M117 how to test lambda? - PeachParts Mercedes-Benz Forum

LandYaghtLover · #1 01-09-2011, 10:10 AM

I thought I was given a link on this, but can not find it. So I searched and searched, but I did not locate have the procedure or even have a clue on how its done. I know whats needed, just not sure where to plug stuff in and such.

Guess I am just a lot more used to re-flashing the cars ECU

timmyr · #2 01-09-2011, 06:44 PM

hey LandYaghtLover,

you're researching oxygen sensor testing instead of watching the packers?! shame on you

i think ps2cho recently posted the procedure, ill post it if i find it.

is the M117 oxygen sensor a 4-wire sensor like on the M104?

if it is then maybe this old post by Arthur Dalton can be of use:

Finally , I doubt you have an 02 sensor problem , but they are fairly easy to test on that model b/c it is full electronic engine management.
Under the passenger rug is the 02 wires. The green one gets unplugged so that no sig goes back to ECU . Now , the blk wire that plugged into the green is 02 sensor output. You can connect a DMM + there and a good ground.
Now , with engine @ temp and a decent idle, watch your meter as you remove the vac line to the FP regulator [ cap the line with your thumb so you don't create a vac leak while doing this test].
This will make the reg increase the FP and that increased pressure will cause a manually induced RICH condition to the engine and will show right up on the 02 as a high voltage [ .8-9v].. That is the rich test for 02. The engine can not correct for this b/c it does not have an 02 input sig. going back to the ECU b/c you disconnected the green wire..
Now , hook the vac line back up to reg and then take a good sized vac line OFF somewhere and watch your meter go LEAN..[ .1-.2 v].. That test 02 ability to read LEAN condition....now , to test the switching speed , I take that line you are using for the lean test and put my thumb over it , on and off, while watch the DMM..it shoud react to your on/off input of air through that vac line pretty fast. If so, you have a decent 02.
A scope pattern is much better, but this is a viable DIYer test on HFM systems..what you are basically doing is using the engine as a Lean/Rich generator and simply seeing if the 02 has the ability to react to you manually causing a rich or lean condition.

good luck

LandYaghtLover · #3 01-17-2011, 03:58 PM

Found a neat write up that uses voltage at the test port. #2 & #3 pins. Voltage should read around 12.3/12.3 apparently. Higher voltage (13v)=rich and lower=lean. This is with O2 unplugged, engine up to temp.

Anyone ever try this method? I have only seen it mentioned once now.

JamesDean · #4 01-17-2011, 04:17 PM

http://www.landiss.com/mixture.htm

LandYaghtLover · #5 01-17-2011, 05:22 PM

Quote:

Originally Posted by JamesDean

http://www.landiss.com/mixture.htm

Awesome. Thank much!

LandYaghtLover · #6 01-18-2011, 10:41 PM

Well I was running at 6.94. Rather rich as suspected. Adjusted full 180 and did not get results as expected. The car is much slower to react than I thought it would be. After a while (driving) it was running a little rough. Read 0.27! So adjusted some more and got it to 4.3 volts. Good enough for now. I suspect the engine was not warmed up enough when I made my initial adjustments. It was very, very cold out.

Results are a slightly more responsive throttle. Much more "power". The idle is incredible smooth now.

Per the link above: I did not remove the tower. Mine was already "cracked" apart to remove the tamper device.

Thanks much. Very happy and I suspect my fuel economy will greatly improve.

Hirnbeiss · #7 01-19-2011, 02:03 PM

Note that old (high mileage) O2 sensors are slower to respond (I'm not sure how noticeable it would be in your case), but that is the reason for the 2nd sensor on later model cars after the cat. It sends a signal to compensate for the delay on older sensors.

LandYaghtLover · #8 01-19-2011, 02:19 PM

The O2 I have looks like a fresh install. But I am going to replace it soon anyway due to the car running rich.

As for the second sensor after cats. As far as I know its there to make sure the cats are doing their job. Thats all. Many times in the forums the upstream is recommended to be replaced at regular intervals but the downstream only when a code is thrown. I even see this when I write programs for cars. Front O2s have variables, rears never do. Its also why the upstreams are heated and the rears usually not - no need.

LandYaghtLover · #9 01-26-2011, 08:13 PM

Just an update. After another adjustment things are looking pretty dang good! Average just over 19mpg. That was about 90% highway. So I am very, very happy with that!