Jump to content
SAU Community

Recommended Posts

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!

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.

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.

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

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

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.

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.

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.

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 by _x_FiReStOrM_x_
  • 1 month later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now


  • Similar Content

  • Latest Posts

    • Surely somebody has one in VIC. Have you asked at any shops?  Is this the yearly inspection or did you get a canary?
    • This is where I share pain with you, @Duncan. The move to change so many cooling system pieces to plastic is a killer! Plastic end tanks and a few plastic hose flanges on my car's fail after so little time.  Curious about the need for a bigger rad, is that just for long sessions in the summer or because the car generally needs more cooling?
    • So, that is it! It is a pretty expensive process with the ATF costing 50-100 per 5 litres, and a mechanic will probably charge plenty because they don't want to do it. Still, considering how dirty my fluid was at 120,000klm I think it would be worth doing more like every 80,000 to keep the trans happy, they are very expensive to replace. The job is not that hard if you have the specialist tools so you can save a bit of money and do it yourself!
    • OK, onto filling. So I don't really have any pics, but will describe the process as best I can. The USDM workshop manual also covers it from TM-285 onwards. First, make sure the drain plug (17mm) is snug. Not too tight yet because it is coming off again. Note it does have a copper washer that you could replace or anneal (heat up with a blow torch) to seal nicely. Remove the fill plug, which has an inhex (I think it was 6mm but didn't check). Then, screw in the fill fitting, making sure it has a suitable o-ring (mine came without but I think it is meant to be supplied). It is important that you only screw it in hand tight. I didn't get a good pic of it, but the fill plug leads to a tube about 70mm long inside the transmission. This sets the factory level for fluid in the trans (above the join line for the pan!) and will take about 3l to fill. You then need to connect your fluid pump to the fitting via a hose, and pump in whatever amount of fluid you removed (maybe 3 litres, in my case 7 litres). If you put in more than 3l, it will spill out when you remove the fitting, so do quickly and with a drain pan underneath. Once you have pumped in the required amount of clean ATF, you start the engine and run it for 3 minutes to let the fluid circulate. Don't run it longer and if possible check the fluid temp is under 40oC (Ecutek shows Auto Trans Fluid temp now, or you could use an infrared temp gun on the bottom of the pan). The manual stresses the bit about fluid temperature because it expands when hot an might result in an underfil. So from here, the factory manual says to do the "spill and fill" again, and I did. That is, put an oil pan under the drain plug and undo it with a 17mm spanner, then watch your expensive fluid fall back out again, you should get about 3 litres.  Then, put the drain plug back in, pump 3 litres back in through the fill plug with the fitting and pump, disconnect the fill fitting and replace the fill plug, start the car and run for another 3 minutes (making sure the temp is still under 40oC). The manual then asks for a 3rd "spill and fill" just like above. I also did that and so had put 13l in by now.  This time they want you to keep the engine running and run the transmission through R and D (I hope the wheels are still off the ground!) for a while, and allow the trans temp to get to 40oC, then engine off. Finally, back under the car and undo the fill plug to let the overfill drain out; it will stop running when fluid is at the top of the levelling tube. According to the factory, that is job done! Post that, I reconnected the fill fitting and pumped in an extra 0.5l. AMS says 1.5l overfill is safe, but I started with less to see how it goes, I will add another 1.0 litres later if I'm still not happy with the hot shifts.
    • OK, so regardless of whether you did Step 1 - Spill Step 2 - Trans pan removal Step 3 - TCM removal we are on to the clean and refill. First, have a good look at the oil pan. While you might see dirty oil and some carbony build up (I did), what you don't want to see is any metal particles on the magnets, or sparkles in the oil (thankfully not). Give it all a good clean, particularly the magnets, and put the new gasket on if you have one (or, just cross your fingers) Replacement of the Valve body (if you removed it) is the "reverse of assembly". Thread the electrical socket back up through the trans case, hold the valve body up and put in the bolts you removed, with the correct lengths in the correct locations Torque for the bolts in 8Nm only so I hope you have that torque wrench handy (it feels really loose). Plug the output speed sensor back in and clip the wiring into the 2 clips, replace the spring clip on the TCM socket and plug it back into the car loom. For the pan, the workshop manual states the following order: Again, the torque is 8Nm only.
×
×
  • Create New...