Another failed emissions test - PeachParts Mercedes-Benz Forum

lilblkbnz · #1 06-14-2007, 08:41 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, 08:50 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, 09:13 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, 09:47 AM

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

david s poole · #5 06-15-2007, 10:39 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]