Ford Fiesta - Fiesta MOT fail for high "Lambda"

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Sat 20 Nov 2010 21:30
Ford Fiesta - Fiesta MOT fail for high "Lambda" - p0l0nium

Thought I'd add this to the "Sum of human knowledge".

My 1999 1.25 fiesta zetec failed MOT for high "Lambda" (1.059 against a spec of 0.97 to 1.03). "MOT guy" suggested I fix the small leak in the end exhaust box and bring it back for retest.

So I plugged the leak and he was right - it now measures 0.997 (supposed to be 1.000)

It turns out that the "emissions" test isn't testing what the car "emits". It tests what it sucks in through small (non MOT failing) leaks.

High "Lambda", apparently, is supposed to be a sign of excessively weak mixture or incomplete combustion (high oxygen content in the exhaust gas).

So , if your car fails MOT for "Lambda" don't let some grease-monkey sell you a "Lambda Sensor" unless you know its defective.

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Sun 21 Nov 2010 10:31
Ford Fiesta - Fiesta MOT fail for high "Lambda" - injection doc

your quite right and sometimes the smallest of air leaks in the exhaust or the sample pipe of the gas analyser can cause high lambda. Every morning a gas analyzer has to be put through a leak check before MOT testing but they can have such a tiny leak that it goes un-detected! Another classic is if the sample hose is not inserted far enough up the exhaust.

There are many causes of high lambda and the sensor is not the first port of call

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