Another failed emissions test - PeachParts Mercedes-Benz Forum

lilblkbnz · #1 06-14-2007, 07:41 PM

I did a search before posting but i didn't find a clear answer. My 87 420 failed the New Jersey emissions test today. Here's my numbers:

Gas Standard My Reading Result

NOx ------- 990 ----------248 ------------Pass
HC ---------134 ----------294 ------------Fail
CO% -------0.75 ---------4.77 -----------Fail
CO2% ------8.9
O2% -------1.9

Could these numbers have anything to do with mixture settings/duty cycle? The PO of this car messed with the mixture trying to fix a high idle problem. I've set it using instructions from the landiss.com website. I have not been able to get it to 50% duty cycle, closer to 60% is the best I could do. The oxygen sensor is new, plugs have about 2k miles and the car just had an oil change. Air filter is also new. The car seems to run good, no misses. The only noticeable problem is a surge on decelaration which I posted about earlier. Any ideas?? Thanks for any help.

raymr · #2 06-14-2007, 07:50 PM

Are you seeing the numbers jump around some? Mine seems happiest around 70% (is an '85 which I understand is different from subsequent years) but it fluctuates between 67 and 74.

mbdoc · #3 06-15-2007, 08:13 AM

The engine is running WAY too RICH! And the O2 sensor isn't controlling the mixture..adjust first & if needed replace the O2 sensor.

Trojadc · #4 06-15-2007, 08:47 AM

Mr Dalton, you want to handle this one... You are my emissions guru!

david s poole · #5 06-15-2007, 09:39 AM

as M.B.DOC says you are running way too rich.what kind of emmissions test is run in your state?for the o2 sensor to control your mixture needs to be around 14.4 air to fuel and by the numbers yours is closer to 12.0.first lean down with 3mm ccw at the tower in front of fuel distrib until idle rough then cw a little.now you may discover why po richened the mixture.probably to cover up one or two vacuum leaks[maybe more]

Texholdem · #6 06-15-2007, 10:21 AM

Hi David,

my engine was running too lean, right? And you tuned it fine

. Glad to have it done.

Take care!

david s poole · #7 06-15-2007, 10:39 AM

yes your engine was too lean to the point that all available richening was used up at idle.

manny · #8 06-15-2007, 11:19 AM

4.77 % CO ?
Don't let anybody stand behind your car,.....they'll drop like flies.

lilblkbnz · #9 06-15-2007, 08:53 PM

Thanks for the responses. It was a little stinky out back

Today, after reading the responses here I went back with my meter and tried resetting the mixture. With the car at operating temp, I turned it CCW until it started to run rough and then back CW until it smoothed out again. It only took maybe 1/4 turn to get it back smooth. It's not stinky any more but the meter is still bouncing between about 54% and 65% at idle. At 2500 rpm it shows about 74%. Seems like the numbers don't change no matter what I do with the adjustment screw. This oxygen sensor is only about 2500 miles old. Maybe I got a bad one? It's a Bosche unit but I don't remember the part #. I've checked for vacuum leaks and did find a couple, those have been fixed. I used carb cleaner to find them and I'm not finding any new ones. Since it doesn't stink anymore, should I go back for another test now?? The test is free and I have up to 45 days to re-test. By the way, the test is called ASM 5015 Enhanced Emissions Test and Safety. Sorry for being so uninformed on this subject but I've never lived in a state where a car this old had to pass emissions testing. What a PITA! Thanks for the help guys, any other suggestions more than welcome. I'll post results of my re-test.

manny · #10 06-15-2007, 09:39 PM

If the test is free, hurry back there.

lilblkbnz · #11 06-22-2007, 02:12 PM

OK guys, I finally had the time to go for a re-test today. Failed again!! Here's the new #s:

GAS: STANDARD MY READING RESULT

NOx 990 2777

Fail
HC 134 45

Pass
CO% 0.75 0.00

Pass
CO2% 12.6
O2% 2.2

The only thing I've done since the first test was turn the 3mm adjustment screw CCW to lean the mixture. My previous readings were NOx 248 -- HC 294 -- and CO% 4.77%. Nothing else has been touched. Does this mean I'm too lean now??

manny · #12 06-22-2007, 03:52 PM

Looks like you went too lean.
Your CO = 0.00 %, and your O2 is high.
This would elevate NOx.
Go the other way ( rich ) about 1/2 of what you did before & try again.
It's a game of patience ( without an exhaustgas analyzer ).

david s poole · #13 06-22-2007, 04:52 PM

hope you made a note of how far you went.you need to cut it in half and go back.i bet the emmissions place has a manual setup on their analyser.why not ask if can use it and adjust mixture while running.then you can get it right.

lilblkbnz · #14 06-23-2007, 12:09 PM

Thanks guys, I'll try to richen it up just a tad. I'll ask the guys at the inspection place if I can adjust it while running. I never even thought of that. I would be surprised if they let me do it though, these guys act like they are some kind of god or something. The most unfriendly bunch I've ever seen. They make you feel like a criminal. They won't even let you stand near your car while testing. But the tests are free so I guess I can't complain too much. The test is done on a dyno and I think they do it under load at 25mph. I'll ask and see what they say. I'm planning to re-test early next week and I'll post results when I do. Thanks very much for the inputs.