Hi,

I have a Ford Fiesta Flame which just failed it's MOT with a high lambda reading and not really sure why.

I drove the car their in lower gears than normal as I've heard this helps.

I have recently had a new Cat and Exhaust fitted didn't replace the lambda sensors.

Spark Plugs were done recently.

The MOT reading was fluctuating and not far off passing.

I have checked for any leaks in the exhaust which there are none to my knowledge.

Any pointers on what could cause this would be appreciated.

thanks

What was the lambda reading? , or was it going high and low, why was the cat replaced recently,

Engine Management Light came on last year, took it to a garage and they said it was the Cat that needed replacing. The engine management light has not come on since.

It was fluctuating but never went under 1.031

The garage said to buy some cat cleaner and try again. Given the age of the cat I am a little reluctant to do this, the car mainly does short trips though?

Not really sure what to do and the garage didn't seem to know either :(

Thanks again.

High lambda has nothing to do with the condition of cat, high readings normally either leak in exhuast drawing air in weaking the measured gases at probe, or alernatively the lambda sensor not regulating the air fuel ratio acuratly.( sensor reads gases as too rich and weakens the fuel mixture giving high lambda)

the co and hc passed ok?

They were fine just the lambda reading.

I had some Redex petrol Injector Cleaner kicking around, I have put this in after it failed.

Would the cat cleaner do anything for the lambda reading?

it may clean the sensor, never used it so not sure. poor garage who cant diagnose it, needs the sensor checking while running on an ociliscope to check its switching properly or not

They are not the cheapest either, I thought the same when I asked what would be causing the high reading.

I will try the Cat cleaner and then take it for it's retest as getting quite desperate, will look into local garages which can check the sensor and probably a service.

I have stuck with the same garage for eight years mainly because of the fear factor of going to another.

thanks,

Engine Management Light came on last year, took it to a garage and they said it was the Cat that needed replacing. The engine management light has not come on since.

It was fluctuating but never went under 1.031

The garage said to buy some cat cleaner and try again. Given the age of the cat I am a little reluctant to do this, the car mainly does short trips though?

Not really sure what to do and the garage didn't seem to know either :(

This garage that you took it to, they did actually replace the cat, or did they do something else?

In any case, your lambda reading isn't far off, and you might get lucky with some marginal treatment (mostly, when cars fail, there is a fault that puts them further off than this). Close, but no cigar... Anyway, was the car thoroughly warmed up when they tested it? That does make a difference, although usually if the car fails by a small margin, a sensible garage will leave the car running for a while to see if it improves.

What is the idle speed doing? Is it stable and is it at its usual value? Has anyone checked that the Lambda sensor heaters are working?