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Old 11-02-2003, 10:36 PM
stevebfl stevebfl is offline
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
In normal convention a 45% duty cycle represents a system that has used up 5% of its correcting ability to lean out a 5% too rich calculation.

What you have to realize is that any percentage exhibited in closed loop creats the same mixture. Try very slight pressure on the airflow plate. You are richening the mixture. Watch the duty cycle. It will go lower and lower until the resulting mixture is back to closed loop control. It will do that within its capability or about from the range 10% to 90%.

So, if you turn the allen adjustment the system compensates... always keeping the actual mixture going into the engine the same.

The point to setting the car a little rich (45%) is that although closed loop mixture is the same, open loop mixture is richer. Open loop is all cold running, full throttle and non steady state operation (sudden acceleration).

Now that you are adjusted, you need to see if the problem still exists. It probably does. The next step would be to watch the duty cycle during the event and preceeding. You are more likely to need a fuel pressure gauge. If you are running out of fuel due to say a weak fuel pump or restricted filter, you could see the condition as it unfolds using the above technique. As the pressure dropped and the mixture dropped the duty cycle would go off range way before any actual symptom was felt. Actually the system doesn't react as fast as problems can appear, but within seconds of a fuel pressure related mixture change the system will correct or run out of room trying.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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