MOT Failure

[mr angry]

I know this has been discussed before and have spent an hour searching.
I have a 53 172 33000 miles and it has just failed emissions miserably. There seems to be varying opinions as to whether the pre or post O2 sensor is usually at fault.
Any educated views are appreciated and if you have one for sale I am interested.

 

[BSC 182]

The voltage reading from the lambda sensor is often a very good place to start with your diagnose of an emissions failure fault. The lambda sensor can be used as a pre-cat emission tester when used with either an accurate voltmeter or an oscilloscope. With the engine up-to normal working temperature, check the output of the sensor wire, normally black with Zirconia sensors, you should expect an output of 0.2 – 0.8 volts fluctuating between these reading approximately 2 – 3 times per second. If the output voltage is lower than this, i.e. 0 – 0.2 volts there will be a lean running or excess oxygen problem. If the voltage is higher than this, i.e. 0.8 – 1.2 volts then there will be a rich running or excess fuel fault .

 

[stooby]

take it to a 'special' mot place where they test a different cars emissions
a 'friend' has a straight thru decat pipe and when he has his mot done they very kindly do that for him..

 

[lemonnobby]

Make sure it was really warm when the test was done. renault have a habit of failing if cold.

 

[16v_jon]

Take it out rag the shite out of it make sure there is super in the tank and when its nice and hot get them to test it.

 

[mr angry]

Ok, all fixed. Replaced the upstream sensor and its fine. GSF £54 + vat. Its like a new car again what a difference in performance its been sluggish for a while now.