Loud Knocking sound coming from engine

[Sexymeatball]

I need some preliminary help on this one guys. I was away on vacation for two weeks, got back yesterday morning and went to start my car this morning to drive to work. Upon turning the key, a loud knocking sound immediately made itself known from the engine bay. It was clearly audible above all other engine noise and hit every half second or so, increasing in speed with the RPMs. Since I had to go to work, I quickly shut it off, screamed some obscenities, and took the SHO to work. I had no time to attempt to diagnose beyond the obvious noise.

The engine has 43k on it and was running like a top with no unusual noises or anything before I left for vaca. The car sat in a garage for two weeks while I was away and somehow developed this problem. Obviously, I will attempt to diagnose tonight, but in the meantime I was hoping for some direction as to what this might be, especially if it might be a model specific issues.

Thanks in advance

[mtmpow3r]

Check your vanos

[Jrdeamicis]

Did you make sure you had enough oil?

[Sexymeatball]

Check your vanos

that was my first thought this morning (and my hope since its an easy and relatively cheap fix), but i've read that that sounds more like a can of marbles or a diesel engine. This was a distinct and consistent knock.

Did you make sure you had enough oil?

Well it had enough oil before I left for vaca. I'll check it again when I get back home though

[GacAttack]

You're describing the sound an engine makes when it's using too low an octane fuel. Did your wife maybe fill it up before vacation with 87 octane? You probably wouldn't hear that loud a knock on a stock engine, so this would be more likely if you've done some tuning.

It would help to have an audio file we could listen to. Can you record the sound and post it (when oyu're back at home)?

Good job on noticing that it's directly proportional to the engine's RPM. VANOS is always an option; there are a ton of threads out there that detail exactly what a failing VANOS sounds like, complete with audio files. Check those out and see if it's the same as on yours.

Did you notice any CEL or other warning lamps?

[Xiphos]

If it were the Vanos, it would have stopped making the sound at 4k when it disengages. I highly doubt 87 octane would cause knocking loud enough to hear over the engine, and fuel doesnt seperate enough in 2 weeks to cause weak fuel.

I'd make sure you didnt leak all your oil out or something.

[GacAttack]

You're describing the sound an engine makes when it's using too low an octane fuel. Did your wife maybe fill it up before vacation with 87 octane? You probably wouldn't hear that loud a knock on a stock engine, so this would be more likely if you've done some tuning.

It would help to have an audio file we could listen to. Can you record the sound and post it (when oyu're back at home)?

Good job on noticing that it's directly proportional to the engine's RPM. VANOS is always an option; there are a ton of threads out there that detail exactly what a failing VANOS sounds like, complete with audio files. Check those out and see if it's the same as on yours.

Did you notice any CEL or other warning lamps?

[Xiphos]

Holy deja vu batman.

[GacAttack]

Xiphos: I still love that sig. That whole thread was fun.
Also, if they engine has been tuned for higher octane, then YES you could hear the knock over the engine. My friend's mustang is just software tuned for 93 and you can DEFINATELY hear the knock if it's using 87 (he wanted to see if it would, so he ran it dry then put in one gallon of 87. Oh man was he worried when he heard it!)

Also also, and I may be wrong here, but doesn't VANOS engage at 4k and up? But anyways, the VANOS still has moving parts linked to the cams that could cause RPM-related noises. It's a common enough part of failure that I don't think it's worth ruling out without more info from the OP.

[GacAttack]

Holy deja vu, indeed. Oops.

[Xiphos]

Xiphos: I still love that sig. That whole thread was fun.
Also, if they engine has been tuned for higher octane, then YES you could hear the knock over the engine. My friend's mustang is just software tuned for 93 and you can DEFINATELY hear the knock if it's using 87 (he wanted to see if it would, so he ran it dry then put in one gallon of 87. Oh man was he worried when he heard it!)

Also also, and I may be wrong here, but doesn't VANOS engage at 4k and up? But anyways, the VANOS still has moving parts linked to the cams that could cause RPM-related noises. It's a common enough part of failure that I don't think it's worth ruling out without more info from the OP.

Regarding the 87 octane, you are talking about a Ford. Seriously, BMW's are real cars haha. I personally hae put 87 octane in my tank before and never had any knocking, maybe if it was sitting for a while it may cause knocking.

Vanos I believe is under 4k, guess we'll find out! haha. Yes, it is still moving, but it wouldnt seem likely that the vanos would go out with only 43k miles on it.

[zkc]

This is probably not what it is but I had a similar problem when my car sat for over a week while I was out of town. Mine turned out to be the fan just clipping the hose leading from the radiator to the thermostat. The hose had become a little soft over time which allowed the fan to just start to touch it, but it was a simple replacement. I'm assuming the lack of use and pressure in the hose while it sat made it worse to where it finally came in contact with the fan...

[Sexymeatball]

thanks for all the suggestions. I'm anxious to get home and spend some time diagnosing / fixing. I'll keep this thread updated once its fixed, or i'll post an audio clip if its not

[Sexymeatball]

Update:

Well the noise it made this morning is gone. But I found this clip: http://s143.photobucket.com/albums/r...rent=Noise.flv
and it sounded EXACTLY like that.

Now its making a noise that sounds exactly like this:
http://s98.photobucket.com/albums/l2...rent=noise.flv

I'm guessing its time to pay the DRVANOS a visit?

[Sexymeatball]

thoughts on the noises? the thread i pulled these from was not specific about what the linked noises were.

[GacAttack]

That second click you referenced sounds OK, but, admittedly, I am drunk right now.

Dr VANOS is always seeing patients. You don't even need an appointment!

[Sexymeatball]

That second click you referenced sounds OK, but, admittedly, I am drunk right now.

Dr VANOS is always seeing patients. You don't even need an appointment!

You sir, are an inspiration. Godspeed.

[mtpktz.]

I have no idea what the first video is, but I'm fairly certain that the second video is a failing Vanos.

Best of luck and keep us updated.

[M3MPHIS]

Update:

Well the noise it made this morning is gone. But I found this clip: http://s143.photobucket.com/albums/r...rent=Noise.flv
and it sounded EXACTLY like that.

My 97 M3 is making this exact noise, has anyone figured this out for you yet?

Someone help!

I'm going to check the spark plugs, oil looks fine, I'm going to check the oil separator... I don't think its the vanos

[Hova]

My 97 M3 is making this exact noise, has anyone figured this out for you yet?

Someone help!

I'm going to check the spark plugs, oil looks fine, I'm going to check the oil separator... I don't think its the vanos

sounds like rod bearings knocking.

[Hova]

You sir, are an inspiration. Godspeed.

but yes, 100% vanos, visit www.drvanos.com

[GacAttack]

I'm sober now, and I stand behind my last post. Dr VANOS FTW.

[Hova]

I'm sober now, and I stand behind my last post. Dr VANOS FTW.

[M3MPHIS]

sounds like rod bearings knocking.

thats worst case right?

[M3MPHIS]

I've also read in some other threads that it could be loose crank pully bolts, or my serpetine belt.

any of those sound like they could be the problem?