BMW 320D Swirl Flaps

Wikipaedia article on Swirl Flaps

Just read an interesting article on swirl flaps on Wikipaedia that can be found here. According to this article the primary purpose is to introduce turbulence into the inlet manifold with the end result of reducing harmful emissions. It also suggests that they have a minor impact on fuel consumption but I can report otherwise!

Fuel economy drastically improved on urban driving

Fuel economy is drastically improved even on urban driving. The author of the article probably meant that the swirl flaps weren't an economy device as such and the improvement I'm experiencing is principally due to a happier ECU.

One disadvantage - Smoke on acceleration

Important to say that one effect of disconnecting the flaps is heavy smoking on hard acceleration at low revs. At times it's really heavy smoke.

BMW 320D erratic performance problem solved!

Finally, after all these months I've identified the cause of the poor performance. Swirl flaps.

Replacement MAF and EGR resulted in misleading improvements

The symptoms started well over a year ago and resulted in me replacing the MAF and EGR valve. This misleadingly produced an initial improvements but the symptoms gradually came back and were backed up by the ECU light indicating an obscure P3263 fault. Diagnostics by the dealer and various technicians could only suggest an air flow problem which resulted in the MAF and EGR replacements.

Swirl flaps influence air flow as well

Of course there is one more component that can interfere with the air flow. The swirl flaps! Isn't hind sight a wonderful thing because it now seems such an obvious thing to check. That said I am and was a little apprehensive about the consequences of disconnecting components so this did deter me. When I did decide to disable the flaps it took mere seconds to pull off the vacuum pipe and block it off.

Fuel economy drastically improved to 60mpg on the motorway

The result was the ECU light immediately went out. The flat spots and lack of power disappeared and fuel consumption improved drastically. From a best of just over 50mpg with the faulty flaps to over 60mpg with them disconnected. That's better than I've ever achieved even when I bought the car at 3 years old. So have they been interfering all the time!?

To carry out further investigation of air flow vs RPM 

I'm intrigued at the impact the swirl flaps have on performance so I hope to use my Torque app to carry out some more measurements of air flow versus engine rpm. I wonder if they will show a much cleaner correlation than the ones I took initially?