MOT - Fail 8.2.1.2 (c)

[Reece Newell]

Hello all

Need some help, my younger brothers Starlet has failed its MOT on the O2 sensor reading too much oxygen, 1.23 on its first test, 1.18 on its retest. the limits are 0.97-1.03

i have given the car a full engine service i.e - oil, oil filter, air filter, fuel filter, spark plugs, and i had fitted new O2 sensor as the cars only done 55k miles but i figured the O2 sensor might be the original one fitted and ran injetor cleaner additive before mot re-test incase the injectors were abit gummed up, car runs great tho? but sadly it still failed the retest, its a EP91 1998 1.3 Starlet, everything is standard but we did fit a cherry bomb in place of the rear silencer, didnt think this would be the issue due to there being a cat and centre silencer after the O2 sesnor location.

please let me know your thoughts it didnt fail its last MOT and the only thing thats changed really is the cherry bomb fitted to the exhaust

 

Thanks - Reece 

[Claymore]

As far as I understand the emissions test a high lambda reading usually indicates an exhaust leak letting in air (oxygen) and it then shows up on the MOT testers O2 sensor in the exhaust pipe tip where they take the reading.

I'd check the exhaust for leaks at all the joints, (especially the new back box) and also for holes in the pipes.

Could be the engine genuinely running lean, but the other readings should show that.

Edited April 6, 2022 by Claymore

[Reece Newell]

1 hour ago, Claymore said:

As far as I understand the emissions test a high lambda reading usually indicates an exhaust leak letting in air (oxygen) and it then shows up on the MOT testers O2 sensor in the exhaust pipe tip where they take the reading.

I'd check the exhaust for leaks at all the joints, (especially the new back box) and also for holes in the pipes.

Could be the engine genuinely running lean, but the other readings should show that.

Thanks Claymore, ill have a check over the weekend for leaks, it might well be what we disturbed when changing the cherry bomb over, as it passed on everything else but the O2 sensor being out of the limits