Bumping this thread for some others insight. Since I have had my car, I notice a very slight audible knock when the car is under a light load (say 2k rpm in second gear @ 75% throttle) for 1/2 a second on throttle input. It is very slight, and all diff brands of gas don't seem to matter. Dealer thinks I am crazy (car is under warranty, nothing's been done) and I know what I hear. Again a light knock under a light load that goes right away, I'm stumped. Considering the elaborate knock sensor design on this car, it is kind of odd.

Anyone Else? Please let me know after you drive your car. Again, both my M cars have sounded like sewing machines (normal) but this is a little odd.

[US///M3]

I dont think the op's problem is caused by bad gas.