Help please.. Won't pass NC emission inspection.. Where to begin???? - PeachParts Mercedes-Benz Forum

jay3000 · #1 12-31-2002, 05:30 PM

I just recently bought this car..It had several things wrong with that I have already fixed (unrelated)..

I've replaced the spark plugs, dist. cap, rotor, and air filter, and O2 sensor with one for a 90 302 mustang.. It's running on Premium unleaded.. The engine runs like a dream.. I don't know how it could run better..

I went today to have it inspected, and it FAILED the emissions test with flying colors..

HC 474 STANDARD IS 220
CO 6.33 STANDARD IS 1.2
CO2 11.0

Can anyone guide me down the road to acceptable emission readings???

Thanks,
Jay

#2 12-31-2002, 05:47 PM

Carbon Monoxide is a product of incomplete combustion caused by lack of air in the air/fuel ratio.

Your car is running rich. The high Hydrocarbon reading is unburnt fuel because the engine is not running efficiently.

I would sugest you first try and weaken the mixture.

If you have access to a three gas analyser you want CO as low as Possible, HC as low as possible, CO2 as high as possible, (14.6 being ideal)

Good luck

RDA

jay3000 · #3 12-31-2002, 06:27 PM

The people where I went to get the inspection done think that replacing the catalytic converter was my best bet.. Are there some adjustments I can make to change the fuel mixture???

I'v only had it long enough to use one full tank of gas.. 18.5 mpg, some city, and some rural driving, very little highway..

BTW the thermostat is new too.. The temp gauge reads a little above 80C..

Thanks,
jay

mhingram · #4 12-31-2002, 06:37 PM

Jay where in North Carolina are you
martin

jay3000 · #5 12-31-2002, 08:50 PM

Quote:

Originally posted by mhingram
Jay where in North Carolina are you
martin

Greensboro area...

I'm the guy driving around in the beautiful 300SEL that's killing everyone..

Ken300D · #6 01-01-2003, 01:22 AM

Does an oxygen sensor from a Mustang work properly in a Mercedes?

Yes, I understand that clean combustion should be the same in either car, but perhaps the sensor would be calibrated differently. That is, the signal the computer would expect.

To give a rough example, perhaps the Mustang computer expects a 5-volt signal from the O2 sensor, and the Mercedes expects 10-volts when burning clean. Use the wrong sensor, and your computer thinks something is wrong because the calibration is different.

I'm surprised it would even fit in your car. Are we talking about the sensor that normally threads into the exhaust pipe somewhere?

Ken300D

Richard Wooldridge · #7 01-01-2003, 02:35 AM

Hi there,
Why didn't you use the correct O2 sensor for your engine? Is it possible that the engine never goes into closed loop mode? It might be running on the default settings, which means that it would be running rich all the time, as your test data clearly shows. (I could be off base here, not familiar with your engine management system, but that's the way the setup in my '82 works.) A new catalytic converter would just hide your problem for a week or so, then it would become fouled and fail. You need to find the cause of the excessively rich operating condition.
Here in Washington State they test at idle and at cruise. They used to use a dynamometer to load the drive train at cruise, but have recently discontinued that part of the test, and just run the engine at 2400 rpm now. If the engine is running properly, it will pass both tests easily.
Good luck with it!

Richard Wooldridge
'82 300D/4.3L V6
'77 Jag XJ6L
'77 280Z
'89 Astrovan
'94 Ford Taurus
'85 GMC S15/87 Firebird engine
'65 Clark Cortez/'78 Caddie 425CI engine, FWD drive train
(currently licensed vehicles only)

stevebfl · #8 01-01-2003, 10:43 AM

Obviously the feedback controlled Lambda system isn't working. Six percent CO is terrible. It would be unthinkable coming from the engine, let alone coming out the tailpipe after the cat.

The system is based upon the o2 sensor and proper set up. There are basically two different types of sensors and I presume the Ford one you chose was of the right type. Its probably not the sensors fault. The first way to test it would be to disconnect it and test the exhaust. If the sensor is grounded it could drive the mixture at the outlet to maybe 6% but the basic mixture setting (this car must have this done properly, the system doesn't do it like the adapting systems built after CIS). The system is usually adjusted electronically (see the DIY article on evaluating engine controls) but since the O2 sensor is fouled at least here, one must get back to basics.

I would disconnect the sensor, set the mixture with an exhaust gas tester to 0.5% to 1.0% CO, drive the car hard, retest and then reconnect the O2 sensor and see what happens. It can be watched electrically for evaluation (see the article).

jay3000 · #9 01-01-2003, 10:50 AM

I thought it was the general consensus of this board that the Mustang 302 sensor was exactly the same with the exception of the connector???

I've read that here, and on several other forums.. Maybe that's the problem.. Sure wish there was some way to figure this out at home..

Anyone want to buy a 300sel that looks and runs beautifully, just won't pass inspection???? Cheap...

Jay.

joe p · #10 01-01-2003, 10:54 AM

Do you ever get to the Raleigh area?

Sounds to me like the base co is just too high. Pretty simple tweak with a DVOM.

(plus you can see if the O2 is working right as well)

Joe

stevebfl · #11 01-01-2003, 11:03 AM

Come on... lets fix that car, selling it is a cop out.

While I would never advise using a Ford sensor in a MB, I do not believe it is your problem (directly). It will not be the problem unless it is either defective or possibly you have come across a different Ford application. The type of O2 sensor MB uses is very standard, the only for sure different types I know of are in Jeeps and BMWs (the 5v reference type). The japanese use some other types including a conceptual change on new Toyotas - no feed back cycle.

The reasons I wouldn't use anything except the specified sensor have to do with life expectancy and speed of performance. The sensors don't work until very hot and the design of the sensor airflow facilitates its use in specific exhaust locations. This performance deficiency possibility IS NOT your problem. YOU HAVE A GROSS ERROR.

mhingram · #12 01-01-2003, 12:44 PM

jay3000,
I would recommend you spend the money and get it looked at by a shop that has the right equipment. I know an excellent guy in west raleigh His name is dave and he owns 'The Foreign Service' here is the web page. http://www.theforeignservice.com/index.htm
I t also looks like Joe P is in Raleigh too you might want to ask him as well.

Richard Wooldridge · #13 01-01-2003, 01:25 PM

Hi again, Jay3000,
Like I said in my earlier post, I'm not familiar with your engine management control system, but Stevebfl absolutely is! Take his advice to heart, he knows what he's talking about!!
Good luck,

Richard Wooldridge
'82 300D/4.3L V6
Etc...

jay3000 · #14 01-01-2003, 06:38 PM

Looks like this is a case for the fellas with the right equipment.. I really don't have time for a crash course in Mercedes engine management, nor do I have a way to test the exhaust even if I did manage to solve the problem..

Can anyone recommend a good shop in Greensboro?????

A DIY guy has to be able to recognize the limits of his equipment, and knowledge...

Thanks for all of your collective knowledge.. I'll have more questions soon..

Thanks...
Jay..

Find me a good shop........

congonatty · #15 01-01-2003, 06:55 PM

yes, best mercedes repair shops in greensboro are carr industries on orville wright road, foreign accent on market street, european accent on vandalia road or korman automotive group on randleman road.