HELP! 1990 300CE failed Texas emission test - PeachParts Mercedes-Benz Forum

Texholdem · #1 02-10-2010, 11:22 PM

Yesterday I was happy to be able to get my lambda A/F ratio to voltages between 5.9V and 7.1V, what translates to 0.56% - 0.47% duty cycle. However the numbers are for idle.

Today I measured at 2500 rpm and got reading under 3V at pin 3 of the X11 connector, which means the engine is running too lean, I tried to make it a bit richer and got the following:

Idle: 6.91V - 7.75V (0.493% - 0.42%) borderline of running rich
2500 rpm 3.02V - 3.86V still too lean

The idle reading should stay within 10% of the 2500 rpm reading, now they are way apart, I cannot bring them closer with lambda adjustment alone.

Idle: rich, 2500 rpm: too lean, that does not make sense. What is wrong? what should I look at?

Please help!

Edit: How to adjust lambda A/F ratio according to Bronzeross

Quote:

Originally Posted by BRONZEROSS

... u need the car at normal operating temp. find ur lambda connector, (shown in the first pic.) its on the driver fender well above the ignition module. find pins 2-3. using ur dmm positive pin in the number 2, and neg in pin 3. set dmm to dc volts. with the engine running watch the voltage, should ocillate from 5.5v to 7.5v. turn the lambda tower screw clockwise to richin, counter to lean. also it doesn't take much when ur turning the screw. after u do that snap the throttle and watch ur readings. also u can tell if u have a bad o2 sensor this way too. if the readings are slow or go open. that means ur o2 sensor is probably bad.

A statement from the adjustment instructions at
BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT

Quote:

Remember that if the oxygen sensor is doing its job and the system is operating closed-loop, the reading will jump around, so you might see readings from 5 V to 7 V and have guess at an average.

My reading oscillates between 5.9V and 7.1V (yesterday before enriching it to 6.9V - 7.75V), so I assume that the oxygen sensor is still OK according to the above.