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Old 11-13-2003, 04:39 PM
Registered User
Join Date: Jan 2003
Location: Dallas
Posts: 750
The evil lamda control

My '91 300SE exhibits lean condition on warm startup.
It chugs and struggles for a couple of seconds, then smooths out and runs fine.

-I checked the EHA current - approx 7ma at idle.
-I checked terminal 3 on the round connector with a voltmeter (my old dwellmeter died). Approx 3 volts, which indicates approx 75% duty cycle - it's adding fuel, correct?

So... it seems I am indeed a bit lean on the base setting.
But the 02 sensor is correcting when it comes online.

I assume it's time, after 13 years, to adjust the Lamda screw a bit. The motor runs great, but has exhibited this warm-start stumble for about 12 years - so maybe it was always set lean?

Does my analysis seem valid?
should I look for another problem before I jump on the Lamda screw?

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Old 11-13-2003, 05:48 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Use the EHA values they are representative. Seven milliamps is additive correction for a lean mixture.

I'm not sure on your modle but the duty cycle of late model KE cars doesn't register untill you trigger the impulse code. If the duty cycle stays the same when you place a finger on the airflow meter then this is the case.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 11-13-2003, 06:09 PM
Registered User
Join Date: Jan 2003
Location: Dallas
Posts: 750
Steve, thanks. I read your DIY post, very helpful.
so I will assume, if nothing else is wrong, I should aim for EHA values closer to 0, and tweak the lamda screw a tad CW to see if I can drop that 7ma reading down a bit.

I assume also that if I do that, then the warm startup mixture will be a bit richer, and all my problems will be behind me.

I'll try checking the pulse-width signal as you suggested.
I hope I can use that approach for general checkups of the
system - it's much more convenient than the EHA check.

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