Failed SMOG high HC and NO on low speed - PeachParts Mercedes-Benz Forum

2wheelsoff · #1 05-17-2011, 10:34 PM

Need some people with emissions expertise to chime in please.

CA emissions failed:

Speed RPM %CO2 %O2 HC(ppm) CO% NO(ppm)
15mph 1608 15.2 0.3 121(fail .29 736(fail)
25mph 2236 15.4 0.1 32(at limit) 0.06 219

max HC = 57 at 15mph and 32 at 25mph
max NO = 478 at 15mph and 484 at 25mph

E320 wagon 1994 M104 with 180k (passed 2 years ago well within spec).

I had a vacuum line connected wrong off the throttle body (the one that goes to the valve that gets fumes off the charcoal canister).

I am wondering if there is anything else I should check before going in for a retest? Not certain on exact oil consumption, but have some.

I can't get current registration till I pass smog, and I have a sticking key in ignition issue...need the current registration so I can order a matched key lock cylinder, and don't want to start/stop the car a lot so the key doesn't get stuck and need to take apart dash...etc.

Any help MUCH appreciated! :-)

ps2cho · #2 05-17-2011, 10:40 PM

15.2 CO2 indicates you are running rich I believe....
When was the last time the O2 sensor was replaced?

Aside from that....

I suggest you go purchase an aftermarket ignition lock + cylinder for $20 and save yourself a HUGE mess if the key gets stuck!!! You can always get the matched set later, but any day now the key may not turn, or get stuck in which case you need to physically dremel out the lock shield (which is difficult -- ask me how I know...that steel is definitely built to withstand ANY attempt at theft!!!)

2wheelsoff · #3 05-18-2011, 01:11 AM

thx Ps2cho; Bought the wagon about 3 years ago...owner said O2 was "newer" but seeing what I saw after pulling motor/tranny I doubt everything he told me. I'll be starting there...hoping the cat is OK. What is a good not too lean or rich figure for %CO2?

Suggestion on aftermarket lock cylinder shop? It would really be a mess if key gets stuck again. Car is parked underground till I make a laundry list of what to fix before ging in for retest.

mbdoc · #4 05-18-2011, 08:09 AM

With the HC's at 121 you must have a slight miss.. plugs & wires most likely

OF course the vacuum leak can also cause that issue.

ps2cho · #5 05-18-2011, 12:40 PM

You want around 14.7 preferably. I'd personally get a new O2 sensor since it sounds like history is vague at best. I think 94's use the 4 wire O2 sensor otherwise I'd suggest splicing in a new one and saving yourself $60 although there may be a splice in sensor for the 4 wires too, I'm not sure.

PM'd about lock.

2wheelsoff · #6 05-18-2011, 08:30 PM

I'll pick up a generic O2 and splice it in. I think I may have a leak at the induction where the induction plumping sits on top of the valve cover for venting....can't find the gasket sold anywhere so will likely have to do a ghetto gasket with some RTV. I'll confirm the egr is working right too, though think it is. Will post results once I re smog.

tjts1 · #7 05-18-2011, 11:54 PM

Quote:

Originally Posted by 2wheelsoff

Need some people with emissions expertise to chime in please.

CA emissions failed:

Speed RPM %CO2 %O2 HC(ppm) CO% NO(ppm)
15mph 1608 15.2 0.3 121(fail .29 736(fail)
25mph 2236 15.4 0.1 32(at limit) 0.06 219

max HC = 57 at 15mph and 32 at 25mph
max NO = 478 at 15mph and 484 at 25mph

Wow they really wanted your car to fail. For comparison the limits for my 92 are:
max HC = 114 at 15mph and 88 at 25mph
max NO = 785 at 15mph and 724 at 25mph

The limits for a brand new cars are not much lower than what your car is expected to pass.
http://www.smogcheck.ca.gov/pubwebquery/cutpoints/ShowMake.aspx

As previously mentioned, try a new O2 sensor first.

david s poole · #8 05-19-2011, 12:05 PM

based on your numbers i strongly suggest that you get a cat replacement.here in texas that can be done for less than 300 installed and will make a huge diff to your readings and you won't have to sweat the little stuff which may or maynot help.the reading of 15.2% co2 means that the engine is running very well.[it's a measure of efficiency] and is one of the reasons i'm saying replace the cat.the other is the high nox.just did this on a client's car 3 days ago and then passed with flying colours.

2wheelsoff · #9 05-19-2011, 01:39 PM

Quote:

Originally Posted by david s poole

based on your numbers i strongly suggest that you get a cat replacement.here in texas that can be done for less than 300 installed and will make a huge diff to your readings and you won't have to sweat the little stuff which may or maynot help.the reading of 15.2% co2 means that the engine is running very well.[it's a measure of efficiency] and is one of the reasons i'm saying replace the cat.the other is the high nox.just did this on a client's car 3 days ago and then passed with flying colours.

thanks for the suggestion. I have access to a mig so can do the cat for little $$$ so just some labor and about $120ish on amazon of all places. retesting is not very expensive if I return to the same shop, so will try o2 first and if that doesn't cover it take care of the cat.

2wheelsoff · #10 05-19-2011, 01:45 PM

Quote:

Originally Posted by tjts1

Wow they really wanted your car to fail. For comparison the limits for my 92 are:
max HC = 114 at 15mph and 88 at 25mph
max NO = 785 at 15mph and 724 at 25mph

The limits for a brand new cars are not much lower than what your car is expected to pass.
http://www.smogcheck.ca.gov/pubwebquery/cutpoints/ShowMake.aspx

As previously mentioned, try a new O2 sensor first.

good resource... an E350 from 2007 requires has same restrictions on CO% slightly tighter restriction HC and is more lenient on the 25mph NO ppm! impressed at how clean a 94 can run.

tjts1 · #11 05-19-2011, 03:13 PM

Quote:

Originally Posted by 2wheelsoff

good resource... an E350 from 2007 requires has same restrictions on CO% slightly tighter restriction HC and is more lenient on the 25mph NO ppm! impressed at how clean a 94 can run.

Any old car can run extremely clean numbers given that the engine management and cat are in good condition. The point is that CARB manipulates the MAX numbers for each model every year to increase or decrease the number of failures. Their goal is to have about 15% of the population of each model fail every year. If you compare identical cars from different model years or different transmission you'll see completely different MAX limits.

Here is my numbers before and after changing the O2 sensor.
http://img.photobucket.com/albums/v242/tjts2/Green%20Mercedes/003-5.jpg?t=1305832370

Duke2.6 · #12 05-19-2011, 11:41 PM

See the next page for my post on the AZ emission test failure thread.

Your car will likely pass with the same slight changes.

The O2 readings indicate your catalyst was too cold. Did you "manage" the test properly?

Your CO is a little high, but that's probably due more to a cold catalyst than a degraded O2 sensor.

FWIW check archives under my handle for more information before you spend money on a new O2 sensor or catalyst, but it's your money.

Duke

2wheelsoff · #13 05-20-2011, 01:49 AM

Duke,

Your post http://www.peachparts.com/shopforum/showthread.php?t=298724

Is it strictly for the M103 or can I change the engine's response in the M104 with the same method?

thanks:-)

Duke2.6 · #14 05-20-2011, 11:10 AM

Retarding the spark advance map will lower emssions for any engine, but I'm not sure exactly how to do it on the M104 since I'm not familiar with the M104's ignition system details.

The fact that you have measureable O2 indicates that either the catalyst is too cool or it may be degraded. If the cat is hot enough to operate at peak efficiency, the O2 readings should be 0.0%. The percent O2 is a diagnostic tool, and it's important to understand what it implies. If it's more than zero it means not all possible catalyst reactions are taking place.

Duke

ps2cho · #15 05-20-2011, 11:18 AM

Quote:

Originally Posted by Duke2.6

Retarding the spark advance map will lower emssions for any engine, but I'm not sure exactly how to do it on the M104 since I'm not familiar with the M104's ignition system details.

The fact that you have measureable O2 indicates that either the catalyst is too cool or it may be degraded. If the cat is hot enough to operate at peak efficiency, the O2 readings should be 0.0%. The percent O2 is a diagnostic tool, and it's important to understand what it implies. If it's more than zero it means not all possible catalyst reactions are taking place.

Duke

So what you are saying is that the higher the O2%, the worse the cat is performing correct?

I just went back and checked my 2009 smog with my Magnaflow cat and precats hollowed out and I had 2.7% at 15mph and 1.4% at 25mph....so maybe my cat is underperforming?
The AZ test does not provide O2% unfortunately...