Emission Test Failed 85 380SE W126 - PeachParts Mercedes-Benz Forum

djb2000 · #1 05-30-2007, 02:18 PM

My Texas 380SE failed emissions testing this week. I suspected it would, I've had the car a little over a year. It's got over 250K miles but runs and drives fairly well. Can anyone give me advice on troubleshooting emission test issues based on these numbers?

_________________High Speed____________________Low Speed
Pollutant.......Standard........Current.....Result.....Standard....Current....Result
__HC(ppm)_____137_________170_____FAIL______140______178_____FAIL
__CO%________.87__________.41_____PASS_____.79_______.59_____PASS
__CO2%___________________14.5_______________________14.5______
__O2%_____________________.8_________________________.7_______
__NOx(ppm)____956_________1564____FAIL______1046____1817_____FAIL
Dilution%_______>6_________14.9________________>6_____15.1____

Gas Cap PASS

I figure it's running rich but i don't think there is any manual adjustment. I burn mid-grade fuel, 89 octane. Your help is appreciated!

raymr · #2 05-30-2007, 03:37 PM

How old is the O2 sensor? If you don't know, I would replace it first before fiddling with the mixture setting. If you car is running right, and fully warmed up, the exhaust should have very little or no odor.

Adjusting the mixture will require some studying - search this website for that, and a mulitmeter with a duty cycle function.

djb2000 · #3 05-30-2007, 04:54 PM

Raymr,
Thank you for the reply. I will be sure to replace the o2 sensor. The exhausts doesn't smell too much.
djb2000

david s poole · #4 05-30-2007, 04:56 PM

i think that you need another fuel distributor.there is too much o2 in the exhaust and that is probably from one or two cylinders not getting the same amount of fuel as the others.if correct you should see o2 levels down to .2 or .3%.try running engine at idle in gear with emergency brake on and open the fuel lines at the distributor one at a time and see if one or two don't make much diff.

djb2000 · #5 05-30-2007, 08:02 PM

dsp,
Thank you for the reply. I know the injectors are very old, i cleaned a few with carb cleaner as an experiment. I will consult my manual to see how to adjust at the fuel distributor as you described. Thanks again!
db

OMEGAMAN · #6 05-30-2007, 08:33 PM

Does it still have a catalytic converter. Looks to me like the converter was too cool to perform on not there at all. CO is the measure of how much fuel your burning and you look just fine. .5 to .8 is just about right but definatly not too rich.
The convertor cleans up NOx and Hc. If it isnt workin proporly you will have high readings. You might try and run it really hard in the interstate and drive imediatly to the emmissions station and try again

djb2000 · #7 05-31-2007, 09:01 PM

Omegaman,
Thank you for the post. You may have something there. I've read other threads too. My mixture is probably a little rich. I think the catalytic converter is original, looks like it. Based on the NOx it probably is a combination of the c converter and fuel control.
Looks like I've got some work ahead of me on this old beater. I like driving 'das boot' because i have a long commute across downtown Dallas and don't have to worry about wrecking a new car.
I will report what happens with this project, for future reference.....
djb

raymr · #8 05-31-2007, 10:42 PM

Just a side note: my original cat just rusted out of the car last night and started dragging down the road. I have some work ahead of me too.

djb2000 · #9 12-02-2007, 08:47 PM

After 4 tries I finally got my old 85 380SE to pass state inspection. Thank you all for your posts and advice. Here's what I did...

2nd try - replaced the spark plugs, spark plug wires, and rotor cap. Changed the oil. Most readings improved but not enough to pass.

3rd try - added a bottle of high octane injector cleaner to 12 gallons of premium 93 octane gas. Cleaned the air breather and tubes to the gas recyle flow on the air pump and valve cover. Inflated the rear tires to 45 PSI (spooky step, i thought those old tires would blow up in my face). The readings improved some more and it almost passed. Still failed the low speed NOx test by 25% too high.

4th try - I figured the mixture was too lean so I adjusted the air intake to rich it up a bit and blocked the vacuum advance tube so the engine timing would not advance. I drove it 3 miles at 55mph in 3rd gear and got it tested HOT. It passed with about 5% to spare on NOx and 10% on the HC tolerance.

I guess my tired old catalytic coverter still had enough stuff to bring the NOx down to tolerable levels.