Failed MOT on lambda, ideas needed please!

[The_blue]

GF's 1.4 k reg just failed on lambda of 16.something.

It had a new exaust sensor about 6 weeks ago due to problems running and engine light comming on and black plugs. I did the paperclip and it said :-

44Oxygen sensorAir/Fuel mixture too lean (weak)


I changed the lambda sensor and power came back and plugs cleared up

Today it failed the MOT on high lambda readings so what could it be? Did i need to reset the ECU after the last fault? if so how?

 

[Dandle]

Could be that something is causing the engine to run dirty which is making the lamda sensor give a bad reading(getting carboned up). What engine is it and is there only one sensor(I would guess there is with it being so old). Have you looked at the engine timing to see if thats ok?

 

[Malachy]

GF's 1.4 k reg just failed on lambda of 16.something.

It had a new exaust sensor about 6 weeks ago due to problems running and engine light comming on and black plugs. I did the paperclip and it said :-

44Oxygen sensorAir/Fuel mixture too lean (weak)


I changed the lambda sensor and power came back and plugs cleared up

Today it failed the MOT on high lambda readings so what could it be? Did i need to reset the ECU after the last fault? if so how?

check the exhaust is not leaking, if its leaking downstream of the sensor it can make the mot testers probe read lean when it really is running fine.