Car just failed it's MOT on emmisions.

According to the Diagnostics the CAT is ineffeciant.
Now It had a new CAT 2 years ago so I think it's the Post Cat O2 sensor.

I'm going to change the Pre and Post CAT O2 sensors.
Could it be anything else?
Bailes.

 

What fault codes does it show?

If it's P0141 it's a hego sensor (lambda) heater circuit failure. If cat is inefficient it'll show a P0420, Ideally needs both sensors data logging to see if the output voltage from the post cat sensor mirrors the pre cat sensor output voltage. If cat and post cat sensor are good the output voltage of post cat sensor should be constant, not switching between 0.2 -0.8 volts when in closed loop.

 

It's showing P0420. Im thinking that the front Lambda is worn causing it to overfuel which the He-Go sensor is picking up on and saying the Cat is Inefficiant?
Already got the PreCat Lambda, will get a rear one straight from ford at £164
Get them both changed and see if it goes through.

 

We used to get a lot of P0420s show up on Fiesta/Focus shortly after they had been in for a misfire (coil pack etc) especially if customers had been driving about for ages with said misfire..

Normally a new CAT will solve it as long as the sensors are working properly of course. As said above I datalog on IDS both pre and post cat sensors to determine if it's a sensor or a cat.

 

i wouldnt buy direct from ford just get a bosch sensor from one of the motor factors as the are as good as if not exceeding oe quality (most oe sensors are bosch anyway) and will only cost around £40

 

As above get a bosch sensor just as good as ford, my pre cat sensor just cost me £75

 

Already had a Precat sensor. Had it fitted today after a Dyno showed my cars fueling was all over the place. Car is driving 10 million times better! Not hesitant, dosen't bog down, pulls itself along on the clutch etc etc

84.9bhp and 90.7FtLb at the Wheels
106.4 at the fly

 

Guys I'm at a loss...
What would cause high Carbon monoxide levels?
The first MOT the Lambda was around 1.016, so I replaced the lambda. Now it's running dead on 1.000 and I'm still failing on Carbon monoxide?

 

Pointing towards a fooked cat.

If you had a lambda fault or a rich or lean mixture the Lambda reading would not pass

(low lambda = rich , high lambda = lean)

Seeing you had a P0420 code, it points toward a cat being ineffective.

 

Booked in Friday for a new CAT. It's only 2 years old too

 

My genuine Ford pre cat lambda was cheaper than that!

 

Ford want £164 for a Precat Lambda!
I paid £29.99 for mine and £25 fitting. The new lambda brought the Lambda down from 1.016 to 0.999/1.000.
But still failing on CO so booked in for a CAT on Friday.

 

yours is different to an st170 though...