Using Oscilliscope to Set Duty Cycle

[Funracer]

Originally Posted by AndrewCologne

Set the duty cycle at idling to approx. 55%, that correspondents to approx. 0,6% CO at idle at 50% duty cycle.

As your system does regulate the mixture via sensor input and duty cycling, a leaner mixture will be avoided anyway, no matter if you set the duty cycle at idling to 42, 55 or even 65%, cause the resulting duty cycle will keep the output after combustion at lambda 1.

The only advantage of a "lower" duty cycle than 55% at idling is that when the duty cycle switches to acceleration state (65%) it will actually result in a higher AFR/lower Lambda as if it would be set to 55% at idling.

Are you saying, with black oscilliscope clip to green test plug wire, and red oscilliscope clip to ground, duty cycle should be set to 55% at idle? I have read other threads that say 45% is the number and not seen anyone use 55%. Unless the red/black probes are reversed.

Just looking for clarification
Thanks

[Damon88]

Mine is now set at 55% with BLACK to green wire on test port & RED to ground. If I reverse this I have a reading of 38% Duty. Can any one confirm what is the proper hook up procedure. Cheers

[AndrewCologne]

Originally Posted by Funracer

Are you saying, with black oscilliscope clip to green test plug wire, and red oscilliscope clip to ground, duty cycle should be set to 55% at idle? I have read other threads that say 45% is the number and not seen anyone use 55%. Unless the red/black probes are reversed.

Just looking for clarification
Thanks

From the tests I did, 0.8% CO at Open Loop DutyCycle 50%, does correspondent to approx 55% at Closed Loop at lambda 1.

[Funracer]

Originally Posted by AndrewCologne

From the tests I did, 0.8% CO at Open Loop DutyCycle 50%, does correspondent to approx 55% at Closed Loop at lambda 1.

Andrew you have to dumb this down for the rest of us.

With black clip to green wire and red to ground, what duty cycle are we looking for at 1000 rpm idle?

Apologies

[Damon88]

Originally Posted by Funracer

Andrew you have to dumb this down for the rest of us.

With black clip to green wire and red to ground, what duty cycle are we looking for at 1000 rpm idle?

Apologies

Took the works out of my mouth..haha thanks Funracer.

[AndrewCologne]

Originally Posted by Funracer

Andrew you have to dumb this down for the rest of us.

With black clip to green wire and red to ground, what duty cycle are we looking for at 1000 rpm idle?

Apologies

At 900 rpm swinging around 55% duty cycle at closed loop, means with OX sensor plug connected and therefore lambda regulation active.

This does correspond to approx 0.8 % CO at 50% duty cycle with sensor disconnected, means open loop for doing the test with a CO measuring tool.

[Funracer]

Originally Posted by AndrewCologne

At 900 rpm swinging around 55% duty cycle at closed loop, means with OX sensor plug connected and therefore lambda regulation active.

This does correspond to approx 0.8 % CO at 50% duty cycle with sensor disconnected, means open loop for doing the test with a CO measuring tool.

From your NineElevenHeaven website:



So duty cycle 55 for factory idle setting but 40-45 to achieve proper mixture for acceleration and WOT?

Sorry Damon88 don’t mean to hijack.

Thanks

[AndrewCologne]

55% at idle is for factory standard (max 0.8% CO).
40-45% at idle ends up in a higher AFR at WOT.:-)

Sorry I was thinking of my own developed ECU, where you always set idle to 55% duty cycle and you can set the AFR for WOT individually via software.

[Funracer]

Originally Posted by AndrewCologne

55% at idle is for factory standard (max 0.8% CO).
40-45% at idle ends up in a higher AFR at WOT.:-)

Sorry I was thinking of my own developed ECU, where you always set idle to 55% duty cycle and you can set the AFR for WOT individually via software.

Got it! Thanks

[Damon88]

Thanks you Andrew for the clarification. Funracer, I appreciate you starting this thread and helping others from what you learned. This is place is amazing. Thanks again. Cheers Damon

[mysocal911]

Originally Posted by Funracer

Got it! Thanks

Read here starting at post #15 to see how some hopefully learned about how a Lambda ECU functions and how it's tested;
High dwell on 911 SC ‘81 lambda (US)

That was over three years ago, and some still don't fully understand the system and still ask questions!