O2 sensor electronics testing
 

Hi guys,
I have 1992 500sel.m119
I understand that oxygen sensors put out 0.1 to 1 volt of DC depending on the exhaust fumes. Now if I disconnect O2 sensor and connect 1volt battery to terminals that go to computer will you notice the difference in engine sound? I suspect my computer to not working properly as I connect the 1volt battery to O2 terminals I hear no difference in engine sound, it would run the same as O2 sensor connected or not or 1 volt battery connected or not. Does that make you think that computer went south?
Mechanic pulled codes. Idle switch on gas pedal and starter lock out/back up switch on the transmission came up. I have both checked with ohmmeter and they both work fine.
Any ideas what is happening with my car?

Thanks

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?

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?

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.

I went to Jim's website and built home-brew code reader to pull codes. It works great! Thanks for your time and effort to create and maintain your GREAT website Jim:) I have found lots of info I've been searching for on it.

There were many codes found. Mostly because I never cleared them after engine harness was replaced. All of them are cleared now and I will drive the car to see which codes will come back.

I was checking my lambda and it is still in 75-85% range. It gets to the point when you hold 2000rpms you can hear that the engine is slowing down a bit when readings reach 89% and when readings drop to 75% engine picks up rpms again. Can adaptations be a cause of it? I never got code#19 of on pin 19 though. Maybe I will order new eprom just in case. I don't think that my mechanic has that scanner. He has similar looking code reader he used to pull codes with but home-made blinking code reader pulled way more codes.

I have found my purge valve inoperative so I will replace it. Lambda was checked with purge hose plugged.

Fuel pressure regulator check did not reveal anything. I had it removed and cleaned. It looked good and held vacuum.

Air intake sensor was changing value when I blow into it. It reads around 1.7kohms at 70 degrees. Coolant temperature sensor is also in correct range.

Can someone tell me what signal get to pin 40 of Base module? I suspect Base module to be either rebuilt or tampered into. I opened it and found scratches on one diode and pencil marks on the other side.

Thank you for help, guys:)

Update: I just drove the car few miles and have duty cycle checked. On idle it stays at steady 68.9% and when you keep 2500rmps it jumps from 42 to 55%.
From what I understand D/C always has to be around 50% on either idle or 2500rpms. Does it prove that my adaptation values are out of limit even though no code19 is not present?

Victor300E, did you clean the MAF and IAT as shown in MENU#4a

Hi Jim,

If checked the price of the on/off lambda ratio tester (M0039) and it was kind of expensive ($355). Any cheaper alternatives to this tool--like at Radio Shack? Nothing's wrong (that I know of), but I was going to check my ratios out of curiosity. Thanks again for all your time and information.

I've not done this but a "meter" that does duty-cycle should work ok.

My comment in the previous post was meant for Victor300E to clean the MAF and IAT. Then check the lambda . . . . he may be pleasantly surprised! :pleased: