Smog check caught up with me
 

I have a 1991 300CE with about 150m and I've put up with a rattling cat over the past several years. At each successive smog test, I'd make sure the engine was good and hot and kept my fingers crossed. Since the rattling started, I think I passed 2 tests (every 2 years) but now finally failed one and here are the results:

-----------CO2-----O2------HC max/meas-----CO max/meas-------NO max/meas
15mph----14.50----.07---------106/18----------.70/.04-----------762/1082 failed
25mph---- 14.50---.08----------81/14-----------.57/.02-----------701/1044 failed

From other threads, it looks like could be the EGR valve or most likely a new cat is needed, both expensive.

Any help in narrowing this down?

Thanks,

glenmore
1991 300CE
2000 C280
1990 LS400

Based on your numbers, I do NOT believe the cat. conv. is the problem.
Focus on the EGR, as it is mostly responsible for NOx. ;)

Yeah, as Manny said, it looks more like an EGR fault. The HC numbers would be affected by a failed cat, whereas NOx is almost entirely the EGR system.

If you got ambitious when you're under the car some time, you might unhook your front section of exhaust, with the cat in it, and shake it upside down, see if anything falls out.
I found a bolt in an old car's exhaust... HOW someone managed to dump a bolt down the front end of the exhaust, I have NO idea, but it had done a good bit of damage to the front end of the cat, bouncing around in there!
I won't say you have one as well, but you may have small chunks of some sort of debris that could be dumped out.

300CE is very sensitive to Smog tests in my experience
 

My 300CE would not pass the Smog test in Dallas; had to take it to the Fort Worth Dealer where I bought it and they adjusted the engine so it passed. It was always running well and with full power, but I ran some good injection cleaner directly through the engine and some other stuff thru the air intake and it runs even better. I will certainly look at the EGR system before the next test is due in 08. Ben Carter

Haven't gotten my car back from the shop but here is the breakdown.

After not passing at a Test Only Station, they alerted me to the Consumer Assistance Program (CAP), funded by all of us California taxpayers. You can get $500 of repair assistance from being Income Eligible or Test-Only Eligible. I qualified under the Test-Only criteria. You send off an application to Sacramento and they spot you $500 for smog repairs IF there is $$$ still in the fund. Lucky for me then that my test was early in the year. You get a long list of approved repair stations that you must select from. I made quite a few calls and they were not encouraging. A lot of the shops were corner gas stations. I got lucky and called a Honda/Acura only shop who then referred me to a nearby shop that sounded good. The shop was neat, filled with cars, AAA approved, ASE everything, and one thing I always like to see, big SnapOn tool chests.

I talked with their smog fellow and he seemed to be familiar with MBZs. Here is what he discovered:

Testing the EGR valve with vacuum showed it leaking/failing. The results of a second smog check showed much worse NO numbers than the original test. No change to the idle so the tube was clogged also. The solenoid switch that activates the valve was also faulty. Total repair about $820. There is a $100 co-pay, so I pay a total of $320. They were able to get parts at reasonable prices, $275 for the valve and $67 for the solenoid and they will just clean the tube.

I initially thought that this program could turn out to be a big boondoggle for all these repair shops to inflate repair costs to "use" up the initial $500 and then keep charging but the guy said that before going ahead they must lay out the repair plan for Sacramento approval, so there is some oversight.

When I mentioned I had recently just replaced the O2 sensor he said that might be a problem particularly if I used generic and just crimped the connections. My repair was OK but he said they have seen problems with generics unless the connections were soldered. He said that these sensors operate at such low voltages that OEM connectors without splices were best followed by a good soldered connection.


glenmore
1991 300CE
2000 C280
1990 LS400

Interesting that you mention that the pros recommend soldering the generic O2 sensor...I was considering this but this area gets so hot I was wondering if the solder might actually melt. Those wires coming off of the sensor are teflon-insulated, by the feel of them. Properly done crimped connections with the right tools and supplies can be as good if not better than solder.

I was also wondering where CA is getting all this money from, considering that its apparently going broke?

Boy, that sure takes the sting out of forced car repairs.

based on your numbers your car is running too LEAN.you have too much o2 left after combustion and the co numbers are too low.i have my doubts whether the egr valve in benzes operates at all at those low rpm's.richening up the mixture should make the car pass.

Even the best crimped connections are eventually affected by oxidation(and therefore increased resistance). I prefer use solder, shrink tubing and minimize the chances of the joint causing problems in the future.

Here are the results of my passing test after the r&r on the EGR system:

-------------CO2-----O2------HC max/meas-----CO max/meas-------NO max/meas
15mph----15.2-----.1---------106/12----------.70/.02--------------762/176 passed
25mph----15.2----0.0----------81/9-----------.57/.02--------------701/166 passed

Labor and parts for the repair weren't too bad. The expensive part was the $193 for diagnosis.

glenmore
1991 300CE
2000 C280
1990 LS400

Wow. Cleaned up well. Congratulations, and it didn't cost you a cat.

Are you still running on the original on or has it been swapped out with an after market?

Tinker

So it you fail the test you quailfy for program if theres money? Is money allocated monthly or anually? Guess it is best to test in January if it's anually. I know in Virginia there a limit wavier. That is if you spend like $500 to try to pass and you still fail you get a waiver and you can still drive.

add 3 ounces of acetone per 10 gallons of fuel.
http://www.pureenergysystems.com/news/2005/03/17/6900069_Acetone/

I believe the cat is original. The rattle from the cat is small, you can only hear it over bumps with the passenger window down. I'm hoping whatever is loose/broken will not progress to total failure. Keeping fingers crossed!

glenmore
1991 300CE
2000 C280
1990 LS400

I've found from my experience that many times the rattle is not from the honeycomb structure of the cat, but rather from the heat shield.