spetz

Hi guys,
My C124 failed an emissions test.

Now, what could it be?
The values for CO were 1.1% (.5% limit) at idle and 1.4% (.3% limit) on an accelerated test.

Lambda came in fine.
Does this mean the O2 sensor is ok?

The car has 63K miles and is extremely well maintained. It gets driven very rarely, could this cause this problem? Less than 1,000 miles annually.

Also, I assume doing an "injector clean" should make it pass, but is this a band aid solution, or could it just be clogged fuel system, poor spraying injectors etc?

E420guy

I always do an oil change and a spark plug change before I have to do an emissions test as well I fill my tank with premium gas and runs some octane boost before I go in. My friend took his 1999 S500 for an emissions test and he failed, but after doing nothing more than what I just mentioned he passed. Try it...I've never failed and I this is what I do...New plugs, an oil change, and fill up the tank with Premium and a bottle of octane boost.

spetz

The oil is new, the plugs just about 5,000km old (but maybe 3ish years) and it always get premium fuel.
It was a surprise that it failed as it truly is in pristine condition and drives like new.

Could it be that due to it sitting for extended periods this would cause it? It is not unlikely for it to sit for over a month without being started/driven.

What I plan on doing is a new fuel filter and then some fuel system clean/throttle body clean. If this still fails I will look into the O2 sensor and/or cat

RobertG

High co means it's running rich(air filter dirty, leaky injectors or poor spray pattern).

spetz

Thanks Robert,
Could it be the oxygen sensor?
Or cat?

RobertG

Do you have any codes?

spetz

The CEL light is not on, but did not do a diagnostics test.
Do you recommend one?
The car runs perfect though, I am genuinely surprised it did not pass

larryj

Injectors. They tend to clog up with dried fuel residue if left too long without a good drive. Add a bottle of Techron to about 1/2 a tank of gas (2 bottles to a full tank) and then take it for a nice weekend drive, say at least 2 - 3 hours. When the injectors "clog", I do not mean that they are stopped up, they are just not forming the correct spray pattern (no necessary "mist" but a "stream" that does not properly vaporize, causing incomplete combustion). Sometimes these vehicles NEED a good hard run......they were meant to be driven....hard...just like a fine thorobred horse!

Floobydust

To me, increasing CO with engine speed (e.g., run versus idle) suggests a dirty air filter, dirty or malfunctioning MAF sensor, a low coolant temperature (or faulty temper sensor that makes the ECU think the coolant temperature is too low), or a bad catalytic converter. I would think that with dirty/leaking injectors the CO values would improve with engine speed due to increased cylinder turbulence. If the air filter is not new, I would suggest replacing that first.

I do think there is something to the "additives" helping with this type of problem in that they displace gasoline as part of the fuel and thus decrease the oxygen required for complete combustion, thus decreasing the CO.

spetz

I just bought some BG44K to clean out the fuel system. Before adding it though I will replace the fuel filter.
Should I do the emissions test while there is some BG44K in the tank or should I fill up again before doing the test?

Floobydust I hope you are wrong

Ricks170.465

If my 2001 slk320 did not pass an emissions test the first thing I would do is install my OBDII reader and look for a code, it could have a pending code and not trip a check engine light. I am not quite sure if the age of your car might be the OBDI diagnostic version, but it should show on an emissions placard in your engine compartment. Also I agree that the car should be run at least 20-30 min before you go to the testing station, they have even asked me that question in the past before I did an emissions test. If you do not have a code reader I think Autozone or one of the other parts stores can do a code check for you free. it will give someplace to start at with a generic code.

spetz

Going through my maintenance log/receipts, I have done the spark plugs and air filter about 2,500 miles ago, but this is about 3-4 years ago.
Could they degrade with time and cause emissions issues?

Floobydust

Fouled/dirty spark plugs = misfire = high HC

Dirty/clogged air filter = air restriction = not enough O2 = high CO

I don't know what your location is, but with the climate here in New England, storing a car can cause deterioration of paper filters because the air often becomes super saturated with temperature changes. This is particular true if the car is stored in a poorly ventilated (summer) or non-heated (winter) garage. I had the HVAC particulate filters clog up because of this effect.

If you have access to someone with a CO/HC meter, try checking the car out with the air filter removed (obviously, don't leave it that way for long).

RobertG

How old is the fuel in the tank?
Today's fuel with 10% ethanol has very short shelf life without any additives.

spetz

I cannot remember the last time I put gas in it, maybe 2-3 months, though I do not put gas with ethanol in it

RobertG

I would run the car till you use up all the old fuel and the put fresh stuff in and try the inspection again.

spetz

Well the plan is to use up the fuel, put more fuel in + fuel system cleaner and then after 2-300 miles take it for the inspection again
I am worried about it being a number of things (cat, MAF, O2 sensor)

Floobydust

A 1994 E220 tells me you are probably in the UK or Europe. As far as I know, mandatory "oxygenated" fuels (EtOH, MTBE, etc.) are a North American thing, primarily for lower emissions. Nevertheless, old gas can be problematic because the volatile fractions can polymerize or evaporate, thus decreasing the volatility of the fuel which makes it harder for the injectors to vaporize for ignition.

If you're brave, try the MOT without the air filter unless it's a physical inspection item.

Ricks170.465

It sounds like you do not drive the car enough, old gas and lack of use can create problems. My SLK320 is a spare/toy and I make sure to drive it for 20 minutes 4 times a month minimum. Some recommend once a month, a good drive at operating tempature a minimum 20-30 minutes. Remember cars are machines and to maintain optimum performance a machine must be used so it will not degrade.

spetz

Anyway the problem was found...
Turns out that the car is a model without O2 sensor or catalytic converter and it was tested as one with these items.

I was surprised to find out that it had no O2 sensor or cat, is this an issue? Does this mean the engine never really runs optimally without the O2 sensor?

Ricks170.465

If your car does not have O2 sensors (2 min. pre and post cat) it may be a model originally built for a country outside the USA, check your VIN number for the orig. spec. you should be able to research it, and if it did not come with it from the factory then it should be fine as long as state emissions testers do not get their noses out of joint.

spetz

Yes I do not live in the US and the car was bought new by my dad.
It has no O2 sensor or cat, does this affect the way it drives or is it simply just for emissions?