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      01-13-2012, 06:56 AM   #1
airudah2000
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Exclamation Rattling/knocking engine sound

Hi Everyone, I'm Kinda new here so please excuse any errors.

I've had my 318i for almost a year now. I travelled out of the country for the Christmas holidays and returned after three weeks to my car. after driving for a while I noticed some rattling noise in the engine. it was quite loud and sounded like someone was slamming a hammer on a piece of iron at the pace of 5 hits a second. I've never experienced this before. So i checked the dashboard computer, oil and coolant levels and all seems fine. This doesn't affect my driving at all though but it worried me so much, I had to stop driving it. At a point when i left the engine to idle a bit, the noise became so loud, I had to switch off the engine for fear of breaking something. I even thought I perceived a different smell from the engine...or maybe I was just being paranoid, I don't know.

But this morning, i decided to switch it on again. Surely, the rattle was still there. I revved up to 3000rpm and let it settle down again. This only seemed to aggreviate it more as the rattle became louder. Then I drove out and went down the street, put it on neutral (its automatic) and floored my throttle till it read 7000rpm. I heard a pop/cough sound from the engine, and let go of the throttle.

The knocking sound had stopped completely!

So I guess my question is, should I be worried about this? is it a common occurrence or did just happen because I hadn't driven it for 3 weeks? What causes this and how can i prevent it in the future?
Has anyone experienced a knocked engine on a 3 series before and could this be a sign my engine is about to knock?
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      01-13-2012, 01:45 PM   #2
Jon D
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It could be partially blocked injectors, which you might have cleared by flooring it.
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      01-23-2012, 01:25 PM   #3
airudah2000
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Update: The noise came back after a few days. I noticed it stops once i've driven for about 20 minuites. It usually occurs on cold starts or if i havent driven for about 3 days.
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      01-23-2012, 04:09 PM   #4
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Quote:
Originally Posted by airudah2000 View Post
Update: The noise came back after a few days. I noticed it stops once i've driven for about 20 minuites. It usually occurs on cold starts or if i havent driven for about 3 days.
As I said in my last post, this sounds like it could be partially blocked injectors. Depending on how clogged they are, they should be cleanable in-situ by the use of a high-pressure solvent rig. The reason why the noise diminishes after you floor the throttle is that you're increasing the fuel pressure, which has a similar, albeit reduced and temporary, effect to high-pressure cleaning.
How many miles do you have on the car and what sort of driving do you normally do?
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