Results were:

High Speed Emission Results (25 mph):

HC Standard 120 Test Result 119 PASS (barely)
CO Standard 0.67 Test Result 0.06 PASS
CO2 Test Result 14.9
O2 Test Result 0.1
NOx Standard 848 Test Result 248 PASS
DILUTION Standard >6 Test Result 15.0 PASS

Low Speed Emission Results (15 mph):

HC Standard 124 Test Result 463 FAIL
CO Standard 0.69 Test Result 0.27 PASS
CO2 Test Result 14.7
O2 Test Result 0.4
NOx Standard 848 Test Result 1345 FAIL
DILUTION Standard >6 Test Result 15.0 PASS

Took the car to an independent, just across the state inspection. Result: "Checked EGR, OK. Oxygen sensor, OK. Recommend new Catalytic".

Took it to the MB dealer:
Results: "Catalytic OK, injectors OK. Recommend innitially to replace air injection check valve and MOT valve, remove intake manifold and replace EGR tube. Price: $900.00. However, final price can only be determined after performing first phase".

The car has 127,000 miles and had the 120,000 revision made at the MB dealer. Has new oxigen sensor, air flow meter, plugs, etc... No codes (single blink) and the only abnormality is a slightly fluctuation in idle speed (between 500 - 700 rpm).

Need someone to give me a clue of the probable causes and a sequence of tests I could perform to find them and get them fixed.

Just buy a can of "Guaranteed to Pass", follow the directions and should you be fine. Then spend your money on somethink when it actually breaks.

How far did you drive the car before doing the test? It should be driven at least 15-20 miles before you get anywhere near the DEQ. This make sure that everything is warmed up and operating at peak efficiency.

Last year I took my wife's 1995 E320 wagon with 50,000 miles on it to the DEQ nearest our house, about 3 miles away. It failed miserably.

Next day I drove it the 15 miles to the DEQ testing station very near my office. It passed with flying colors. This was totally due to the car being warmed up and all of the emissions equipment working well. Take it for a long highway drive before going to the testing shop.

Cheers,
Gerry

This sounds like a typical case of the converter being too cold.

I assume you live in California?

Go to a drivethrough place with a short line after driving the car at least 15-20 minutes including a freeway hop, and drive it aggressively.

Keep the engine at 2000 revs in neutral with the AC on and the window/sunroof open to keep a load on the engine until the tech is ready to drive it onto the rollers.

Note that your 15 MPH O2 is 0.4% percent and only 0.1% at 25 MPH. This is the tipoff that the converter was too cold, and it could not use all the available oxygen to oxidize HC and CO. Likewise, a cold converter will not reduce NOx efficiently.

What were the conditions of your test? Did you just drop off the car and come back later? Did you wait, but shut off the engine?

I don't think there's anything wrong with your car. Mercs need proper "pre-conditioning" or a cold converter will bust the first test with the second test being okay because the converter heated up to proper temperature during the first loaded test. Owners need to be aware of this and properly "manage" their emissions test.

I've measured the converter inlet nipple temp on my car with an IR gun after a normal drive, and then after five minutes of idling. The measured surface temp dropped from about 600 to 300 F.

BTW is your engine a M104 twin-cam or the M103 single cam, and is it a KE fuel system or the later all electronic system with solenoid injectors. Sorry, but I can't keep all the various model/engine configurations straight.

Duke

Thanks Deanyel,

Indeed I already bought the "Guaranteed to Pass". But I would like to hear from the Forum before having the car reinspected. It is amazing how expensive an MB problem can be if you just go directly to a repair shop (sometimes without actually solving your problem). On the other hand, information you collect through the Forum usually brings you the solution and at a fair cost.

Duke2.6 and Gerryvz gave similar replies to the thread, so I am answering both here:

I live in Houston, TX. I drove some 10 highway miles to get to the inspection site and the car got there fully warmed-up. However, I had to wait (car parked, engine off) for some 45 minutes. The inspector took the car for a 5 minute ride around the block before running the emissions test. Probably this was not enough to bring it to temperature.

What I intend to do next is to use the "guaranteed to pass" and discuss the issue with the inspector up-front (will bring print-outs of these threads), to be sure the car is tested at correct engine/catalyst temperature.

Hope it works!

>>No codes (single blink) and the only abnormality is a slightly fluctuation in idle speed (between 500 - 700 rpm).

Need someone to give me a clue of the probable causes and a sequence of tests I could perform to find them and get them fixed.
>>
No codes stored on led/sw is just Check Engine module.
Are you getting a single flash [ no codes stored ] on pin #8 ???
You want to see what is stored on the HFM-SFI module. [ pin 8 with a homemade led tool]
That will give you fuel/ignition malfunction faults.......is any

In CA we have drive through inspection stations - similar to a car wash. One not far from me has three lanes and is "test only" (They do not do repairs.), which I have to go to since CA has deemed most Mercs of my vintage as "high emitter profile" and we have to be tested at "test only" stations.

Letting the car sit for 45 minutes - even with 5 minutes of driving is not enough to heat up the converter, and it shows in your numbers.

Find a place where you don't have to wait long and keep the engine revs up as I previously suggested. If possible, drive the car around the block (hard) a couple of times just before you go on the rollers.

These cars are very sensitive to "conditioning" because the converter is relatively far downstream from the exhaust manifolds. Modern cars are going to "maniverters" where the catalyst is literally bolted to the exhaust manifold outlet or as close as possible.

I'm still curious as to your engine and fuel system type. The KE systems seem to be inherently "dirty", and I think it is due to fuel flow variation at low flow rates such as is the case at idle. Pulse type solenoids injectors seem to be better at delivering consistent fuel flow to each cylinder at idle.

In CA some stations will do a "pretest" for a fee. Basically a ripoff IMO, but the pretest will usually get the catalyst up to temp. Also, there is a "tire dry procedure" that can be used in wet weather. The tech runs the car at about 25 MPH with no load for 30-60 seconds, then starts the test. I had this done once and the 15 MPH HC dropped about 20 percent relative to the previous test. On my last test I went on a dry day and the 15 MPH HC was back up - squeaked by with 1 PPM to spare.

Duke

Arthur,

Thank you and sorry for my late reply. Indeed I was building a LED Tool to properly check the codes.

My E320 is an early 94 (manufactured 07/93) with M104 engine. I checked all active pins, with results as follows:

Pin 4 (CEM) - 1 flash
Pin 7 - 1 flash
Pin 8 - 1 flash
Pin 10 - No flash
Pin 14 - 11
Pin 16 - burned fuse after fuse (3 total), couldn't read

I built the LED tool as described in Jim Forgione's site, except that I couldn't find the 0.1 amp fuse and used 0.25 amp instead (lowest I found).

I don't have a "code table" so I am not able to interpret the results above. Could you translate them?

I am concerned with no flash in Pin 10 and the fuses burning while trying to read through pin 16.

I also noticed that, while the ignition switch was on and the hood open, there was a constant noise coming from the throttle valve. I never heard that before, although I never had the hood open with the ignition on. Is that noise normal ?

This is my first MB. I bought it used 3 1/2 years ago from the original owner. It had 73K miles at the time and was in great condition. I have been doing myself all the maintenance (except the 120K revision - took it to the dealer to double check - considered excellent at the time). However, this is the first time I face something not "purely mechanical" and I need to learn about it.

I noticed you have been giving great advice in the Forum and I am glad you answered my thread.

I would be willing to bet, the fluctuation in idle speed ( 500 - 700 rpm ) is the culprit of your failure.
At 15 mph, you're barely above idle.
Next clue would be " the constant noise from the throttle valve ".
Is it trying to compensate for something ?
Hell, Im tired & going to bed.

__________________
2007 C 230 Sport.

Code 11 is Closed throttle recognition fault or Electronic accellerator [EA]problem.
First thing is to see if the cable has a little slack It should and there is an adjustment . Also check that the pedal is working free [ nut bunched up rug, etc]

The reason for blown fuse on pin 16 is that pin 16 is actually Pos12v , not a diagnostic plug.
Pin 10 is mute
The tool you made is universal , whereas the one for your car specific would use pin 1 for ground, pin 16 for B+, and the other lead will be the probe/test lead that goes to the designated sockets.
You can modify your by simply putting banna plugs on the pos and neg ends of the tool and use pin 1 and 16 for power...then you do not use the battery for power, rather , all 3 bannas go to the diagnostic socket.

I will check the cable and adjust it. Pin 16 being +12V explains the blown fuses. How about the noise coming from the throttle valve ?