MOT nightmare

[clk208]

Hi folks,

Took the CLK for a last minute MOT today at a back street garage. They said it was failing on emissions slightly - Lambda. Said they would try what they could to get it through - 20 mins of having the engine rev away to apparently clear things out and still no joy.

Next thing - they said it would need to be hooked up to a diagnostic computer which they didn't have but a mate at a garage had one a couple of miles away. So we drive round and leave it with them - don't think it would have been a STAR as many different makes of car being worked on. Diagnosis this afternoon - left bank oxygen sensor, but they can't carry out work til new year now. They say that even when this is replaced there may be issues with the CAT but they won't know until after.

I had the left bank oxygen sensor replaced 18 months ago - today's garage are saying it's a cheap non-OEM which is why it had failed.

However, last time my sensor failed there was some noticeable hesitation, this time it is well and truly pulling like a train - no noticeable problems at all. Had a new Bosch MAF a couple of months ago too.

Wondering if they could have a wrong diagnosis - I don't want to waste £150 for nothing (not to mention being without MOT for next week and a bit). Are there any other common faults that could cause Lambda to be out?

 

[martin_a]

When did you last give her a service? (ooer)

Sometimes new filters etc can make a difference to emissions. Not sure about lambda per say but i know a service and a damn good run can sort a few issues out.

What fuel is it on?

m.

 

[clk208]

Hi Martin,

Thanks for the speedy reply. It's a petrol W208 320.

Was last serviced in April. It had been doing a combination of very short trips, huge amounts of time idling in jams and was with a paint shop for a week (partial respray, now looking good) over the last month.

That said they had the thing blasting away at high rpm whilst stationary for about 20 mins today so you would think this would do the trick.

Gutted as was really looking forward to using the car to visit friends and family over the next week. Most of the time I hardly ever use the damn thing!!

 

[Howard]

Give it a blast on the motorway , revving high in neutral doesn't load the engine ....

Good hard boot up the slip road , drive it hard for ten miles or so then put the probe back up the exhaust , bet it's ok.

 

[d w124]

Give it a blast on the motorway

Last time I did that,my exhaust started falling appart lol

 

[flango]

Can of Forte fuel treatment or Millers before an italian tune up on the motorway. I'll guarantee it will pass.

You need to get it on star to have a look at the lambda sensor readings and see if there really is a problem.

 

[clk208]

Thanks folks!!

I give this a whirl tomorrow and have them retest the emissions then.

Cheers,

James

 

[SilverSaloon]

yes, give it an italian tune up.

if it still fails, take it elsewhere and ask them to quickly test the emissions for a few quid. if it passes then go back to the garage and ask whats going on.

i had this problem with our picasso a few years ago at a back street place. i took it elsewhere as they were quoting £350 worth of work to fix it.... it was fine elsewhere, so i went back and explained i'd had it tested elswehere and its fine, and surprisingly it passed then.....

 

[Tiff]

If its just Lambda, and its not too far out, and is high, check your exhaust very carefully for even the smallest leak- this will cause that problem. A service etc wouldn't really change this, as it would also affect the CO and HC. Can you post up the readings?

 

[grober]

Paint shop atmosphere can sometimes contain large volumes of fine particulates if lots of mechanical sanding is being done on other vehicles. This can be washed off the surface of any cars effected but if the engine is run this is going to be sucked into the engine inlet. If the air filter has not been changed since the cars stay in the bodyshop then it might be worth fitting a new one?

 

[clk208]

Thanks Tiff.

Unfortunately the garage with the code reader machine kept the bl00dy printout with the values so I don't have it any more. Only realised when I got home.

Ever since I bought the car in 2006 all four MOTs have always been pretty much at the upper limit for Lambda.

 

[clk208]

Thanks Grober - will pick up a new air filter from Hellfrauds when I collect my fuel treatment.

Has to be worth a go and won't do any harm having a new one on anyway I guess.

 

[Vlad]

It's kind of true that cheap pattern Lambda sensors are a false economy...stick with Bosch or NGK and its worth it in the long run.

 

[clk208]

Update from my busy morning - went into Halfords, picked up new air filter and some fuel treatment. Fitted the air filter and poured in the juice in the car park.

Drove up to find a suitable empty, straight and deiced motorway sliproad, gave it full power and hit 3 figures on the speedo quicker than I imagined. A few more spirited runs up to speed on an empty stretch of motorway etc over about 25 miles in total.

Found an open independent garage (different to the one where I had MOT) and got them to check emissions. Result was surprising!

Lambda now too low - should be in range 0.97 - 1.03, was 0.91.
CO now too high - should be max 0.30%, was 3.11%
HC now too high - should be max 200ppm, was 220ppm

So has kind of reversed the original result where lambda too high and everything else fine. Looks like a new left bank oxygen sensor it is then. :'(

 

[Howard]

Sorry to hear this , it was worth a try though.

 

[Ian B Walker]

Drop in after the festive season and I will plug it in for you.

 

[clk208]

Thanks Ian that would be great- will be sure to call up in the New Year for a health check.

In the meantime I am going to have a go at giving the oxygen sensor a DIY repair and try to get my MOT done tomorrow.