b5m

Just when I thought I had it all figured out:

When does the ECU run in open loop and closed loop? And when does the O2 sensor come into play?

My understanding is that in closed loop(feedback mode) it is using the O2 to check the mixture and adjust to a target. Why does it not always use this mode since the O2 sensor gives readings throughout the range?

john banks

The O2 sensor is unreliable when too hot and reads overlean, it is also really designed for only one thing - to tell you when you are at stoichiometric mix for the cats/emisssions at closed loop. Open loop needs to be richer for cooling.

b5m

So when does it switch from closed loop to open loop? Is it revs/throttle or some combination?

mutant_matt

I think it switches when either:

a) You use a certain amount of throttle (at any revs). Not sure how much throttle but Full throttle is certainly one....

b) You go into Positive Boost (but this may actually be when you hit 0.5bar)

c) You go above 3800rpm

Hopefully, someone else will provide the exact figures for you but here is a rough guide.

Matt

john banks

Watch delta dash and observe - air fuel correction is zero.

Cosie Convert

Agree with Matt on A and B. I think C can vary by MY. My Ra with it's ultra low gearing can sit at 4500 cruising on light throttle in top gear and still be closed loop. Apply slight throttle and it instantly goes open loop.

spence7

I heard it ran closed loop i.e. with lambda sensor in the loop if the following conditions were met:

1-there is positive or zero vacuum in the exhaust manifold i.e. foot off the pedal or coasting. So under any acceleration other than downhill it'll run open loop

2-revs were below 4700rpm. I think this was for UK scoob though not sure.

who knows, I guess the ECU's settings would change depending on the model year as well like?

mutant_matt

John,

I may run some DeltaDash tracing tonight as I've got no data which I can refer to which would help prove this point.

Spence, sorry to pull your post appart but it's very confusing:

"I heard it ran closed loop i.e. with lambda sensor in the loop if the following conditions were met:

1-there is positive or zero vacuum in the exhaust manifold"

Other way round, that is Open Loop.

"i.e. foot off the pedal or coasting."

That is Closed Loop

"So under any acceleration other than downhill it'll run open loop"

Only if you are on zero or positive boost (exact figure being debated) and then your foot will be ON the pedal (creating boost). Depending how much on the pedal will determine Open/Closed loop.

Matt

spence7

No no, I always appreciate a bit of healthly criticism !

To be honest though, even though I'm sure you'll constructively correct me, I think I'm right. In the sense that positive *vacuum* (rather than pressure) / zero vacuum equates to no throttle/coasting (no acceleration) respectively. Am I wrong here? So ecomony is required hence closed loop no?

Yeh agree with last bit, coasting / no accel is still partially open throttle....which will give closed loop operation, open loop is a floored pedal situation (% flooredness tbd as you say)

Never thought it was related directly to boost though I have to say, just manifold pressures (or lack of) and rpm. Dunno!

cheers
Alex

mutant_matt

Terminology mixup then Well of course you would think that...OK, so positive vacuum means negative pressure/true vacuum - so we were agreeing with each other BTW, no throttle at all means more negative pressure/positive vacuum ( ) than say at idle.Yes. For economy and to be Cat friendly, stoich is required which is achieved via the closed loop control.

Good, we are all in agreement

Matt

john banks

Ladies, I can't be ar$ed reading it all and making it a threesome Just look on Delta Dash and all will be revealed

mutant_matt

John,



Matt

P.S. I will look on DD when I get a chance to do a run which tests this one....