How excessive are these MOT emissions figures? (Clio 172)

Cash-Strapped.T32

Hi, hoping for some down to earth advice here.
Car failed its MOT today - I took it in on the earliest date I could, so I'd have a bit of time to sort anything that cropped up - turns out the emissions test did it.


It's a Clio 172, 53 plate on about 160k miles.
On the first fast idle, taken at 2700rpm;

CO MIN = 0   |   CO MAX = 0.3   |   CO ACTUAL = 0    -PASS
HC MIN = 0   |   HC MAX = 200   |   HC ACTUAL = 7    -PASS
LAMBDA MIN = 0.970 | MAX = 1.030 | ACTUAL 1.037      -FAIL

Second test;

CO MIN = 0   |   CO MAX = 0.3   |   CO ACTUAL = 0     -PASS
HC MIN = 0   |   HC MAX = 200   |   HC ACTUAL = 7     -PASS
LAMBDA MIN = 0.970 | MAX = 1.030 | ACTUAL 1.032      -FAIL

The second test is very similar, only the final lamda value changed, going down from 1.037 to 1.032.

My question is, how bad is this result? And what would I be hoping to achieve?
I'm guessing the CO refers to CO2, HC refers to Hydrocarbons, and the Lamba refers to the rich or lean fuel mix?


I've gone over one or two previous threads, and I intend to get the oil & filters changed (last done in Feb, just before the snow), replace the cone-filter the car came with, with a second hand oem airbox & paper filter (it's never bothered me before so left it in place), perhaps replace the plugs and run a bottle of redex or two through it, but does anyone have any further advice, given the results above?


Thanks all - I'd hate to scrap a lovely little car over what looks like a fration of a decimal place, but I'm not well-up on emissions readings so not entirely sure what I'm looking at.
Cheers!

facade

The high lambda means a weak mixture.
If it were running lean it would likely missfire, and the unburnt fuel would put the HC up, so I'd say it is running fine.


Most likely there is a hole in the exhaust somewhere and it is drawing in extra air.

EdGasketTheSecond

A slight exhaust leak will put the lambda reading high. Most likely the back box or join with the back box has a leak. See if you can feel it puffing anywhere around those with the engine idling.

reeac

The CO represents carbon monoxide, not dioxide. I've never seen a zero for CO on any of my cars but it would be consistent with a high lamda i.e. excess oxygen drawn in leading to complete combustion of CO to CO2. Can't offer any remedy but to search the Internet.

AdrianC

Start by changing the lambda sensor, if there's no exhaust leak.

Cash-Strapped.T32

Thanks very much lads :beer:
Ok, so first step, get it up on ramps & see if it's obviously leaking air.
The workshop at work replaced the back box a couple of months back, so I guess that could have introduced a leak to the system were it not fited correctly - I also have a spare mid-section pipe in the shed in case that turns out to be holed...



Do we think the slightly boy-raceresque induction kit & cone filter could cause such a leak?
In fairness to the chavette who fitted it prior to me having the car, the installation seems rock solid, no movement or obvious leaks, but you never know - it seems logical?
I was considering getting a 2nd hand airbox & new paper filter... Worth looking at?

If that fails, lambda sensors (it has two).
Bah, they're not cheap are they?

I'm also going to budget for a change of oil & oil filter - does that seem like a waste since they were only changed about 6 months ago?

Thanks so far everyone - I intend to keep updating this as we go on & it either passes or fails for good - god help me!

AdrianC

No, the naff boy racer filter won't have caused the problem. The whole job of the lambda/oxygen sensor is to tell the ECU whether the engine is running too lean (too much oxygen) or too rich (too little), and adjust the fuelling to compensate.

The MOT measures the lambda at the tailpipe, the ECU at the sensor near to the manifold.

Lambda more than 1.00 is too lean, too much air, too little fuel.

facade

AdrianC wrote: »

The MOT measures the lambda at the tailpipe, the ECU at the sensor near to the manifold.

Lambda more than 1.00 is too lean, too much air, too little fuel.

So any leak in the exhaust between that manifold sensor and the tailpipe will let in extra air, and push the lambda over 1.00, whilst the engine is fuelling perfectly.


If the CO is zero, then likely the leak is a split seam on the catalyst, as the extra oxygen is allowing the catalyst to fully convert CO to CO2
If the CO is pass but small, the leak is after the catalyst.


If there are definitely no leaks, then the manifold sensor may have worn out, and be sending the wrong signal to the ecu, which makes it set a weak mixture.

Cash-Strapped.T32

Ok, so shock horror - turned out to be an air leak, introduced when the exhaust was replaced.. (I bet nobody saw that coming!)

Long story short, when I took the car to the little garage just down the road from our work a couple of months back, they had the new lad (first job he'd done for them) replace my pipe - no problem I thought, it's just a bolt-on job and to be fair, they're normally pretty damn good to us as we send a lot of business thier way.

I supplied them with the replacement mid-section and back-box, however only the mid section was replaced, as the lad didn't think the backbox was in a bad state - and to be fair, I didn't worry as I knew it would get used sooner or later down the line.

However what I didn't know is that the bore was totally different between the current backbox & new mid section, leaving a pretty decent gap all around (no paste used either - hell, I'm almost suprprised he didn't try to crimp it with some molegrips or something)

So we had it up on ramps today, found this gap and fitted the backbox that I'd been keeping in the boot - ran it though the machine, and emissions now read;

    CO ACTUAL = 0 
    HC ACTUAL = 3 
LAMBDA ACTUAL = 1.011

Which seems much more healthy. :cool:

Going to put it in for the retest tomorrow - looking good, although I'm still not entirely sure why my CO is reading zero..

I'm still going to do a fuild & filter change, plus replace the plugs & leads before christmas but just for regular maintenance, not as a fire-fighting measure.

Anyway, just wanted to put update this out there to let you know how it went, but also for anyone who is reading this out of idle curiosity, to reinforce the fact that with some common sense and reasoning it should be possible to figure out the area that wants looking at before you start chucking silly money at a problem...

I'll freely admit that before this, the numbers that make up your emissions values were pretty much a closed box to me, but thanks to the guys on here I've started to see the logic behind it - and once you begin to understand why a thing is, you can begin to assert control over it, rather than the other way round.
Cheers lads! :beer:

AdrianC

Cash-Strapped.T32 wrote: »

although I'm still not entirely sure why my CO is reading zero..

Because one of the jobs of a cat is to oxidise CO into CO2.


You can't "gas" yourself in a catted car... Do you know how many times I've shouted that at Midsomer Murders and the like...?