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MG MGF Technical - K&N Induction Kit and MOT emission test

My F (98 VVC, 76K miles) has just been through its MOT. Just before the MOT I had a K&N fitted. Only the MOT centre had to remove it because it failed the emission test.

When trying the fast idle test...

The CO level with the K&N fitted was recorded as: 0.54%

The CO level with the standard filter was recorded as: 0.06%

The threshhold for passing is: 0.20%

So, my question is simple... Why would this be?

Is this a problem that others have had? The filter was cleaned before fitting, I assume satisfactorily.

While I am here, how do the figures below match with folks out there...

Fast idle speed CO level - 0.06%
Natural idle speed CO level - 0.09%
HC level - 45ppm

d.
d.

As far as I am concerned the air filter should not affect emissions as all it does is feed air in to the throttle body. The onlt difference between a K&N and std filter is it allows the engine to have a better suppy of air to the engine.

I have never had problems with emissions at MOT and these have been with both K&N and ITG.

Tom
Tom Randell

Fast idle
CO Level 0.05
HC Level 14 ppm
no idle test

That was on a VVC with freshly cleaned K&N.

Never had a problem in 5 MoT tests - you have something strange going on!

Cheers

Patrick
PA Beet

It could be that the car was warmer when tested with the standard filter in place.

Sam
Sam Murray

Interesting...I had a similar experience with a local garage who said the K&N was affecting the emissions and failed it.
So I took it to the MGFC. They diagnosed a knackered cat, put me a second hand one on and it passed the MOT !!
Out of interest, does the car have to have an airfilter connected to go through the MOT ??
Carl Lambert

How soon before the MoT did you fit the K&N?

At idle, the engine managment is in 'closed loop' feedback mode, which basically means that the engine management is altering the air:fuel ration to optimise emissions.

I wonder whether the IACV was compensating correctly for the new airfilter?
Rob Bell

The filter was fitted a few days before the MOT, but it certainly wasn't 'run in'.

Would the IACV operate differently with a new filter? What controls the IACV?

Do you think a wee run would have helped? :)
d.

The IACV will have to operate differently with a new airfilter to compensate for the altered air flow characteristics (i.e. the new filter will flow considerably more air than a paper element, especially if it is dirty). The IACV is modulated by the engine mangement system (MEMS), that adapts to altered operating environments.

I guess it is possible that the MEMS hadn't adapted to the new filter characteristics. I would have expected it to run lean though, not rich - but perhaps this is a sign of over-compensation?
Rob Bell

Rob,

I had a similar issue at my last 2 MOT's with the K&N also :o( thankfully the tester took it for a quick run and the immissions dropped (just below the level). The K&N had been installed for 2 years. The car itself runs fine and has been serviced by TS. Was a bit concerned about it though, with the new remote testing stations being setup as it takes limits the testers options, especially if he can't retest on the same day. Remote analysis of the MOT's however should standardise the results though :)

Les

Les

Thanks guys, your comments are much appreciated.

I will see about getting it fitted again, take it for a decent spin, and see if I can get the emissions tested again.

d.

PS: There's something less than satisfactory about the new MOT certificates. Don't feel as legitimate... :)
d.

This thread was discussed on 13/07/2005

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