MOT failed on lambda

[blueleon]

I failed, well the car failed its mot for the first time thing is every time the car has had an mot its always been close but normally passes here are the figures;

fast idle

CO: <=0.200% 0.028% PASS
HC: <=200ppm 8 ppm PASS
LAMBDA 0.970-1.030 1.725 FAIL

Second fast idle

CO: <=0.200% 0.014% PASS
HC: <=200ppm 9 ppm PASS
LAMBDA 0.970-1.030 1.666 FAIL

added some fuel cleaner took the car for some spirited driving and so it was nice and hot still failed. My car has been mapped and has a typhoon induction kit other than that its standard or and it has a powerflow exhaust. Its been like that for years and has normally passed though.

What will make it pass?

The garage recommend a new cat although I thought a new lambda sensor. if I choose a cat will a 200 cell sports and 3" downpipe work better, emissions wise that is.

 

[blueleon]

that's true my car has always been near the limit to pass from the day i got it. Is there a way to check the cat is working or not other than emission tests? I hate to waste money on something I don't need. Thanks

 

[mty12345]

i would imagine with the reading that far out of spec it must be the sensor or an airleak in the exhaust BEFORE the sensor, if it was the cat the other readings would be higher as well: this might help you out.....


If the fault is a high lambda reading, with a high O2 reading but with normal CO and HC readings, the most common cause is post combustion air leaks. A small exhaust system air leak will leak air into the exhaust before any blows can be detected. Only a small volume of clean air introduced into the exhaust will cause a car to fail the MOT test.
Various manufactures have had their problems with exhaust air leaks. The Ford Mondeo is a notable example, with various modifications to the manifold sealing ring having been carried out to p revent such an occurrence. Other cars such as Nissans are fitted with a drain hole in the rear silencer. You may need to temporarily bung this drain hole up to prevent a MOT failure. Check these first before condemning or even checking other emission parts.
An air leak after the lambda sensor, i.e. exhaust silencer/joint etc leak, will cause the O2 reading to be high and all the rest to be normal. If the air leak is before the lambda sensor, i.e. manifold/ down pipe, then a diluted exhaust gas will be monitored by the lambda.

 

[blueleon]

Some sound advice from you thanks I'll take this on board, why can mechanics not do these checks. I've found most places just want to replace rather than repair, I real mechanic is skilled most I think take the easy option and replace items. Thanks again people I will take the car to an exhaust place and get them to check it out.

 

[blueleon]

What a pain took the car to another garage for a second opinion and they think the same, it doesn't look like the cat from looking at the readings. They checked the exhaust and told me it blowing just a bit but that would not make the reading that high. MOT bays were full until next week so he couldn't test it. ( he made a comment that because the exhaust is big it could have an effect by sucking some air in and they sometimes stick a rag in).

Took the car to veedubs for a diagnostics and he couldn't find any issues with lambda sensor or anything.

Thing is I cleared a code the other day 16804 which could be a cat or a sensor.

Took the car back for a retest armed with all the other info I gathered it still failed and the still think it needs a new cat!

Should I buy a new cat and keep my fingers crossed or what.?

Your advice needed please

 

[mty12345]

soz to hear bout latest outcome, it still seems strange to me that the cat would give a reading so far out of spec. The big exhaust theory sounds bout right though, don't think the car would run with a lambda reading that lean, so is it possible the first garage either didn't have the probe in far enough or like the mechanic said, maybe air was being drawn over the sensor from the tail-pipe end and messing up the reading? What does everyone else think?

 

[mty12345]

bump

 

[blueleon]

Thanks mty12345, for your response

I am happy to buy a new cat if it resolves the issue, been telling pork pies to me lass that a sports cat will last forever but if i buy one and it still doesn't pass I'll be in bother. come guys and girls.

 

[mty12345]

 

[wayne n]

Not really my field of expertise but my old manager used to work for bosal and told me if something has killed the cat and you fit another that will also die. Told me exhaust paste will kill them cos of the silicone or oil leaks are also a fav. May be a bit off top pic but just my 2P.
Hope you get it sorted. what you been quoted for a new cat?

 

[blueleon]

thanks your right I do need to find out what has ruined the cat first, they quoted me like £600 ish I think, I switched off when they said I need a new cat, thinking this was a good time to upgrade.

Sensible head back I dont want to jump in with both feet wasting cash on a sports cat if thats going to be ruined too.

 

[OVNIWCE]

If the fault is a high lambda reading, with a high O2 reading but with normal CO and HC readings, the most common cause is post combustion air leaks. A small exhaust system air leak will leak air into the exhaust before any blows can be detected. Only a small volume of clean air introduced into the exhaust will cause a car to fail the mot.

 

[mty12345]

sorry to see you've still had no more help on here yet buddy, u had any more developments with it today?

 

[blueleon]

Hi thanks for posting again, Na cars parked on the yard at the minute I'll get to it at the weekend. I can get the car MOT'ed anytime but I'd rather have it all done properly and know what the real issue is. I did find out that the cat which is on the car not does not seem to be a genuine part Its been on the car since I bought it at 20k miles so maybe it had a decat on before and the garage put a cheapo cat on who knows, I'll see what the weekend brings.

 

[blueleon]

I'm thinking with the winter coming I may keep the car of the road and sort out all the small issues leaky injector seats and the cam cover gasket has a small leak too so i'll sort that and paint it whilst its off. The car is really bad in the snow anyway so maybe a blessing