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[terry paget]

Yesterday Y188, son Ben's 2.2, passed its MOT test. It failed last year on high lambda reading, which I cured by changing the MAF sensor. This year lambda reading was high again, though less so and descending, but sticking about 1.04. Tester and mate continued with test, discussed the matter, looked for an exhaust leak, found one near the flexi, stuffed it full of Gun-gum sealant, repeated emission test, which it passed.

I am delighted, but puzzled. Was it air leaking in and proceeding upstream to the lambda sensor affecting the reading?

[Kevin Wood]

No. It's not air getting upstream but downstream. The Lambda reading is a calculated value based on the proportion of gases in the (post cat) exhaust flow, indicating what the probable air - fuel ratio might have been in the engine. It is very easily fooled by air being drawn into the exhaust.

When it's outside limits most mechanics will change the lambda sensor as a process of diagnosis by word association rather than looking for a leak!

[Marks DTM Calib]

Absolutely, the engine will be spot on from an 02 perspective but, the air being drawn in at the flexi is fooling the MOT test sensor rammed up the cars arse.

Good news is that the flexi is not to challenging to change out.

[terry paget]

Thank you. Now I understand.

[Varche]

Hey ups Terry. Hats off mate. Another result. I am thinking you are the unsung hero of the forum.

PS what a lucky family you have with you on their spanners.

[frostbite]

I had the same,  where the studs have sheared it's sucking in air.

I had a fail and a pass on the gas analyser the second run had a slightly higher idle speed and it just passed