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7 Series - E38 (1995 - 2001)

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  #1  
Old 02-24-2013, 12:31 AM
CharlesAFerg CharlesAFerg is offline
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Mein Auto: E34 ///M20 2.5i '89
Knock sound, odd starting.. Not VANOS.

All,

My '00 740i Sport is occasionally (not every start, and I can't nail down a common theme) making what sounds like a knock when starting. I know what the vanos noise sounds like, and this is not the same.

It's not as the engine is started, but as the starter is cranking. If I could explain it better, I would say that the engine stumbles when it starts, and sometimes makes a knocking sound, almost as if the wrong cylinder fires out of order before it would normally start. So, say I start the car and it starts normally after about 4 or 5 cranks of the starter. What is happening here, is that after maybe after 2 cranks, a cylinder fires and the starter seems to continue for another 2-ish cranks while the rest of the cylinders begin to fire in order, smoothly.

I was told the car was running lean, but would that cause this starting issue? I'm not entirely sure how that system works, and perhaps I'm missing something. I see no codes with either the BMW specific diagnostic tool or a generic OBDII scanner.

Other than that, the car runs great. I am replacing my aux evap pump due to failure, although I'm almost certain that it is unrelated.

Advice would be greatly appreciated!
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  #2  
Old 02-24-2013, 07:41 AM
Espresso Espresso is offline
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Mein Auto: 2001 740i Sport
does it sound like this?

http://www.youtube.com/watch?feature...&v=EURgDRgE5lc
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  #3  
Old 02-24-2013, 05:10 PM
seamus2154 seamus2154 is offline
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Mein Auto: 2001 740I Sport
My 01 sport does what is in expresso's video. Only for a second or two and first thing in the morning and a cold start. I was told it is my chain tensioner. I have read the same thing. The new tensioner is longer w/ a tighter spring I have read. It is not a hard job it's on the pass head and can be done externally. The part is about 75 bucks, so I will be doing this soon.
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Old 02-24-2013, 08:37 PM
CharlesAFerg CharlesAFerg is offline
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Mein Auto: E34 ///M20 2.5i '89
Nope. Like I said, it's not a rattle after start-up, it's a sound during start-up.

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  #5  
Old 02-25-2013, 12:31 AM
Bigrobsbmw Bigrobsbmw is offline
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Mein Auto: 2004 745i, 2001 740i
Seamus by all means upgrade your tensioner but the noise will not go away. I guarantee it is your VANOS gears. Most of these cars do it, and it will keep doiung it until you spend the 500 per side for the gears.
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Old 02-25-2013, 12:36 AM
CharlesAFerg CharlesAFerg is offline
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Mein Auto: E34 ///M20 2.5i '89
Quote:
Originally Posted by Bigrobsbmw View Post
Seamus by all means upgrade your tensioner but the noise will not go away. I guarantee it is your VANOS gears. Most of these cars do it, and it will keep doiung it until you spend the 500 per side for the gears.
Are you talking to Seamus or myself? The sound that my car is making does not sound like VANOS at all.
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Old 02-25-2013, 12:37 AM
Bigrobsbmw Bigrobsbmw is offline
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Mein Auto: 2004 745i, 2001 740i
Charles the only thing I hear is the engine firing prematurely for lack of a better phrase, much like you described. That is not unusual or anything to worry about. Now I did hear something that sounded like a chicken or a dog barking, if that is coming from your engine then there may very well be a problem.
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Old 02-25-2013, 12:38 AM
Bigrobsbmw Bigrobsbmw is offline
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Mein Auto: 2004 745i, 2001 740i
I started the replies with names for direction clarity I thought
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  #9  
Old 02-25-2013, 12:45 AM
Bigrobsbmw Bigrobsbmw is offline
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Mein Auto: 2004 745i, 2001 740i
Does it make the noise on every start ? You are right the air pump has noting to do with that. I think the air pump comes on after the car starts.
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  #10  
Old 02-25-2013, 08:20 PM
CharlesAFerg CharlesAFerg is offline
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Mein Auto: E34 ///M20 2.5i '89
Quote:
Originally Posted by Bigrobsbmw View Post
Charles the only thing I hear is the engine firing prematurely for lack of a better phrase, much like you described. That is not unusual or anything to worry about. Now I did hear something that sounded like a chicken or a dog barking, if that is coming from your engine then there may very well be a problem.
Just a crow.

It does it less when the car is freshly driven hot, but it's not unheard of. It does happen when the car is warm, too. Perhaps even 1-2 hours after it's turned off.
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