R129 SL500 MOT failure

[Hoolio]

Hoping someone can help, please. My 96 SL500 failed its MOT today on emissions. What should I be looking at to rectify please? I should also point out that the garage had to add fuel cleaner to get the emissions down to this, was much higher before.

Engine Oil Temp - Actual 94
Fast Idle Test 1
CO - Actual 0.7%
HC - Actual 60ppm
Lambda - Actual 1.02

Fast Idle Test 2
CO - Actual 0.6%
HC - Actual 67ppm
Lambda - 1.01

Natural Idle Test
CO - Actual 0.3%

Thanks in advance.

 

[David44]

How old is the fuel the tank? Could it be just bad fuel...guessing the car has had very little use over the past few years.

 

[Hoolio]

How old is the fuel the tank? Could it be just bad fuel...guessing the car has had very little use over the past few years.

I don't have any paperwork with the car to suggest the fuel tank has ever been changed.

The fuel IN the tank is fresh and I've been using the car for the past few weeks.

 

[Wearsthefoxhat]

I think that they need to be thoroughly warmed up first..

 

[Hoolio]

I think that they need to be thoroughly warmed up first..

I drove it there like an Italian.

Last year, same MOT place, it was high on CO they added fuel cleaner and it passed.

Can't remember if it has E5 or E10 in it currently, that's the only difference I can think of.

 

[zipdip]

Well the garage has pointed the way by adding engine cleaner,the best way forward is to get your fuel tank to about a quarter full,find a quiet industrial site on the day of the re test and pour the whole bottle of say RedX in and then rev the car in low gear and warch the smoke come out when it clears run the car to the test centre and keep the car running until they want to examine it.

 

[Flyinspanner]

Cataclean is a good additive to help. Full bottle in a partial tank, and drive it hard - low gear hold to get revs up.

IIRC should the lambda be below 1?
Maybe very carefully clean the MAF sensor with isopropyl alcohol? (Or replace it).
MAF faults usually do not throw up a fault code - so can ‘appear’ ok when they are actually failing.

In future use cataclean in the 2/300miles leading up to the mot.

 

[grober]

LAMBDA SENSOR- THE UNIT HEATER OR ITS SUPPLY CAN GO BAD.

MAF AS SUGGESTED--CHEAP CLONES CAN FREQUENTLY GO BAD-USE ONLY MB OR OEM QUALITY.

THROTTLE BODY INTERNAL WIRING CAN GO BAD AFECTING IDLE BUT USUALLY DRIVEABILITY IS AFFECTED TOO

 

[jasmine]

MAF was faulty on my 500 when i bought it . running very rich and stank of fuel '
tried the cleaning method but wasnt expecting much joy as used on other cars with little success. and as expected it did nothing.
at the time merc were quoting well over £300 for a new maf ( m119 )
found a new genuine Bosch one on line for under £200 with a 5 year warranty. ( took some finding though ! )
fault cured

 

[Hoolio]

I think that they need to be thoroughly warmed up first..

I drove it there like an Italian.

Last year, same MOT place, it was high on CO they added fuel cleaner and it passed.

Can't remember if it has E5 or E10 in it currently, that's the only difference I can think of.

Cataclean is a good additive to help. Full bottle in a partial tank, and drive it hard - low gear hold to get revs up.

IIRC should the lambda be below 1?
Maybe very carefully clean the MAF sensor with isopropyl alcohol? (Or replace it).
MAF faults usually do not throw up a fault code - so can ‘appear’ ok when they are actually failing.

In future use cataclean in the 2/300miles leading up to the mot.

Lambda should be 0.97-1.03 so just passes on that. Will get some Cataclean as you suggest.