Closed loop lambda control

[JCMarshall_Law]

Does anyone know when the ECU in skylines (specifically RB25DET) run in Closed loop lambda control mode, ie; adjusting the air fuel ratios based on O2 sensor readings. I have heard it only runs closed loof on cruise (after sufficient time at constant RPM), but I have also heard they run closed most of the time, only going into open loop on full throtle.

Thanks in advance.

[RB30-POWER]

The tuning on the factory ecu has the car in closed loop with anything below atmospheric pressure in the manifold.

i.e, it doesnt go out of closed loop and into open loop until you hit 0 vacuum or any positive pressure above that.

The only reason it would not be in closed loop under those conditions is if the sensor was stuffed or the engine had just been started. (It takes a few minuted for the O2 sensor to warm up)

They are pretty good, the design of the combustion chamber with good squish zones allow them to run closed loop/stoich ratios even under low manifold pressure. Alot of older cars will go into open loop when the manifold is still under vacuum.

I hope that all makes sense.

[JCMarshall_Law]

Hey, thanks a lot for that Mr Power. Makes sense to me.

[Cubes]

Taking note of the PFC I find the O2 sensor is in closed loop under light acceleration and cruise. It reacts very quickly, if you are within a closed loop enabled load point then you will be in closed loop.

The o2 sensor is disabled when you hit certian load points, nothing to do with manifold pressure/vac.

[RB30-POWER]

You should make those load points closed loop enabled as well.

If the factory ecu can run with stoich mixtures anything under 0 manifold vacuum the powerfc should as well.

Or alternatively, disable closed loop altogether and tune light load to leaner then stoich to pick up even more economy where possible.

[Cubes]

I find on the PFC with the rb30det positive manifold pressure is over load points 15.

Might have to get that checked out. The slightest flick of the accelerator has load points dipping straight to 15.

[benl1981]

So if you have a fuel adjuster such as SAFC etc does it gain by leaning it out under closed loop or does it just keep adjusting to get it back to AFR of 14.7

[RB30-POWER]

SAFC is usually only used to lean out the open loop high load/boost areas. This is where you make your power gains, especially with the Nissan ECU's that run way rich under load.

If you change the AFM voltage in closed loop with the SAFC, the ecu will re-adjust the mixtures to 14.7:1. However the timing would have still changed because you changed the AFM voltage to the ecu with the SAFC.

[benl1981]

I'm suprised they stay in closed loop that much. I'm getting about 12-13L/100km from a manual R33, maybe I should change the 02 sensor out of routined maintenance.

If it is running 14.7 most of the time I would think fuel consumption wouldn't be that bad. I guess it's got a lot to do with how often you put uyour foot into it also.

[GTaaargh]

I had my car run up on the dyno to check whether the O2 sensors were working on my GTR. I was interested in knowing when it was in closed loop, as that's where the best fuel economy should be.

Apparently the standard R32 GTR is in closed loop until around 3000 rpm if it is under light load (< 30% ?). Mine stays in closed loop until 4200 even under full load. His guess was that at 4200 rpm, my 80mm AFMs were putting out the same voltage as the standard AFMs did at around 3000 rpm.

The result is that I'm still in closed loop when I'm on 4 lb boost.

Does his suggestion sound reasonable?

[Cubes]

Apparently its optimal to have the car run in closed loop up until around 30rwkw.

I think the PFC uses the fuel map to determine when to bump out of closed loop mode. Once the fuel map value goes over 1.047 or something. It may also have a little to do with the throttle position sensor.

I really have no idea, possibly its a little of both.