O2 sensor electronics testing - PeachParts Mercedes-Benz Forum

Victor300E · #1 10-12-2007, 05:07 PM

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

Victor300E · #2 10-14-2007, 12:08 PM

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?

Arthur Dalton · #3 10-14-2007, 12:44 PM

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

Robert Squires · #4 10-14-2007, 12:47 PM

* 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.

Robert Squires · #5 10-14-2007, 01:50 PM

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

myarmar · #6 10-14-2007, 05:52 PM

Quote:

Originally Posted by Robert Squires

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

Victor300E · #7 10-14-2007, 08:07 PM

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?

190eand me · #8 10-18-2007, 08:50 PM

I hate to tell you this Victor but a o2 sensor is nothing but a low level battery...that activates when heated......test my theory by taking it out of the car ...hook it up to your VOM meter and use a propane torch on the tip and see what happens to the voltage. interesting.

and it the only way to tell if its working or not

emerydc8 · #9 10-18-2007, 09:13 PM

Thanks again, Jim. I have the rubber connector for the MAF on order. I figure that will break when I take off the MAF. I'll post the results.

JimF · #10 10-18-2007, 10:10 PM

Quote:

Originally Posted by 190eand me

I hate to tell you this Victor but a o2 sensor is nothing but a low level battery...that activates when heated......test my theory by taking it out of the car ...hook it up to your VOM meter and use a propane torch on the tip and see what happens to the voltage. interesting.

and it the only way to tell if its working or not

And you can get a feel for whether it's good or bad by testing it following the procedure in MENU#4 under "O2 Sensor Testing".

emerydc8 · #11 10-19-2007, 01:12 AM

While I am waiting for the rubber boot to arrive for my MAF, I hooked the autometer up to my car to check the Lambda. It was consistently between 48%-52%--both at idle and 2500 RPM. Does anyone know what this plug is with the numbers 052 stamped on it? It's on the right side of the engine bay.

JimF · #12 10-19-2007, 01:36 AM

Quote:

Originally Posted by emerydc8

While I am waiting for the rubber boot to arrive for my MAF, I hooked the autometer up to my car to check the Lambda. It was consistently between 48%-52%--both at idle and 2500 RPM.

That's perfect! Where did you get the connection points?? You may be able to find the connections in the 38 pin Diag Connector on pin 14 for late '94 and and on.

Quote:

Originally Posted by emerydc8

Does anyone know what this plug is with the numbers 052 stamped on it? It's on the right side of the engine bay.

That looks like the connection from the ETA via its flying cable.

emerydc8 · #13 10-19-2007, 01:53 AM

At what I think is X/11 next to the purge valve on the left side of the engine. I think my car was made in November 1992. I put the red on pin 3 and the black on pin 2, selected frequency and it came up as a %. Is that right?

Do I have an ETA? I thought my car just had the mechanical linkage. Maybe I'm confusing the two. In any case, I unscrewed the plug with the engine running and the idle increased.

myarmar · #14 10-28-2007, 05:44 PM

FYI: the old style ETA plug (90 deg) and cable is available separately from Germany very cheap (compare to ETA). If you want you could replace the cable and hope for the best. p/n 140 540 15 81. I ordered them couple years ago from Roy Tucker. http://rrparts.com/
Mike