KE-Jetronic issues with m103

[petrol_pyro]

Hi All

Seeking some collective wisdom on a rough idle and poor engine performance on a m103 engine. I think the oxygen sensor is the culprit but wanted to check

Basic checks of computer (test 1-3 as per https://mbworld.org/forums/e-class-w124 ... nosis.html) work fine.

So I went to test the Lambda Ratio.

Start the engine cold, on/off ratio is about 50%, but when it warms up it slowly increases to an on/off ration of 92.3% (ie measured duty cycle of 7.7%, voltage between pits 2,3 at X11 connector about 1.72v), and stops there. Measurement was taken using multimeter which could measure duty cycle and voltage.

Blip the throttle and the on/off ration returns briefly to 50%, then over the next 20-30 seconds increases consistently until stopping at 92.3%

Changes, even large ones, to the Lambda control screw make absolutely no difference to the on-off ratio.

So I let the car cool down, follow the instructions here (http://www.benzworld.org/forums/w124-e- ... sting.html) to test the voltage at the O2 sensor

Ignition on, engine off, cold: 0.5v
Engine on, cold: 0.45v
Engine on, ~40C: 0.37v
Engine on, ~70c: 0.28v
Engine on, warm (80C): 0.29v-.32v

Blipping throttle seems to make no difference to the O2 sensor, except that it drops to almost ~0.15v after you take the foot off the accelerator as the engine RPMs drop.

So my theory is the Oxygen sensor is stuffed and always reading lean, causing the computer to make the air/fuel as rich as its adjustment will allow.

Other theory could be the labda adjustment screw has been fiddled completely out of wack, so the computer can't adjust things properly.

Any suggestions on the theory, and what next steps I should take? My options are as I see it

1) Alter the lambda adjustment significantly richer (i.e 180 degrees clockwise) and see what happens
2) Replace the O2 sensor.

[Ivanerrol]

Check to see that the cat is not blocked.
The EHA maybe leaking - you need to check that.
Vacuum leaks?

The reality is that the O2 sensor is only there for minor adjustments for the emissions.

The engine should run fine without the O2 sensor being connected.

[TheMadRacoon]

Worth checking some basics.

Friend's W126 420SEL (KE Jetronic M116) recently had rough idle while cold, ie until it reached normal operating temperature. Thoughts of expensive EZL problems flashed through my mind.

Turned out to be simple: degraded spark plug (ignition) leads. Changed and all back to normal.

[petrol_pyro]

Will check vacuum leaks but seems to be ok.

Have decided to bit the bullet and buy new plugs and wires, even though it seems pretty clean. I've also checked another w124 and am pretty sure the O2 sensor is cactus so will replace that.

How do you check if the cat is blocked?

EHA testing is next stop.. seems like a fiddly PITA job so will do that after the obvious culprits are done!

Any other suggestions?

Check to see that the cat is not blocked.
The EHA maybe leaking - you need to check that.
Vacuum leaks?

The reality is that the O2 sensor is only there for minor adjustments for the emissions.

The engine should run fine without the O2 sensor being connected.

[dhaigh]

Here is a link to the Bosch manual on the "KE-Jetronic Fuel Injection system" as used on R107, R129, W124, W126 and W201 for the period (M102, M103 and M104 - early 24-valve - engines). A scintillating read of 23 pps even if I say so myself - a complete novice, but learning a lot!!
http://www.berlinasportivo.com/Technica ... ic-OCR.pdf
(Ignore the warning message you may see when you click the URL and click OK - you receive this message because the file is PDF). After the PDF opens in your Browser, you can save it to your computer. Ignore Page 1 (advertising for the site) and start at Page 2 – Officeworks will print this PDF for you, starting at page 2, if you take it to them ($7.50).
Enjoy
Here is the link to the M103 Maintenance Manual online for all the necessary measurement data you will need when testing the different injection system components of your M103.
http://w124-zone.com/downloads/MB%20CD/ ... 3-0121.pdf