Air Filter

[BMWHacker]

I did a service on the weekend, did the oil, fuel filter and air filter.
The car came with a K&N filter and I've been driving it for about 4 months now without any problems. I'm not a big fan of these filters so I decided to change it to an OEM Mahle filter.

The K&N filter was filthy and looked fit for the bin, so I was fairly sure putting in the new filter would be an improvement.

However, I've noticed since the change that the car now has a flat-spot around 1500-2000 rpm when in 3rd and 4th gear, especially when driving around town. It's also a bit more hesitant when accelerating.
Like I said, I'm not a fan of aftermarket filters, I've tried them before and never noticed any performance gains when using them.
Any one else ever experience this? Is it possible the air filter could make that much difference or did I mess up something else during the service. :smiling:

[Venom]

I did a service on the weekend, did the oil, fuel filter and air filter.
The car came with a K&N filter and I've been driving it for about 4 months now without any problems. I'm not a big fan of these filters so I decided to change it to an OEM Mahle filter.

The K&N filter was filthy and looked fit for the bin, so I was fairly sure putting in the new filter would be an improvement.

However, I've noticed since the change that the car now has a flat-spot around 1500-2000 rpm when in 3rd and 4th gear, especially when driving around town. It's also a bit more hesitant when accelerating.
Like I said, I'm not a fan of aftermarket filters, I've tried them before and never noticed any performance gains when using them.
Any one else ever experience this? Is it possible the air filter could make that much difference or did I mess up something else during the service. :smiling:

what car? Maybe a small vacuum leak? Also worth while cleaning the sensors with electrical contact cleaner.

[BMWHacker]

what car? Maybe a small vacuum leak? Also worth while cleaning the sensors with electrical contact cleaner.

It's an e91 320d with the M47 engine. Yeah I suppose cleaning the MAF sensor can't do any harm.

Refit the old part and see if problem disappears?

Reset the ECU (disconnect battery) to reset the "learn" function?

Check the air intake hoses you moved, they may have been pulled out of place slightly. Or you may have ripped one of the rubbers during installation.

I'll have to go looking in the bin for the old filter. A new one will set me back 80 quid, so that might be the best option if it will fix it.
I wouldn't have thought I'd have to disconnect the battery when changing an air filter, but I suppose it can't do any harm.

Has anybody else ever seen performance gain when using a K&N filter with a diesel Beemer engine? I had one in my old petrol e39 and there was no difference at all.

[Roberto]

I wouldn't have thought I'd have to disconnect the battery when changing an air filter, but I suppose it can't do any harm.

See post 7 in this thread:
http://www.m3forum.net/m3forum/showthread.php?t=226135

[BMWHacker]

I wouldn't have thought I'd have to disconnect the battery when changing an air filter, but I suppose it can't do any harm.

See post 7 in this thread:
http://www.m3forum.net/m3forum/showthread.php?t=226135

So you're saying don't disconnect battery and just drive it like a maniac! :wink:

[Roberto]

Refit the old part and see if problem disappears?

Reset the ECU (disconnect battery) to reset the "learn" function?

Check the air intake hoses you moved, they may have been pulled out of place slightly. Or you may have ripped one of the rubbers during installation.

[Roberto]

I should have included a disclaimer...

[Super4]

Hi there,

Performance air filters on they're own will not give very big performance gains tbh, what they do offer is the following :

Lifetime filter - So in theory it never needs to be changed, just looked after and maintained at regular service intervals.
Less restrictive air flow then ordinary paper filters
Notable improvement in throttle response throughout the rev range
Slight improvements in bhp and torque when combined with other modifications.

The better your engine can breath, then the better it shall perform. Performance panel filters need to be maintained properly in order for them to last as long as they are designed to. If a filter is let get to an exceptionally poor state then naturally it shall not be able to perform as well as it should, however in some cases it may still outperform the ordinary paper filter. If you are planning to go back down the route of a performance panel filter then drop me a PM when time comes and I can get you sorted out with a "GREEN Performance" replacement air filter. I have personally been using these and supplying them to customers for quite some time and tbh I find them very hard to beat. They have proven to notably increase throttle response on all applications and to date customers seem to be very happy with them.

On another note, as mentioned above do go back over your work to make sure all the vacuum and breather pipes are fastened down and securely and refitted properly.


Hope this helps,