Emissions & squeak

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spudey - 03 Jul 2003 02:51 GMT

Hey folks, My '97 Cooper (Mpi) failed the MOT today on emissions.

Passed the natural idle test, but failed both fast idle tests because of the
lambda reading (CO and HC were fine)

At 2846 rpm lambda was 1.152 (limits are 0.950 - 1.090)
at 2764 rpm lambda was 1.146.

Does anyone have any suggestions before i get my hands dirty later today? I
was thinking along the lines of the downpipe not being sealed properly,
because i fitted an lcb last august. all runs/sounds ok though.

Also have a squeak coming from near the driver's footwell, above the pedals
when the car is moving (engine on or off). sounds like a plasticy kind of
rubbing, kind of random but persistant. hard to describe. checked steering
rack and looked in the airbox for mice :o)

Any ideas? or am i going to have to listen to the radio all day?

Cheers,
SPUDEY.

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Revlac - 04 Jul 2003 18:26 GMT

High lambda is usually a leak in the exhaust pipe downstream of the cat.....

> Hey folks, My '97 Cooper (Mpi) failed the MOT today on emissions.
>
[quoted text clipped - 17 lines]
> Cheers,
> SPUDEY.

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Graham - 07 Jul 2003 04:04 GMT

Revlac wrote:

> High lambda is usually a leak in the exhaust pipe downstream of the
> cat.....

How does a leak in the exhaust downstream of the cat, which is itself
downstream of the oxygen sensor, affect the composition of the gases at
the oxygen sensor?

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xsplam - 07 Jul 2003 07:43 GMT

Graham <zebedee@alphalink.com.au> wrote in news:3F08E32F.71498030
@alphalink.com.au:

> Revlac wrote:
>> High lambda is usually a leak in the exhaust pipe downstream of the
[quoted text clipped - 3 lines]
> downstream of the oxygen sensor, affect the composition of the gases at
> the oxygen sensor?

Perhaps there's a disruption of exhaust flow causing an increase of
backpressure?
No idea really, but I'm always happy to guess! weee

splam

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Graham - 08 Jul 2003 09:08 GMT

> >> High lambda is usually a leak in the exhaust pipe downstream of
> >> the cat.....

> > How does a leak in the exhaust downstream of the cat, which is
> > itself downstream of the oxygen sensor, affect the composition of
> > the gases at the oxygen sensor?

> Perhaps there's a disruption of exhaust flow causing an increase of
> backpressure?

You'd expect to see a reduction in exhaust back pressure with any leak
in the exhaust. But a leak out beyonf the cat is not going to directly
affect the composition of the exhaust gases at the motor and should not
affect the mixture so badly that the injection system won't correct for
it based on the lambda sensor output.

> No idea really, but I'm always happy to guess! weee

Sadly, guessing is what I suspect Revlac was doing, which just leads
people astray. Bad advice is worse than no advice.

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