`02 C270 CDI Auto emissions fail on MOT

[Dannyboy201062]

Hi All, I recently bought a minter C270 CDI, approx 120,000 miles. It surprisingly failed the emissions test on the NCT ( Irish MOT ) . "Smoke" reading was 3.750 / m.....the limit is 3.00/m @ 81 deg. oil temp. . This is the only item tested on emissions in the NCT. It drives very smoothly and seems to have been serviced well and recently. The only anomalies, are you do get smoke when you accelerate hard ( See it in the lights in the mirror at night ) , I considered it normal for a diesel. , it does idle a little erratically, it does seem to run cool , ie..takes forever to get up to 80 Deg ( or whatever half way up the gauge is ) .....runs at about 40 deg for quite a while. Fuel consumption is fine ....39 mpg tipping around ( 6 miles journeys rural ) and 46mpg on a longer run ( motorway 50 miles ) I had actually dosed the full tank twice , prior to the NCT, with a known good additive for improving emissions ( Dipthane ) . I`ve had a few diesels ( VW, Citroen, Peugeot ) but none have failed emissions.

Reading the forum, not much info on diesels failing emissions.....my plan is as follows:
1) Change the engine oil ,air and oil filter and stat. .( Going to do it anyway )
2) Read the fault codes ( No eng management light issues ) change the
lambda sensor if any codes for that.
3) Clean the MAF using a good carb cleaner. ( Spraying while removed )
3) Give it a good thrashing ( within rev limit ) by holding second gear while
dosing with more diaphtane. Hopefully the smoke in the mirror will
have reduced ........return for retest.

Any advice welcome......I haven`t dealt with this problem before. Presumably if the injectors were an issue it would not run as sweet as it does ( except for idle ) and fuel consumption would be poor. It does put a puff of smoke out on cold start ( starts instantly ) but I considered that normal for a diesel. There is an occasional electronic clicking sound sometimes on start up and for a short while afterwards which I put down to a glow plug system glitch.
Any Diesel merc experts out there ?
Thanks in advance........Dannyboy.

 

[turbopete]

change air filter and thermostat for DEFINITE. id also change the fuel filter for the emissions, and run some diesel injector cleaner through it.

there are no lambda sensors on a diesel so you can really forget about that, and cleaning the maf may help a little but its unlikely.

if it were my car, id change air filter, fuel filter, change thermostat, fuel system cleaner added (half to filter and half to the tank, idealy with relatively little fuel in the tank) then id warm it up and give it a good thrashing (hard accelleration as well as high revs) to the MOT centre and get them to do the emissions FIRST while its still hot!

 

[Ricardo_e220]

I agree with Pete here it needs an 'Italian tuneup' if it's being driven gently then when they rev it up will dislodge years potentially of rubbish. I've been running mine recently on more millers type stuff and it's much cleaner on kickdown.

 

[Alex Crow]

There are a number of things that could cause the issue (like worn spindles for the inlet port flaps), but the easiest way around it is the good thrashing approach - the cats will store a certain amount of particulate material, which will be ejected under high engine loads. It makes sense to clear this out with a hard rive with lots of 100% load several times, until the smoke is vastly reduced.

Failing that, unplug the airmass meter, it will probably go limp and easily pass...

 

[panason1c]

The lumpy idle might be an injector fault (dribbling?), and causing the high smoke reading.

I would perform a leak-off test.......dead easy......just unclip all the fuel return pipes off the top of each injector and run the engine at idle and then see if all injectors dribble equally from the top. It is normally only a small dribble and doesnt make a mess.

 

[Dannyboy201062]

Thanks Guys for the response.....will let you know how I get on .
Dannyboy

 

[Dannyboy201062]

Passed the emissions retest

Did most of the above, Fuel, air , oil filters and oil change and the thermostat. Strong dose of emissions reducer ( Diaphtane ) Some italian tune ups . Boot to the floor from standstill several times when warmed up, car accelerated well, changes gear at 4,000 rpm approx. Smoke seemed to be much reduced on kickdown.

Took the advice ( not so sure now ) of a local guy I know, good mechanic, maintains a fleet of Merc diesel taxis......put 5 euros ( 3/4 gallon ) of petrol into a 1/4 tank of diesel.......give it plenty of boot when warm and you will pass easily. I sent SWMBO off the next day to get the retest, got several calls...car wouldn`t start Twice.......started with difficulty. Told her to put 10 euro of diesel into the tank on top of the mix. She did.........passed the test ....emissions was 2.00 whatever as opposed to 3.7 ???. the limit is 3.0.

Don`t think I will try the petrol in diesel trick again.....car didn`t like it . Filled up with diesel after the test and it was back to it`s sweet self ....heats uo to approx 90 deg on the gauge and the the irregular idle is gone.
I`ve since heard of an additive to reduce emissions...." Eco diesel " Anyone heard of it ? ......its an additive you put into the tank. We don`t have eco diesel fuel avail here at the pumps in Ireland.
Tks for the advice.........Dannyboy.