MOT Failure - Emissions
Discussion
I have just had an MOT failure, mainly on emissions.
Failed on CO (1.68%/2.47%) and HC (320ppm/223ppm) on
on both first and second fast idle tests
and on CO (2.43%) on natural idle.
Although the garage is reliable and trustworthy they admitted
that this is beyond their scope. Any help, hints or where
to start would be appreciated.
Strangely the rear fog light goes out when the headlights
are on full-beam (I obviously didn't check this properly
myself). Is this likely to be an earth problem ?
It is fine on dipped beam and side lights.
Failed on CO (1.68%/2.47%) and HC (320ppm/223ppm) on
on both first and second fast idle tests
and on CO (2.43%) on natural idle.
Although the garage is reliable and trustworthy they admitted
that this is beyond their scope. Any help, hints or where
to start would be appreciated.
Strangely the rear fog light goes out when the headlights
are on full-beam (I obviously didn't check this properly
myself). Is this likely to be an earth problem ?
It is fine on dipped beam and side lights.
Not too hot on emissions other than to say used to struggle with an old Subaru on the emissions and was always advised to take it for a damn good razzing before taking it in, nice hot engine is less likely to fail for reasons which escape me now....
Fog lights I think it might be a standard thing, you don't drive in fog with full beam as you just get bounce back, so could well be a circuit to prevent both being on together. Going back to another old car I had, you certainly could not have front fogs and full beam on at the same time so see no real reason why rears might not be the same.
My usual "talking b@llocks" disclaimer applies to my response.
S.
Fog lights I think it might be a standard thing, you don't drive in fog with full beam as you just get bounce back, so could well be a circuit to prevent both being on together. Going back to another old car I had, you certainly could not have front fogs and full beam on at the same time so see no real reason why rears might not be the same.
My usual "talking b@llocks" disclaimer applies to my response.
S.
Not too sure what the options are, mine failed on CO emissions earlier this year and at the same time seemed a bit down on power. It turned out o be a weak spark on one cylinder,a set of new plugs leads and plug shrouds solved the problem and the car was back to normal. Don't know about the HC's though. I only managed to get it diagnosed by taking it to my local idependant.
You could try pulling the breathers off the rocker covers, I had a similar problem on a land rover v8, and I put it down to blocked flame traps......think the TVR has a similar recirculation system. They can be cleaned out, but I don't think new ones cost that much. The fog light does sound like a dodgy earth, but I wouldn't think it would be an MOT failure point.......think you can get a list of MOT checks from the DOT website.
over_the_hill said:
.......
and the Lambda reading was OK.
Thats more tricky - if the lambda readings were definitely within limits, should be about 0.92 at idle, (which would correspond with a pre cat CO level of about 2.6%) then - if the cat is warmed up and working properly - the tailpipe CO level should be much lower, the same is true of the HC level. If there was some significant engine malady it's unlikely that the lambda readings would be ok, although the ECU would try to compensate via the closed loop system. High HC levels would usually imply a worn engine burning oil, or a gross fuelling error, but then the levels would be well into 4 figures (before the cat). The first place i'd be looking is the cat itself as if this isn't performing properly then both CO and HC will be higher than expected. Without wishing to be pessimistic, there is of course the possibility that the cat fails as a result of excessive oil burning causing blockage with deposits and contamination of the catalyst film. Equally poor running could be due to a blocked cat, though, as with Peters' cam suggetsion, this would be more evident at higher loads.
Try the basics before getting too up tight. Check/replace air filter, plugs. Change oil and filter and use a quality engine flush. Get hold of some Forte fuel system cleaner and put it in your fuel tank when low on petrol to give you a stronger mix. Give it a good thrash and get it nice and hot, then have the emmisions checked prior to re test... Even though we like to think we drive our cars hard in reality we dont. A lot of the emmision failures are due to carboning up and fuel/oil contamination. Steve.
Turned out to be the Lambda sensors which were on the way out
and acting erratically. So a big thanks to Mervyn at Autotune
for tracking this down and sorting it out and for dealing with
a particularly pedantic and not TVR au-fait tester on the restest.
Having been to Mervyn several times now I would thoroughly
recommend him and he also does a very good cup of tea !!
and acting erratically. So a big thanks to Mervyn at Autotune
for tracking this down and sorting it out and for dealing with
a particularly pedantic and not TVR au-fait tester on the restest.
Having been to Mervyn several times now I would thoroughly
recommend him and he also does a very good cup of tea !!
My car has also just failed on emissions, when they first tested it, it was high above 8.00, then they revved it a bit & it came down to about 3.5 so hope a blast down the motorway today will half it again! Funny though that I had a full service and an emissions upgrade just 4 weeks ago from Vauxhall (where the MOT failed) all they could suggest was to blast up the motorway & clear the soot etc from the exhaust preferably in 4th gear, I did stay in 4th gear until I hit 65 mph then stayed in 5th but if I dropped below 60 I dropped back to 4th gear again, went to Meadowhall & back (approx 60 odd mile round trip) & am not going to use the car until I take it back to re-test on Mon morning, before I went I added a well known fuel additive to the diesel & filled up as instructed on the bottle, I also added a soot reducer from the same well known brand into my oil, when my oil was warm, again, as instructed on the bottle! Here's hoping, wish me luck! Please note that my car does much better on the supermarket diesel than the "Ultimate diesel" from that well-known station, which, after a year I reverted back to the supermarket as my car runs much better & is lower on emissions! My car is a 1.5TD Vauxhall Corsa 16 yrs old but still goes like a rocket. Next year I will blast up the motorway the day before I take it in for the MOT. Here's hoping Monday is better.
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