w124 mot fail emissions

[mattc]

Hi all

Nats 1993 e280 has just failed MOT on the following.

exhaust emissions carbon monoxide content after 2nd fast idle excessive.
exhuast emissions Lambda reading after 2nd fast idle outside specified limits

oh, and he did not like the front indicator bulbs (thought they were a bit dim) - so new bulbs for them.

here's the test data

fast idle test

CO max 0.2 actual 1.492
HC max 200 actual 151
Lambda min 0.97 max 1.03 actual 0.967

second idle test

CO 0.2 actual 0.534
HC max 200 actual 91
Lambda min 0.970 max 1.03 actual 0.995

Natural idle tst

CO max 0.300 actual 0.290



The car has only be on local journeys round Brum for a few months now - no motorway speeds at all. Like an idiot I did not take it for a long high speed run beforehand which I have heard can "blow out" the gases. But is there something specifically I should be looking to change? As far as I can tell the Cat and Lambda sensor are original (nothing in the extensive service file to indicate it has been changed either).

I think the exhaust MIGHT be leaking so can this be part of the problem?

Thoughts please before I simply start swapping parts.

I should also add as I am moving home by the end of next week the estate is being rpressed into ferrying duties so not really able to leave it with a garage whilst they diagnose the cause.

matt

 

[SilverSaloon]

take it for an "italian tune up" (thrash and redline it) after adding some of that injector cleaner stuff into the fuel tank.

Make sure the car is fully warm before the MOT takes place

Make sure the exchaust is not blowing anywhere.

Other than that, i cant help

 

[MBK]

I agree with the above, i take mine for a good long drive on the m40 and the down M4 back to west london before mine goes for its MOT passes every time

 

[bouncer]

Mattc,

Check list.

Air leaks before or after or at the oxygen sensor! ( the just out of bottom tolerance lambda reading 0.967)
Misfires?
Faulty coolant temp sensor!

If not, then looking at the readings the oxygen sensor has become "Lazy" This can be seen as the second fast idle test is done the readings are starting to come into line.
Note the recovery of the Lambda reading to near enough lambda 1
Note the drop in HC (unburnt fuel) this shows the cat is still working, and also the drop in CO, its dropped by two thirds on the second fast idle test.
In my opinion new Lambda sensor will sort this out.
Not being driven a lot will do this to lambda/oxygen sensors.

Hope this helps


sTeVe

 

[mattc]

cheers for the replies guys.

I will change the lambda sensor and take it for a bloody good blast (though not tomorrow as it looks like weather will be ghastly.)

Should I get a MB sensor or an aftermarket one? Is the aftermarket one a false economy?

I will report back in a few days

 

[BlackC55]

Get a Bosch sensor. ECP do them.

 

[mattc]

just looking at ECP site and they seem to have Walker and React parts only for 280's

 

[kth286]

Get the original Mercedes one, and also get spark plugs from Merc - only about £12 per set.

But watch the bending of the wiring loom when changing plugs.

 

[Redline]

Dunno if you have petrol stations with E85 over there, but if you do, running about 50/50 with regular unleaded works pretty good as well. So if you fill it up with E85 and injector cleaner and then go for a good warm up drive I think it'll go straight through!