Hi Guys,

Stuck my wagon in for its MOT today, passed everything with flying colours (no advisories) except emissions. The Lambda readings are waaaaay cocked.

Results below:

Fast idle test:

CO 5.418 Fail
HC 161 Pass
Lambda 0.888 Fail

Second fast idle test:

CO 0.029 Pass
HC 76 Pass
Lambda 2.621 Fail ???

Natural Idle Test:

CO 0.015 Pass.

So the Lambda goes from rich on the first fast idle, to waaaaaaaaaaaay lean on the second fast idle?

Car runs fine, no misfiring, drives lovely, no CEL. Could it be a dodgy lambda sensor? The readings are crazy.

Cheers

 

REDEX!!

 

I had a fiat punto, where the emissions were too high, got free cat replacement as under warranty but still high, in the end my dad removed air filter for mot worked a treat

I've try Redex and a good service, then loose the air filter make sure cat is hot

 

I don't think thats going to help with a lambda of 2.6

I've bought a new front O2 sensor, its done nearly 77k miles and is 11 years old so could be playing up?

 

Ahh emissions... The bane on my life.

I spent ages trying to get mine through, in the end, found a friendly MOT garage. I replaced front o2 sensor, oil, oil filter, sparks, fuel filter, air filter, got cat up to temperature, ran through redex and cataclean. And it still fails.

My guess is a slight blow in the exhaust somewhere and air is getting in. It's running quite rich I think.
Let me know how you get on. I still haven't managed to fix mine

 

Well below 1 is rich, over 1 is lean. First fast idle it was rich, second fast idle it was lean LOL.

I've got some Firegum to smear over the exhaust joints I've had apart also incase there's a leak. But if it was a leak it would show lean and lean, not rich then lean??

 

Good point mate. I'm not sure myself sounds very strange.

 

Yeah, I don't think it's the cat. It's a prodrive sports cat.

I do still have the stock down pipe. But i'm going to change the O2 sensor first.

 

1. If a vehicle fails for high CO at idle and /or fast idle then.... if Lambda is too low, the mixture is too rich. This can be caused either by a misfire or by a faulty Lambda sensor. If it's running very rich, the 02 and HC will be higher than normal.
2. if it has a high Lambda and high 02 (0.5 to 1.5%), the "CAT" could be faulty. Before condemning it make sure its hot enough to work, the Lambda and other sensors are working OK and the exhaust downpipe hasn't got any leaks.
3. if the vehicle fails for high HC then ...if the CO passes, the vehicle is probably misfiring. Or if the CO fails and the Lambda reading is too low, the mixture is probably too rich and it may also be misfiring.
4. if the CO fails, the Lambda reading is high and the O2 reading is high (0.5 to 1.5%) the "CAT" could be faulty. Again check out the simple measures above before condemning it.
5. if the Lambda fails then...if its too high the Lambda sensor may be faulty, the mixture may be too weak or there may be a hole in the exhaust downpipe. If Lambda is too low the sensor may be faulty, the mixture may be rich or the vehicle may be misfiring.

So mine falls into number 5.

 

I don't even know how a lambda value of 2.6 is even possible. A lambda value of 1.20 converts into an AFR of 17.64 for example. 2.6 the engine wouldn't even run!

 

Been chatting with Duncan (RaceDynamix) about it and it rather smacks of User / MOT Tester error given that the first reading is rich, cats not warm enough, probe comes out, warm car up a bit, incorrectly put probe back in which allows air to get around it and then end up with an epic Lambda value....

I'm going to fit the lambda sensor anyway as I've bought it now and its probably worth doing at the mileage its on, then take it back and get the cat stinking hot on the way, leave the car running and get it straight in to test.

 

Just to update, its now passed its MOT

I replaced the lambda sensor this morning and had a look over the rest of the exhaust, I found a slight blow on one of the weld seams at the lower end of the prodrive sports cat, so smeared some firegum over the seam and that stopped it blowing. Gave it a good run on the way to the test centre to get the temp up and put it straight in.

Lambda was still slightly over at 1.04, but stuffed a rag up the exhaust to seal the probe off and that came down to 1.01 so bang on .