SAFC tuning... a possible cheat?

[H@xtGSX]

I basically have a question about ECU response. I know that tuning with the SAFC while the ECU is in closed loop is basically pointless, as the ECU will eventually compensate for what ever the SAFC settings are. When you mash the throttle to the floor though, it is flipped into open loop, where the SAFC can do some good. Most people tune to this via flooring it and seeing where the AFR goes or what a loggers says at WOT... But is this necessary? What if you were to just disconnect the O2 sensor, thus forcing the computer into open loop all the time, so you could tune to all the conditions between idle and WOT without having to set land speed records on roads you're likely to get a ticket tuning the other way? Is this a viable solution to getting an SAFC tuned for a more complete set of conditions?

 

[Chicken Patty]

Well since the AFC has LO and HI throttle settings, you can still do something to closed loop. When I ran an S-AFC, I used EVO SCAN to log and whereever my closed loop fuel trims needed some adjustments, I would just dial it in with the AFC and so forth. No need to disconnect the sensor.

 

[H@xtGSX]

I understand that it will affect the closed loops settings, but when you are tuning for the hi settings, you aren't tuning a closed loop condition. I have mine pretty well set with closed loop fuel trims staying close to where they should be, but getting it set correctly for the best top end response has been tougher. I have a couple points the fuel isn't right and causes some rough backfiring or popping as the rpms rise and I haven't been able to tune them out without just making the motor bog down on way too much fuel. If it were in open loop continuously, I think it could see exactly where that condition occurs with my WB better. Right now I don't have a logger, but I am ordering a cable and getting EVOScan in a few days.

 

[jcart953]

Why dont you just take it to a dyno and pay like what 60-70 for 3 pulls and tune WOT that way so you can solve your problem easier without worrying about those tickets?

 

[H@xtGSX]

Why dont you just take it to a dyno and pay like what 60-70 for 3 pulls and tune WOT that way so you can solve your problem easier without worrying about those tickets?

If I had that option I would've already done it. The nearest dyno to here is literally 175 miles away, and it is 2WD... I don't have that kind of time very often, and when I do it is normally already allocated to wife and daughter stuff. I have to do it myself.

 

[steve]

Disabling the O2 sensor will cause the ECU to run in one of it's limp modes. Can't really tune then.

What sort of "tuning" are you trying to do?

The first step is creating compensation adjustments for the changes you've made. I don't consider this tuning.

Your trying to get the ECU back to behaving like it would stock in closed loop after changing the injectors or messing with the fuel pressure. Once your closed loop fuel trims are back to normal you can start move those corrections over to the open loop settings as a baseline and start tuning.

You want the closed loop settings right so that when the ECU switches to open loop there isn't a big jump due to the difference between expected and actual AFR from the lack of feedback.

With the SAFC the closed loop corrections are in the low settings and the open loop tuning done in the hight. You set up the switch over point between high and low based on where the ECU switches from closed to open relative to TPS voltage and where you want your tuning to apply. The SAFC interpolates between the low and high settings if there is a middle ground in the TPS range for switching.

You might not want as aggressive corrections from stock fuel maps in case where you didn't mash the throttle open.

So, tuning with the SAFC while the ECU is in closed loop is not basically pointless. You just need to understand what the point is. While your in closed loop the AFR is targeted to an average of 14.7:1 based on the feedback from the O2 sensor and the fuel trims work to maintain that AFR. The point is to make corrections with the SAFC to bring the fuel trims as close to possible to 0 so that when you ask the ECU to go open loop the actual AFR will be close to the target AFR in the maps. and your Tuning then is where you want to deviate from the factory AFR.

Just remember that the SAFC can't change the map directly, it lies to the ECU about airflow and airflow is a primary factor in how the ECU decides how much fuel and timing to use. Big SAFC corrections tend to also add big timing changes which might not be what you want or expecting.

 

[Chicken Patty]

What I used to do is set the throttle points at 35%-50%. That worked best for me. Just tune your LO settings to where your fuel trims are good, and then tweak your HI to where your air air/fuel ratio is as desired.

Steve's post above is all you need to know.

 

[steve]

Steve's post above is all you need to know.

Not even close to all but it's a place to start from.

 

[H@xtGSX]

Thanks Steve and Chicken Patty (it feels weird saying "thanks chicken patty" ). I tuned to 0 fuel trim closed loop, at normal driving conditions... Really, at normal conditions, I'd prefer it to run a tad lean and save me a buck or three, and I tried to incorporate that by turning the settings down until they started pegging lean and then backing off a bit. What that gained me was a real rough timing pull at 4k. I backed off a LOT there, and 500 each side, and now it just bogs. There doesn't seem to be a happy middle ground. If I floor it, open loop will hang around 11.5:1, and right at 4k bog down to 9:1 and spit fire out the pipe. I have the same issue if I lighten up the settings, same spot. Plugs are gapped and I'm running COP's. I tested the coils also, and their output is identical across all 4, nice and hot. Hi/Low is set at 35% and 60%.

Basically, I'm stumped, and I have started building a water injection system, putting a 3 bar MAP in to take over the throttle position sensor's job to make the SAFC boost referenced instead, and fabricating a cold air intake. I installed the MAP sensor today, and it helps. The response is quicker, bit it hasn't fixed the 4k fire farts... And they are melting the rear bumper. I have messed around with it so much, I have burnt at least a couple full tanks trying to figure the damn thing out. I don't usually ask for help, as I like to figure this stuff out on my own, but this is seriously driving me nuts.

The only other thing I can think of is if the AFPR is being a dumbass right there, but I don't have an in cabin fuel pressure gauge... I need to get one though. I pulled the 550's, and they don't appear to be damaged or leaking, but I am running a Whinebro 255 HP. I have a beefy AFPR custom made by OER in Japan, and I highly doubt it would be the culprit... It is capable of handling dual 255's without a hitch............but I can't think of anything else it might be.

 

[Chicken Patty]

You are runnjing 550's and pulling 35% on HI and 60% on LO? I thought you could only pull 50%?

Anyhow, you shouldn't have to pull 35% on your HI map. I ran 750's and I didn't have to pull so much with the S-AFC. What's your base fuel pressure set at?

 

[H@xtGSX]

You are runnjing 550's and pulling 35% on HI and 60% on LO? I thought you could only pull 50%?

Anyhow, you shouldn't have to pull 35% on your HI map. I ran 750's and I didn't have to pull so much with the S-AFC. What's your base fuel pressure set at?

No, those are my throttle points. What I am pulling to compensate for the 550's isn't going to sound right to you unless you've used the pot mod to keep from getting the 0300 random misfire CEL. I actually have to add a significant amount at lower rpms. I just tune to the wideband and the fuel trims. I have changed things as of 20 minutes ago though... I took the throttle position sensor wire off and attached it to a 20-250 KPa MAP sensor instead. It makes more sense to have the correction based on engine load than some arbitrary throttle point. I am basically having to start over with my tune, but I am hopeful this will improve the SAFC correction. I have driven it a little and I can already tell it is much more responsive. No hesitation when you step on it... I'll get it within a decent tune by tomorrow and see if the problem still persists.

 

[H@xtGSX]

Well, I am happy to report that boost referencing the SAFC made a HUGE difference. The car just drives better. The engine responds faster, I gained several MPG on my 45 mile work commutes, the turbo spools quicker, and I was able to set my correction settings where they should be and still keep the fuel trims in check. The 4k fire farts are gone too. It now pulls very consistantly all the way to 7k. I can't believe more people don't boost reference their SAFC, because now, instead of having a sweet spot where the throttle position is roughly matching the engine load, the correction is correct over the entire spectrum of engine loads. It's a major improvement and allows the SAFC to control things in a much more logical manner for a boosted engine. Once I got the settings close, the car basically tuned itself. I will start another thread to discuss this though. Basically, my initial question about making the ECU stay in open loop to ease tuning is a "NO", so I am marking this resolved.

 

[Chicken Patty]

Thanks for the input man!

 

[H@xtGSX]

No, thank you!

Take a look at the other thread I made for boost referencing the SAFC. It is a seriously worth while upgrade. I am really impressed with how much more efficient it is.