Rb25 Afc-Neo Afrs/settings - Guru Needed

[2.5T_/<ouki]

Just curious to know what a safe good AFR reading would be while NOT under load just cruising around the city/freeway.

I got my RB25 tuned today (street tune) and would like to know if I'm able to run anymore lean than what it is as I'm going for maximum gas mileage with still being SAFE. Mind you I barely use about 10% throttle when driving anywhere and hardly never step on it.

SETUP: S1 RB25, Greddy IM, FMIC, Boost @ 10psi, Aeromotive FPR, Z32 Fuel filter, 3" From turbo back, walbro fuel pump, HKS bov atmospheric, AFC-neo

My AFR's while cruising are about 14.7-15.2. I was just curious if I could go leaner.

I mainly went so I can get a low throttle tune as I mostly do city driving and barely use like 10-15% throttle all the time. For some reason a 0% low throttle to me looks odd as of we weren't tuning for normal cruising. Most of the time I was just flooring it (WOT).

AGAIN, I went in for a tune STRICTLY for better gas mileage. Someone with SAFC knowledge please chime in.

My settings

LOW THR - 0%

HI THR - 45%

NePoints (HI / LOW)

500 (-2 / +15)

950 (-2 / +15)

1500 (-2 / +15)

2000 (-2 / +5)

2500 (-2 / +2)

3000 (-2 / +0)

3500 (-2 / -2)

4000 (+2 / -2)

4500 (+2 / -2)

5000 (+2 / +0)

5500 (+1 / +0)

6000 (-3 / +0)

6500 (-3 / +0)

7000 (-3 / +0)

7500 (+0 / +0)

8000 (+0 / +0)

Thanks for the help!

[GTSBoy]

You can lean cruise at 15 or 16:1. Basically, if it will run smoothly without any shenanigans, then it is fine. Where this is will vary from engine to engine (both in terms of engine types and specific RB25s), with some able to lean cruise at 17:1.

What you cannot easily do is make an ECU that is running a narrowband oxy sensor run anywhere other than ~14.7:1. On a Nistuned ECU you can switch off the oxy feedback and adjust all of your tune (there's a couple of ways to go about it) to lean the cruise section of the map to wherever it will run acceptably. Most will be able to get up into the high 15s. I guess you can do this on PowerFCs too.

The problem with doing the above is that it is a lot safer to keep closed loop control in the long run. It can help save you from various random problems with fuel pumps or blocked filters or whatever.

Other aftermarket ECUs obviously allow you to do whatever you want. If they're running open loop you just run a lean cruise section. If they're running closed loop, there are tricks available to cruise lean.

Another thing you can do is to use a wideband oxy sensor and get its control box to output a narrowband simulation signal for your ECU. You then bend that simulation so that it's richer than reality, so that the factory ECU will happily run leaner than stoich, thinking that it is on stoich.

Sadly, your AFC is a signal bender for the main load signal (the AFM) and not the oxy sensor. So whilst you can use it to tune your higher load sections, you really can't get it to do anything to the cruise section, because the main ECUs closed loop control will always drive it towards 14.7:1 unless you can use the above trick to confuse it.

[2.5T_/<ouki]

Thanks so much for the reply I truly appreciate it! It makes sense that the stock 02 sensor will always try and get it closest to 14.7. Damn this is a big let down as I mainly went this route to be able to tune partial throttle to run more lean at cruising. I did extensive research but I guess it wasn't enough to fully understand how the factory narrowband would come into play.

I'm truly not sure how to go about tricking the ECU as you said. That seems a bit scary to me. I could have sworn the tuner was able to get my idle around 16 or so but said it wasn't safe so left it at 14.7 give or take.

[2.5T_/<ouki]

Username: AS240 on zilvia.net forums claims he's running stock ECU and safc2 and has his AFRs pulled to 16-16.4 while cruising. I have PMd him to try and see how he is doing this.

http://zilvia.net/f/tech-talk/493277-rb25-whats-your-mpg.html

[paulr33]

you should be able to use the safc load points to the bend the tune on light cruise to get around 15 or 16 on light cruise

i had my powerfc tuned for mid 16s on light cruise and got pretty sweet economy for many years

make sure you are measuring your af/rs using a wideband 02 ssensor and not a guage or reader on the stock narrowband 02 sensor

[GTSBoy]

you should be able to use the safc load points to the bend the tune on light cruise to get around 15 or 16 on light cruise

i had my powerfc tuned for mid 16s on light cruise and got pretty sweet economy for many years

make sure you are measuring your af/rs using a wideband 02 ssensor and not a guage or reader on the stock narrowband 02 sensor

If it's running light enough to be closed loop, you can't push it away from stoich with bent load input. Only bending the oxy sensor signal can do that.

[paulr33]

ah good point, didnt think of that

perhaps disabling the 02 sensor and spending time tuning all the load points via safc may yield better economy?

[_x_FiReStOrM_x_]

Guessing R33 is more advanced with engine management, but on my R32 i can disconnect the o2 sensor and the ecu runs continually in open loop mode, allowing you to set your own cruise ratio via piggyback. It sets a fault code in ecu, but does not illuminate MIL or have any other limp-mode or adverse affects (providing you have a wideband to monitor things). Might be worth a shot, but my guess is the r33 will throw engine light on.

[GTSBoy]

No, same same. R33 ECU is essentially the same as R32 (whilst being completely different). So your method would work, but it's not ideal. I don't love the idea of running the Nissan ECUs open loop. I'd happily run a wideband with bent narrowband simulation to achieve the goal though.

[_x_FiReStOrM_x_]

Ahh yep, learn something new every day . Agreed, its not ideal. The part i don't like about the closed loop, when running with a shitty piggyback setup (standalone is a completely different kettle of fish), is constantly fighting against LTFT. You're either constantly resetting ecu/fuel trims or retuning the map. Not entirely sure about these cars, (but i have found with some others); do these ECU's fuel trimming affect the entire map like reducing a % of total injector, or only the closed loop areas (ie cruise and idle portions)?

Edited January 9, 2013 by _x_FiReStOrM_x_

[GTSBoy]

Yeah, the LTFT is global.

[_x_FiReStOrM_x_]

Ahh thats a bitch. Thanks for clarifying.

[Skyline ja]

I need to kno how to tune the AFC neo RB25de pls help

[wolverine]

Do you have a wideband and any understanding of tuning?