Failing emissions! 1995 S500 Coupe - PeachParts Mercedes-Benz Forum

Trojadc · #1 06-07-2007, 12:44 PM

I have a 1995 S500 Coupe, that has failed the emissions inspection twice, here in Massachusetts. Have had the car gone through by a Mercedes Benz dealership. Only thing left to look at is the CAT...$$$. Was wondering if anyone has had similar issues, and can lend any guidance. Other than this 'slight' problem, the car is mint and runs perfect. She only has 66K on her. Your thoughts are greatly appreciated.

david s poole · #2 06-07-2007, 12:56 PM

can you provide the complete results from the failed tests as well as short descrip of test?

Trojadc · #3 06-07-2007, 01:11 PM

Auto is put on a Dyno and with a cone and some sort of probe inserted in the tailpipes. Tech watches a computer screen and increase speed based on the computer screen... Sort of like a video game. Car must stay between the lines and go up and down hills... ie have the car in gear reving to whatever will keep it inbetween the two lines. Test results HC - hydro carbons were fine...MA limit is 1.20 and it blew a .94 and a .96. NOx is the problem, limit is 2.50, first time it blew a 4.77, then i had the engine wire harness replaced. which corrected the issue with the EGR valve and the Air Pump, and the air intake sensor. Second test was much better, but still blew a 2.69. Which is a bit over the legal limit of 2.50. thanks for you help

Trojadc · #4 06-07-2007, 01:13 PM

Oh and CO was fine..Limit was 20.00 and it registered a 6.96. All results are measured in Grams Per MIle

mbdoc · #5 06-07-2007, 01:48 PM

NOx being too high ON that car is either a result of low EGR flow or a bad catalyst.

I would make sure that the EGR system is fully functional. And that the EGR tube isn't partially plugged.

Trojadc · #6 06-07-2007, 01:53 PM

how does one make sure the EGR system is fully functional and that the EGR tube is not plugged. The car was serviced at an MB dealership out of Tiverton, RI. It went in specifically for he emissions problem, and from there testing, I was told that everything was functioning properly.

david s poole · #7 06-08-2007, 11:36 AM

with the fact of the hc being so close to the mark[upper limit] and the nox being so far over and the co being relatively low.i would say that you are running lean[not enough fuel]the highish hc will be due to misfires from lean condition and that means plenty of spare 02 for the creation of nox.do you have the 02 readings?sounds like they are running a hot 505 epa test.

Trojadc · #8 06-08-2007, 11:55 AM

by O2 reading do you mean CO2 in grams per mile?? that reading was 509.62. Thanks for helping....Much appreciated!

david s poole · #9 06-08-2007, 01:02 PM

no i mean the oxygen readings.

Trojadc · #10 06-08-2007, 01:36 PM

No, unfortunately, I do not... But does this help... the car sat from end of Oct '06 to May 23rd '07 with only 40 miles put on her. Maybe it just needs some good running the Highway for a bit, to blow out anything? Regards
Andy

david s poole · #11 06-08-2007, 01:42 PM

you may very well be correct.at least get that old gas out of it.oil change wouldn't hurt prob got some gas contamination.

Trojadc · #12 06-08-2007, 02:39 PM

Gas has been done, oil change done, the dreaded wire harness done, and completely gone through by a reputable, strictly MB dealership in RI. Their thought is the only thing left is Catalytic convert... I am just trying anything else i can, before making that kind of $$$ commitment!

Arthur Dalton · #13 06-08-2007, 03:57 PM

On a car that sat that long and only has had a few miles out on it since, I would want to try a good, hard run using a lower gear range , preferably up hills to create as much of a load as you can..that will clean that cat out.
Then drive a few normal drive cycles to have evertying adapt back to normal..You wiil know if the cat is cleaning b/c you will smell rotten eggs.
A cleaned cat and o2 sensor may just do it....check the air filter while you are at it...
Try it before motgaging the house..

Trojadc · #14 06-08-2007, 04:11 PM

Arthur,

Thanks for the advice. I will try that.. like i said in my original post..the NOx limit is 2.5 and it blew a 2.69, so it can't be off by much. How many hills should I do.. and for how long? Is that going to hurt the engine? Many thanks Andy

Arthur Dalton · #15 06-08-2007, 05:53 PM

How many hills??? How long ???
aw , lets see,, if we have a hill with a slope of 12 degrees and dry pavement , 1.3 km long, at 4K rpm, we can...yadayada ..

The IDEA is to get on it and heat the cat to burn off the debries and get the cat back in shape...that's all.
..and you use the lower gear so you can get the R's up there without speeding..and the hill is to put a load on the engine ..might not help you at all. but I would try it first....