failed mot emissions test

Rich mixture, suspect lambda sensor, but check for misfire too. That's an amazingly high natural idle CO - all but the oldest uncatted cars have to be under 3.5%!

"xtcuk" wrote in news:1140635821.314512.96540 @g43g2000cwa.googlegroups.com:

Your car is running rich. First, make sure the air filter is not clogged with dirt. Assuming it's OK, the fault will be due to a sensor problem or a failed catalytic convertor. The most common cause is a failed oxygen sensor. You will need to get it looked at by an auto electrician to get an accurate diagnosis, as there are several possible causes of the problem.

Not that rich! Dead o2 sensor- about 4% CO max!

Was it properly warmed up? 10mins idling is no where near sufficient!

Tim..

So lamdo 0.93 & CO 2.58% is about right.

I had a similar problem with a 95 Rover 416- kept failing emissions check although not with such a large failure! (5%) My initial thoughts were the Lambda sensor, but thought I'd better get it checked out properly.

After completely changing the filters & plugs, 2 cans of engine flush and lots of swearing, I sent it for a crypton tune. The "technician" (and I use this term VERY loosely) assured me that it was definitely the Catalytic convertor that had gone and would need changed. =A3350 later, with a shiny new Cat fitted, it went back for it's MOT and, funny old thing, failed the emissions test, albeit with a lower CO reading than before.(4.3%) Turned out the problem was the Lambda sensor which cost =A326.95 and took me an hour to fit!!!!

Not that I'm p***ed off or anything.

Craig

Cheers guys for the help.

Just a few things to add:

The message says natural fast idle but i meant to say natural idle.

Another thing they noted was that the fuel pipes where corroded. I don't know if that makes a difference to the CO emissions.

The rear silencer has also just been changed.

We guessed ;-)

No, it wouldn't.

Shouldn't make any difference at all.