|
Darly,
I think they are referring to the frequency of the feedback cycle at idle, not a delay in switching from open to closed loop. If you watch the needle of a analog dwell meter hooked up the the lambda test port at idle and compare it to cruise, the rhythm of the needle is different. The system trims the mixture at a higher rate at cruise than at idle, which gives a rhythmic beat to the idle. Most programmable EFI ECU's I work with let you change the target AFR for the idle and cruise, and the frequency that the system dithers the mixture, for the same reason. No fuel management system is accurate enough to hold a specific AFR with precision, they have to dither the mixture around a target to make an average AFR. If you want closed loop control at idle, this is how it has to work, and a CIS or EFI engine without an active idle control device will have a fluctuating idle by design.
The Bentley manual has a few errors on CIS lambda and the main sensor testing contradicts Bosch and Probst's books. The 3 mm screw has a much more profound effect at idle than at WOT under load. Few OEM's allow significant user adjustment to the high load WOT mixture for a good reason. The main fuel curve is determined by the FD and the shape of the air funnel. The lambda feedback cycle trims the mixture to keep the cat in a safe range, but has no effect under heavy load. However, the FV must be pulsing in the default range for the fuel curve to be correct. It is curious that no one suggests that removing the O2 sensor in a new Porsche would improve performance, but it does not, for the same reason it does not on a CIS lambda system.
__________________
Paul
|