Emissions Failure: CO reading

If they were any good they would tell you what was causing the problem by looking at the car, not by plugging a PC in! A real mechanic can diagnose a problem within minutes. Go somewhere else unless they guarantee that their diagnosis will be correct and that the car will pass the MOT if any work they suggest is undertaken. That will make them think twice.

If you gave us the actual figures we might be able to help.

Tim.

Methinks it will make them think once that you're going to be far too much grief to be worth the money.

A real mechanic would know that most cars now are controlled electronically and that a computer diagnostic will give good guideance where the fault lies its no longer possible with many cars to make the adjustments with requards to feuling , timing etc without the use of a computer

if only it was that easy !!! i take it you've not had much dealings with the more modern motor vehicle ?

Reg

Also, why was the cat. converter replaced? Was it physically broken or did the rare metals just perish, fail to function? If the latter, how did you find out?

What is the mileage on the clock? When was the last major full service (as against the in-between minor ones)? Before or after the cat. replacement?

Have you noticed any change in fuel consumption, and in oil consumption? Any unusual (out of the ordinary, irregular) symptoms in cranking, starting, engine warm-up, idle, cruising and acceleration you can tell us? Any illuminated instrument warning indicator light?

And, do you have access to the "Haynes Service & Maintenance Manual" on your car? Here you can find out much besides where the engine diagnostic plug is.

The actual figures are as follows:

Fast idle test: (2365rpm)

CO level =0.75% FAIL HC level =135ppm PASS Lambda=1.03 PASS

2nd fast idle test: (2341rpm)

CO level =0.64% FAIL HC level =117ppm PASS Lambda=1.02 PASS

Natural idle test: (854rpm)

CO level = 0.42%

(Engine oil temp: 83 C)

The cat was replaced in November 2005, following physical damage when the back pipe came undone while driving and the cat suffered damage by being dragged on the road for a short distance. Both back pipe and cat were replaced. Mileage is about 120 000 I changed oil and air filters 1 month ago and spark plugs about 6 months ago. No change in oil or fuel consumption still roughly 45mpg (About 10 miles per litre) and oil seldom needs topping up. No change in driving behaviour of the car. No warning lights illuminated. Yes I have a Haynes manual.

Sure it was warmed up properly? Otherwise from those readings you are looknig at a new cat.

Tim.

"David Linley" wrote in news:en0nco$gpt$ snipped-for-privacy@news6.svr.pol.co.uk:

As we've seen recently, I'm no expert, but......

Your HC level looks high to me, despite it passing. Every emissions report I've seen has shown less than 10 on HC.

AFAIK, Hydrocarbons = unburnt fuel, which should not be in the exhaust even at the pre-CAT stage. Furthermore, I would expect the unburnt fuel to result in a bad (rich) lambda reading. Hence I get the feeling that your lambda sensor is goosed. As the system depends upon the lambda reading to be able to fine tune the mixture, it may also explain why the HC and other problems are there in the first place.

Just my twopenneth, for god's sake don't go out & buy a new sensor on the strength of my incoherent ramblings - wait for a post from someone who knows their stuff!

Stu

illuminated.

Yes, I'm certain it was warmed up properly. I took it for a motorway run on the way to the test.

SO SHUT THE FUCK UP THEN BEFORE YOU MAKE AN ASS OF YOURSELF.

Too late....

Utter rubbish. The only way you'll get them not there is to turn the engine off.

Wrong again. Lambda sensors measure unburned oxygen.

here you go, all about Lambda sensors

Conor wrote in news:MPG.1ffe1181baab04a6989886 @news.karoo.co.uk:

You just don't get it, do you? Unlike your good self, most of us were born without the benefit of infinite knowledge and have to go through what we refer to as 'education'. One way of of doing this is to come up with a theory and then test it to find out if it's correct or not, in this case by posting it on a NG. This is a process that has proven rather effective, since the beginning of time.

Again, you miss the point entirely. What I meant was that the OPs HC result seems rather high to me, because I've seen several MOT emissions results with a variety of cars and have yet to see a HC reading in excess of 10ppm. Care to explain why this could be, while I'm still dousing the flames from your initial post?

That's more like it. A snippet of helpful information amongst the barrage of narrow-minded insults.

Keep smiling, Conor :-)

Stu

Conor wrote in news: snipped-for-privacy@news.karoo.co.uk:

I'm glad for you. Say what you wish, as I refuse to be trolled into a flame war.

Stu

Yes, too much O2 gives a lean reading, too little O2 gives a rich reading.

How was he wrong?

He seemed to think the Lambda Sensor picked up HCs which it doesn't.

David Taylor wrote in news: snipped-for-privacy@outcold.yadt.co.uk:

Exactly. My point was that the hydrocarbon level seems to point at a slightly rich mixture, because it seems a little high to me. And the low oxygen level that results should be indicated by the lambda sensor, which clearly isn't the case.

So, I ask again, is it normal for a modern Efi car to emit in excess of

150ppm hydrocarbons on the MOT test, and if not, is there a possibilty that the lambda sensor is dead?

Stu

Conor wrote in news: snipped-for-privacy@news.karoo.co.uk:

Directly, no. That wasn't what I meant at all. Sorry if it came across that way.

Stu

High HC can be caused by a number of things, incorrect timing, ignition fault, tight valve clearances faulty EGR, inlet manifold air leak, low compression etc. Infact anything that causes the engine to run inefficiently.

150 HC isn't particularly high for a none cat car so if the cat is faulty then that figure is fairly normal.

The OP gave Lambda=1.02 / 1.03 so assuming there is no exhaust leakage the engine is fuelling correctly. With CO at around 0.64% and HC 117ppm (assuming hot engine) then it points to the cat not doing its job.