M103 running problems, EHA, Duty cycle, etc..

[tinypanzer]

Hello everyone,

I've been experiencing problems with my 300SE even before I bit into the heater core job, now thankfully completed. Now I have to figure out why my car is running like doo-doo.

I'm going to split up lists between symptoms, and what I've done so far.

First the symptoms:

1) Occasional cold-start difficulty and cold-start rough idle.
2) Engine lacks power until car is completely up to temperature
3) Surging and pulsing during those weak accelerations
4) Seems to be missing at idle, with varying severity depending on engine temp
5) Engine seems to lack power in the 2K RPM range (even more than a normal M103!) and when revved in neutral, shows a lack of fuel delivery or similar type slow rise in RPM around that RPM range


Here's what I've done:


Duty cycle observations:

1) The duty cycle shows 70% when engine is off an ignition is in position II and car is dead cold. By the Steve Brotherton DIY and related links, I found a chart that tells me that this is normal for this type of ECU.

2) When engine is started, Duty cycle goes to STEADY 50% immediately. The same chart means that this indicates either 02 sensor not yet up to temp., or disconnected (or completely faulty). After the car warms up for a few minutes, the duty cycle then starts to fluctuate as it should, starting at about the 40% range. Then as the car warms up further, the duty cycle slowly drops to 0%. Then the duty cycle begins fluctuating between 0% steady for several seconds, then 100% steady for several seconds.


I have not yet obtained a proper duty cycle reading of a fluctuating, yet hovering around a certain percentage reading, indicating a satisfactory closed-loop operation.




Can anyone suggest the next logical step in troubleshooting this problem? Should I monitor EHA current, or check for something more simple first? o2 sensor is Bosch universal type ordered from Phil @ fastlane and is about 1 year or so old.



** Tested & Known Good **
Coolant temp sensor good
OVP good
Alternator good
Plugs & Wires good, cap & rotor 2 years old.