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  #1  
Old 07-28-2003, 11:39 PM
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Location: Colorado Springs
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Duty cycle

I have a quick question. I have recently set my duty cycle at 70% the engine is smooth as silk and idle is excellent. However, this is a bit lean. Am I doing any damage to the car, I live in colorado at 6000 feet and they do use ethanol in the gas too(10%). Any advice apreciated.
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  #2  
Old 07-29-2003, 08:49 AM
LarryBible
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A lean condition is very BAD for engine health. In a lean condition combustion chamber temperatures SOAR. This can lead to burnt valves, piston melting and all sorts of things.

I don't remember if high duty cycle is lean or rich, but if it is lean, I am shocked that you have good power.

My $0.02,
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  #3  
Old 07-29-2003, 09:07 AM
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Remember this, whenever the engine is in closed loop (duty cycle active) that the mixture is always the same except at full throttle! That is the reason for Lamda controls. So whether you set the duty cycle ay 20% or 70% the computer keeps the mixture the same.

However durning warm-up & at full throttle (open loop) when the duty cycle is adjusted on the lean side then the fuel mixture will also be lean!!
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  #4  
Old 07-29-2003, 09:09 PM
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Thanks for the advice, reset it back to 48-55%.
m
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2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)
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  #5  
Old 07-29-2003, 11:24 PM
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Join Date: Mar 2003
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Lightbulb

M.B.DOC, i have not seen this stated this way before. i did a search on "duty cycle" and your reply took on new meaning. it appears that fuel mixture should be adjusted during open loop since the 02 sensor attempts to keep it there during closed loop. is this reverse logic correct? charlie
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  #6  
Old 07-30-2003, 08:30 AM
LarryBible
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Yes, MB Doc not only has scads of MB experience, but can also articulate it very well. He is greatly appreciated by all.

Have a great day,
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  #7  
Old 07-30-2003, 09:09 AM
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Duty cycle OR Lamda(14.7/1) fuel mixture is designed to keep the engine from emitting excessive emissions. Open loop fuel mixture is important however there really isn't any spec for that type of setting anymore. IF you set the mixture too rich OR lean in open loop then the O2 sensor MIGHT not be able to bring the car into closed loop, or the system might go into FOM (fixed operating mode)

That is why MB suggests a duty cycle of 50% +- 10%
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  #8  
Old 07-30-2003, 01:26 PM
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To moneypit:
The MB manual states the Duty Cycle MUST be adjusted at Normal Operating Temperature - Read Closed Loop

DO NOT adjust Duty Cycle on a cold engine (Open Loop).
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