Knocking coming from out back...

K

kerph32

Member
#1
Messages
163
Likes
0
Location
Atlanta
#1
Under hard acceleration I hear a kind of knocking noise that appears to come from the rear-right side of the car. I use mid-grade fuel... is that my problem? I'm not sure if this is the same "knocking" that people talk about when talking about using too low of a grade of fuel.
Thanks for any help
Mike
 
K

kerph32

Member
#2
Messages
163
Likes
0
Location
Atlanta
#2
anyone? maybe I should call the dealer... they'd probably just be like, 'well bring it in, we'll charge you $100 to have a mechanic ride with you to determine the problem.'... ugh dealers suck
 
C

CTBMW

Member
#3
Messages
247
Likes
0
Location
S.E. CT.
#3
You really should be using 93 octane. The "knocking" you would hear using a lower octane is usually pinging sound if I remember from years gone by and I think it was more towards engine.
You hear it on right rear, exhaust is left rear?
I'm thinking out loud..
It seems like too low octane would be felt/ heard up front or out tail pipi under a load (accelerating, going up a hill, lugging engine)
Could something be loose? Does it happen all the time?
Why on earth would you go to the dealer?! They are SOOO expensive! No good BMW shops around you?
Wish you the best-let us know how you make out! (you may help someone else out)
-Mel
 
K

kerph32

Member
#4
Messages
163
Likes
0
Location
Atlanta
#4
It only happens under hard acceleration... I just moved here to Knoxville (UT) so I haven't had a chance to look for any BMW shops, I'm sure there are plenty. I just have to find them :)
Thanks for your help! I'll think about the octane thing... is it just unhealthy for the engine to use 89?
 
skandalous

skandalous

2
#5
Messages
526
Likes
0
Location
Nashville, Tn/Baton Rouge, LA
#5
In Knoxville the only dealer I'm familiar with is Grayson BMW. I don't quite remember where it is. And yes, 89 octane is unhealthy for the car. Use premium gas, unless you use a fuel additive, but even then I still use premium.

Also, sorry to here you go to UT. [;)]
 
E

epj3

Senior Member
#6
Messages
7,370
Likes
0
Location
Lancaster, PA
#6
It has nothing to do with gasoline, why would that effect the REAR of the car, unless it was the tank itself?!?

It's most likely something loose or worn out, IE exhaust/suspension/etc. Or the most likely thing is your driveshaft center support bearing and Guibo (flex disk) need replaced. This is a very very common part to be replaced on bmw's. Sometimes the flex disk only lasts 25k miles [rolleyes]
 
E

epj3

Senior Member
#8
Messages
7,370
Likes
0
Location
Lancaster, PA
#8
CTBMW said:
You really should be using 93 octane. The "knocking" you would hear using a lower octane is usually pinging sound if I remember from years gone by and I think it was more towards engine.
You hear it on right rear, exhaust is left rear?
I'm thinking out loud..
It seems like too low octane would be felt/ heard up front or out tail pipi under a load (accelerating, going up a hill, lugging engine)
Could something be loose? Does it happen all the time?
Why on earth would you go to the dealer?! They are SOOO expensive! No good BMW shops around you?
Wish you the best-let us know how you make out! (you may help someone else out)
-Mel
Click to expand...
The knocking is to do with the valves, so you would not hear it out the exhaust.
 
Steve Neu

Steve Neu

Member
#9
Messages
39
Likes
0
Location
San Diego
#9
epj3 said:
The knocking is to do with the valves, so you would not hear it out the exhaust.
Click to expand...
Nope--it is caused by pre-ignition of the fuel/air charge which can be a result of hotspots in the combustion chamber-- which can be caused by deposits.

The strange ideas aboutgasoline octane and power leads me to believe that many BMW owners are appliance operators and not really up on how their cars work! :)

Steve
 
E

epj3

Senior Member
#10
Messages
7,370
Likes
0
Location
Lancaster, PA
#10
Steve Neu said:
Nope--it is caused by pre-ignition of the fuel/air charge which can be a result of hotspots in the combustion chamber-- which can be caused by deposits.

The strange ideas aboutgasoline octane and power leads me to believe that many BMW owners are appliance operators and not really up on how their cars work! :)

Steve
Click to expand...
Ah thanks, but I still dont think it would be noticeable out of the exhaust, it would be up in the front if anything.
 
Steve Neu

Steve Neu

Member
#12
Messages
39
Likes
0
Location
San Diego
#12
Pre-ignition or knocking usually has a metalic tinny sound to it. It would be from the engine--not the back of the car.

In any event BMWs have had knock sensors that detect pre-ignition and retard the timing long before you can hear it. Knocking is rare even with 87 octane with knock sensors.

Steve
 
E

epj3

Senior Member
#13
Messages
7,370
Likes
0
Location
Lancaster, PA
#13
That's what I thought Steve. They were saying it might come from the exhaust, which the only 'knocking' noise i've heard from the exhaust is a backfire -- and i've never heard a bmw backfire in my life. I'd strongly suggest checking the Guibo, it might be in rough shape.
 
You must log in or register to reply here.


Top