Lambda level too high

kerryxeg · Post by **kerryxeg** » Mon Oct 29, 2007 8:22 pm

The exige failed its MOT on a high Lambda reading 1.035 actua vs a max of 1.030.

From what I can gather possible things to try are checking for leaks in the exhaust (can't see any probs and would it not fail by more if there were), changing or cleaning spark plugs and cleaning the Lambda sensor. I've looked at the plugs they look fine, but I've got new ones coming anyway. I'm going to remove the sensor tonight, but can you clean it and if so how?

Alterntively might just be easier to replace it, but I'd need to source the sensor tomorrow and leave someone to fit it before the MOT on fri, as I'm away. Part no and supplier in Aberdeen?

Thanks Kerry

Stu160 · Post by **Stu160** » Mon Oct 29, 2007 8:26 pm

Hi Kerry

Also check the coolant temp.sensor,if it fails ,can cause this.

Good luck.

Stu

kerryxeg · Post by **kerryxeg** » Mon Oct 29, 2007 9:38 pm

Th fan still kicks in at the correct temp so I'm guessing that the temp sensor is still working ok.

tenkfeet · Post by **tenkfeet** » Tue Oct 30, 2007 12:54 am

My car failed on lambda last year and the post lambda sensor was u/s reading was 1.179.Was the exhaust really hot , mine failed again but then came good after a thrashing .

This year it was 1.035

after a thrashing for 15 minutes .

robin · Post by **robin** » Tue Oct 30, 2007 9:15 am

S1 exige only has one O2 sensor, pre-cat.

1.035 lambda = 14.7 * 1.035 = 15.2 AFR

I.e. there is too much Oxygen in the exhaust.

Typically caused by air leak into exhaust or failed O2 sensor at the bottom of the manifold.

Could also be caused by failing catalytic converter: If the second part of the catalytic converter has failed (the bit that converts CO -> CO2 and burns partial hydrocarbons to CO2 and water) but the first part is functioning (the bit that converts various oxides of nitrogen into pure nitrogen and oxygen) then you could get an apparent high lambda/AFR.

Air leaks into the exhaust will also make it pop and bang on the overrun.

Failed O2 sensor is easy to diagnose with a multi-meter, but you do need to know what you're doing - the signal should switch between a low voltage (0.2v) and a high voltage (0.8v) about once per second. This demonstrates the operation of the closed loop idle control.

Failed cat may just be lazy cat - suggest you rev the absolute gonads out of it to get the cat good and hot and it may well then pass!

Cheers,
Robin

kerryxeg · Post by **kerryxeg** » Tue Oct 30, 2007 3:52 pm

Thanks robin, the car has been sitting about a bit, so I'm suspecting your lazy cat theory might be the problem. I'll give it a go.

The Cat that is fitted is a "sport Cat" ie free flowing and you can pretty well see through it. I've still got the original, but will it still work properly having sat around in a semi sealed bag for 3 years.

Kerry

robin · Post by **robin** » Tue Oct 30, 2007 4:01 pm

Sports cat - deffo want to get it good and hot - have them rev the arse off it before testing

The other cat maybe OK provided you haven't had it sitting in the cold and damp ...

Cheers,
Robin

YvoTuk · Post by **YvoTuk** » Thu Nov 01, 2007 9:55 pm

echo that, sports cats really want to be hot

Best is to drive the car in anger, come in to the workshop and directly test it.

Beware of the rubber pipe used for the sniffer though, I once had a MOT taken (same procedure, got it VERY hot) and noticed this strange smell.. the rubber hose was completely melted

kerryxeg · Post by **kerryxeg** » Fri Nov 02, 2007 3:21 pm

It passed easily this time, so new plugs, cleaned the lambda sensor and gave the engine a good hard rev before taking it along. One or all of the certainly seemed to work.

Thanks for the comments

Kerry

Stu160 · Post by **Stu160** » Fri Nov 02, 2007 8:48 pm

Result

Stu