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Old 04-06-2005, 06:26 PM
LeaUK LeaUK is offline
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Join Date: Feb 2003
Location: UK - South East Coast
Posts: 864

closed loop systems often cause headaches...

Sorry, I'm not making myself clear.

Is the signal at the diag connector simply a buffered version of the O2 sensor's o/p? I think it's not. I've read Duke's comments again and he says
The duty cycle is a synthesised signal that measures the relative amount of time that the lambda system spends adding a rich or lean bias to the basic mixture provided by the air flow sensor and mechanical section of the fuel distributor and is used to make any necessary mechanical mixture adjustments to keep the lambda system near the mid point of its control authority range.
You see, the system will try and meet the 14.7:1 ratio by richening or leaning the open loop mixture. If you measure the O2 sensor it should fluctuate around 50% at all times, whether you have air leaks, or a rich system or not -because that's what the system tries to achieve, 50%.

I still don't understand how to interpret the duty cycle from my pin 14 (on-off ratio) X11/4 diag. Duty cycle is the ratio of logic high to logic low but Steve B's scope is clearly measuring the opposite

Please come back Duke...

'93 R129 500SL-32
'89 190E 2.6 - sold in 2002
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