 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Car Forum / UK Car Forums / Car Maintenance (UK group) / December 2006Emissions Failure: CO reading
My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other emissions readings were within tolerance. The MOT tester seemed to think this was the CAT, but that was only replaced in November 2005. What are the other likely culprits for a higher than legal CO reading? Lambda sensor? ECU? Something else? My nearest garage has offered to perform a diagnostic test for £35 + VAT with a computer or £45 + VAT if a manual inspection is necessary. I make that about £42 and about £53 in real money. Is this a reasonable price? David. > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other > emissions readings were within tolerance. The MOT tester seemed to think [quoted text clipped - 10 lines] > > David. 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. >> My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other >> emissions readings were within tolerance. The MOT tester seemed to think [quoted text clipped - 18 lines] > 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. Methinks it will make them think once that you're going to be far too much grief to be worth the money. > > > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All > > > other emissions readings were within tolerance. The MOT tester [quoted text clipped - 21 lines] > 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 -- > > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other > > emissions readings were within tolerance. The MOT tester seemed to think [quoted text clipped - 16 lines] > 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 only it was that easy !!! i take it you've not had much dealings with the more modern motor vehicle ? Reg > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other > emissions readings were within tolerance. The MOT tester seemed to think [quoted text clipped - 8 lines] > with a computer or £45 + VAT if a manual inspection is necessary. I make > that about £42 and about £53 in real money. Is this a reasonable price? If you gave us the actual figures we might be able to help. Tim. > > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. > > All other emissions readings were within tolerance. The MOT tester > > seemed to think this was the CAT, but that was only replaced in > > November 2005. What are the other likely culprits for a higher than > > legal CO reading?.... > If you gave us the actual figures we might be able to help. 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.  SignatureLin Chung. [Paste ntlworld over the Water Margin to send a private message.] > > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other > > emissions readings were within tolerance. The MOT tester seemed to think [quoted text clipped - 12 lines] > > Tim. 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. >> > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other >> > emissions readings were within tolerance. The MOT tester seemed to [quoted text clipped - 48 lines] > 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. > >> > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All other > >> > emissions readings were within tolerance. The MOT tester seemed to [quoted text clipped - 51 lines] > Sure it was warmed up properly? Otherwise from those readings you are > looknig at a new cat. Yes, I'm certain it was warmed up properly. I took it for a motorway run on the way to the test. >> > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All >> > other emissions readings were within tolerance. The MOT tester [quoted text clipped - 45 lines] > No change in driving behaviour of the car. No warning lights > illuminated. Yes I have a Haynes manual. 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 > As we've seen recently, I'm no expert, but...... SO SHUT THE f.ck UP THEN BEFORE YOU MAKE AN a.s OF YOURSELF. > Your HC level looks high to me, despite it passing. Every emissions > report I've seen has shown less than 10 on HC. Too late.... > AFAIK, Hydrocarbons = unburnt fuel, which should not be in the exhaust > even at the pre-CAT stage. Utter rubbish. The only way you'll get them not there is to turn the engine off. > Furthermore, I would expect the unburnt fuel > to result in a bad (rich) lambda reading. Wrong again. Lambda sensors measure unburned oxygen. SignatureConor "You're not married,you haven't got a girlfriend and you've never seen Star Trek? Good Lord!" - Patrick Stewart Conor <conor.turton@gmail.com> wrote in news:MPG.1ffe1181baab04a6989886 @news.karoo.co.uk: > SO SHUT THE f.ck UP THEN BEFORE YOU MAKE AN a.s OF YOURSELF. 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. >> AFAIK, Hydrocarbons = unburnt fuel, which should not be in the exhaust >> even at the pre-CAT stage. > > Utter rubbish. The only way you'll get them not there is to turn the > engine off. 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? >> Furthermore, I would expect the unburnt fuel >> to result in a bad (rich) lambda reading. > > Wrong again. Lambda sensors measure unburned oxygen. That's more like it. A snippet of helpful information amongst the barrage of narrow-minded insults. Keep smiling, Conor :-) Stu > Conor <conor.turton@gmail.com> wrote in news:MPG.1ffe1181baab04a6989886 > @news.karoo.co.uk: [quoted text clipped - 4 lines] > born without the benefit of infinite knowledge and have to go through > what we refer to as 'education'. So did I. I guess mine was better than yours. > 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. www.justfuckinggoogleit.com SignatureConor "You're not married,you haven't got a girlfriend and you've never seen Star Trek? Good Lord!" - Patrick Stewart >> Conor <conor.turton@gmail.com> wrote in news:MPG.1ffe1181baab04a6989886 >> @news.karoo.co.uk: [quoted text clipped - 6 lines] > > So did I. I guess mine was better than yours. I'm glad for you. Say what you wish, as I refuse to be trolled into a flame war. Stu >> Furthermore, I would expect the unburnt fuel >> to result in a bad (rich) lambda reading. > > Wrong again. Lambda sensors measure unburned oxygen. Yes, too much O2 gives a lean reading, too little O2 gives a rich reading. How was he wrong? SignatureDavid Taylor > >> Furthermore, I would expect the unburnt fuel > >> to result in a bad (rich) lambda reading. [quoted text clipped - 4 lines] > > How was he wrong? He seemed to think the Lambda Sensor picked up HCs which it doesn't. SignatureConor "You're not married,you haven't got a girlfriend and you've never seen Star Trek? Good Lord!" - Patrick Stewart >> >> Furthermore, I would expect the unburnt fuel >> >> to result in a bad (rich) lambda reading. [quoted text clipped - 7 lines] >> > He seemed to think the Lambda Sensor picked up HCs which it doesn't. Directly, no. That wasn't what I meant at all. Sorry if it came across that way. Stu >>> Furthermore, I would expect the unburnt fuel >>> to result in a bad (rich) lambda reading. [quoted text clipped - 5 lines] > > How was he wrong? 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 >>>> Furthermore, I would expect the unburnt fuel >>>> to result in a bad (rich) lambda reading. [quoted text clipped - 16 lines] > >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. >>>>> Furthermore, I would expect the unburnt fuel >>>>> to result in a bad (rich) lambda reading. [quoted text clipped - 29 lines] > HC 117ppm (assuming hot engine) then it points to the cat not doing > its job. Right. The flaw in my thinking was I didn't realise that the CAT burns up the HC, aswell as converting the CO and nitrogen. So I thought that 10ppm from the tailpipe equaled 10ppm at the manifold. All understood now, thanks :-) Stu > >>>> Furthermore, I would expect the unburnt fuel > >>>> to result in a bad (rich) lambda reading. [quoted text clipped - 29 lines] > HC 117ppm (assuming hot engine) then it points to the cat not doing > its job. Thanks for all the replies so far. I have decided that given the general state of the car (rusty wheel arches, rusty bonnet, broken door lock, tired interior) and the possibility of a £150ish bill for a new CAT and whatever new rear brake shoes cost and the possibility of new rear brake drums and cylinders being added into the bill, not to mention a CV joint which is beginning to knock and will need attention in the near future, that it is time to search the papers for a slightly less scruffy car with some MOT and tax still on it. If anybody in the Southport area wants any parts off a "Teal" metallic green Citroen AX then feel free to email me at achecsg at hotmail dot com and make an offer. David. >>>> Furthermore, I would expect the unburnt fuel >>>> to result in a bad (rich) lambda reading. [quoted text clipped - 17 lines] > > Stu It's not unknown, but if the lamda sensors dead then the lamda will be wrong, which it wasn't. You always get some HC pre the catalyst. > >> > My 1996 Citroen AX 954CC has failed its MOT on CO emissions. All > >> > other emissions readings were within tolerance. The MOT tester [quoted text clipped - 63 lines] > > Stu here you go, all about Lambda sensors http://www.picotech.com/auto/lambda_sensor.html |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.