I have tested my O2 sensor with better ohmmeter and readings came up to be normal. I also have my duty cycle checked and it was oscillating up and down a bit so I assume lambda system is working. There is one problem: engine runs rich. I get 72 to 82 percent duty cycle reading on either idle or 2500rpms. O2 sensor readings are from .2 to .8 volts and it gives out high HC reading at inspection on idle.
I used to have 2 other MBs where I could adjust mixture with long octagon key through air/fuel meter in the middle of the engine. This car has m119 and air/fuel mixture is adjusted by computer. Does anyone know how to bring my duty cycle to 50% again? What causes the computer to run rich mixture?

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1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

Check Reg for fuel evidence at vac port.

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=21H0MN3YU27C0R8G5H&year=1992&make=MB&model=500-SEL-002&category=C&part=Fuel+Pressure+Regulator

* You've probably checked the fuel pressure, the coolant temp sensor, and the intake air temp sensor values.
* What do the adaptation values tell you? Is the fuel management really trying to correct an over-rich condition? Would corroborate the HC values.
* Beckmann Technologies will test your controllers for a small fee if you suspect, but can't prove, a problem there.
* On this site, have you checked this out. Go to DIY Links (see the tab at top of page). From there go to DIY Links by Parts Catagory. Posts are organized by relevant "parts area". You might find something useful in "fuel injection". Good luck.

Never mind the adaptation values. My mistake. Somehow had the idea your MB was later model.

It does have adaptation values. You need a scanner with live data capabilities to get them.
Mike

Thanks for replies guys.
I will check my fuel pressure along with intake temp. sensor next. I replaced coolant temp. sensor already.
I would love to check adaptation values. Where can I find a scanner to get live data capability? Is it expensive?

__________________
1999 ML430 Silver 135k ml
Smoked LED taillights, Alpine in-dash DVD player, 12" sub, Pioneer components, 2 amps, 4200k HIDs, ML55 headlights, 20" rims, mirror LED blinkers

SOLD. 1996 E320 145k ml. Burgundy

SOLD but miss it everyday 1992 500sel Black
Chime buzzer mod,Alpine CD/MP3 player with stock amp,Euro headlights,S600 grill,20" rims, BEST CAR EVER!

SOLD. 1990 300E White
187k ml,smoked tails,Euro headlights,17rims,Intake,12" sub in first aid kit,alarm/autostart,buzzer mod

Yes Victor, it is expensive. I have a Snap On MTG 2500 and Mercedes cartridge. Ebay is a best source now. Here is one for example.
MB cartridge:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=330087276384
And the scanner from the same guy:
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=330174183204
I remember paying about the same for the cartridge from Snap On and much more for the Scanner, but it had cartridge for Domestic cars.
Mike

* If you have a good working relationship with an independent shop, and can talk with their MB tech, describe the values/interpretation you're looking for and pay them for some diagnostic test time. Of course it's not easy to find a shop that will take an honest interest in your project, and even harder to find a shop that will let you past the service writer to talk with a tech.
* A tool that will do live data, some coding, as well as scanning and other functions will likely cost you at least $3K. And that's a lot to spend for just the occational test on your own car. My PC Retriever (Assenmacher Specialty Tools) was around $2500, but I got a discounted price and I already owned a multiplexer which would've added $1K to the cost. Baum Tools has a nice tool also, but it's expensive too. Be wary of cheap equipment. Comparison shop. You might be able to find a reliable used high quality tool on eBay, or from a member of this site. Good luck.

When I read that you have a 119 and it is running rich, it reminded me of something I read on Jim Forgione's site about DTC #19. http://pages.prodigy.net/jforgione/MB_S500.html

Maybe your car has not reached the adaption limit to set off the CEL, but it may be worth scrolling down towards the middle of the above link for some good information about DTC #19. Good luck.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles