Hi, took the zed for MOT today, all good no advisories other than the emissions on the co2 rating were high. It failed to start with and I was advised to take it for a good thrashing (staying firmly within the speed limits ). Returning after an hour the car was retested and it passed but the emissions were right on the limit. The garage suggested a lazy cat? Is this a common problem or is it just lack of use causing things to be bunged up? The cars only done 1500 miles since the last test. Thanks in advance.
Cheers
Dave
"Growing old is mandatory, growing up is optional!"
I would plug it in to diagnostics and have a look at the Lambda sensors, to see how they are performing using the live data on whatever diagnostics you are using, also have a look at the fuel trims to see what is happening. If the Lambdas are under performing it may cause it to run rich showing up on the emission test.
Make sure your air filter is clean and check out your spark plugs as well.
Colb
Colb
1999 BMW 1.8 Z3
2003 BMW 2.5 Z4
1998 Honda Deauville NT650V
Thanks colb, the lambda sensor was reading low on the MOT screen as the garage pointed this out to me. I've owned the car just a year so this is the first MOT I've had done on it. It has a full comprehensive service history and was serviced as an agreement when I bought it, I still have 3 green lights on the service indicator. I have always thought it smells hot when I've been out on a jaunt if that makes sense?
"Growing old is mandatory, growing up is optional!"
A symptom of a "dirty" or failed Cat is a high CO reading. Another cause is an overly rich fuel/air mix. However, the MOT tester can normally watch, from their sophisticated equipment, how the pre-cat lambda sensor is operating. If the pre-cat sensor is not frantically "switching" in an attempt to correct an overly rich exhaust mix then it tends to point to the cat. I would put a tin of Cataclean through the system. Does your Cat rattle when you nudge it with the palm of your hand (breaking up with age) or do you have an aftermarket Cat (quality can be variable)?
Hi Dave, what were the readings on your emissions printout ? C.O. , H.C. , and Lambda? Did the tester measure the oil temperature and if so what was it?
"Knowledge and experience are not always the same"
Del wrote:A symptom of a "dirty" or failed Cat is a high CO reading. Another cause is an overly rich fuel/air mix. However, the MOT tester can normally watch, from their sophisticated equipment, how the pre-cat lambda sensor is operating. If the pre-cat sensor is not frantically "switching" in an attempt to correct an overly rich exhaust mix then it tends to point to the cat. I would put a tin of Cataclean through the system. Does your Cat rattle when you nudge it with the palm of your hand (breaking up with age) or do you have an aftermarket Cat (quality can be variable)?
The lambda reading is the air/fuel ratio. The emissions tester does not give live readings of the lambda sensors switching an engine analyser will but not in M.O.T. mode. Cat's for Dave's year of car do not have to be type approved. A tin/bottle of cat cleaner can't hurt either.
"Knowledge and experience are not always the same"
Thanks again guys. Lambda reading was 1.0% I think? I'll stick a bottle of cataclean in then and have a service and set up done. Sounds like the running rich or cat are to blame so will go with them. A service won't do any harm anyway.
"Growing old is mandatory, growing up is optional!"
Thanks for that. I don't know what the readings should be so the mixture must be right then with what your saying. I'll get the catclean run through then get it serviced and if it's still high I'll get it plugged In to see whats going on.
Cheers
Dave
"Growing old is mandatory, growing up is optional!"
mine was high on the first test but he re-tested at the end of the MOT and it passed.....just.
1 month later my CAT disintegrated and blocked the exhaust causing all sorts of running problems.
new cat - £112 delivered from Eurocarparts - and it now runs better than ever.
). Returning after an hour the car was retested and it passed but the emissions were right on the limit. The garage suggested a lazy cat? Is this a common problem or is it just lack of use causing things to be bunged up? The cars only done 1500 miles since the last test. Thanks in advance. 
