Run lean for better MPG?

[madman]

At this time I'm only using the SFAC and a pocketlogger.

I've use the tuning guide in the tech articles and have everything running great. I've read somewhere that you can tune your lo-throttle lean to get better gas mileage.

Is this an ok practice? How lean can you run it safely?

I don't have a wideband or an EGT so I can use the fuel trims to see how lean or rich I am correct? and if so is > +10 safe to run at low throttle? what's the saftey margin?

 

[GILZTSIAWD]

At low throttle your ecu is going to automatically try to adjust the fuel trims to make it go back to stoich. It will max out at 12.5% though, so if you go past that then I guess you could get it to run lean, but I wouldn't suggest it. If you have a good tune-up and a good o2 sensor you should be getting pretty good mpg anyways, I get about 27.

 

[madman]

Well if a trim at 0 is 100% and a plus number is lean (guide says add fuel), I was running at +11 on the 1k and 2k trims. I noticed this one day when I decided to recheck my tuning. I added fuel and the trim will adjust like you said but they can still stay high/low depending on your settings on the SAFC. Mine where staying high until I changed it.

I adjusted the settings till the trims reached a -1 ~ +1 reading, as good as I good get it. Then I've noticed I lost a little MPG.

So I don't think that the computer will self correct all the way back to zero if are using a SAFC, otherwise what's the point of a fuel controller.

 

[GILZTSIAWD]

It won't go back to 0 because that is how much it is adjusting the fuel. It is showing you how much fuel it is having to add or subtract. The only wait it will get back to 0 is for you to change up the fuel so that it will be just right and it won't have to add or subtract any fuel. The point in the fuel controller is for WOT when your car is in open loop mode. The lo fuel trim is adjustable just so you can dial in new injectors to idle good and drive around good without your car having to add or subtract fuel.

 

[madman]

So is this how you can tell if you are over running (maxing out) your injectors? by how much the computer is working to correct them?

So then it sounds like there is no way to adjust the lo throttle then as I was mentioning.?.?

 

[GILZTSIAWD]

You see if you are maxing out your injectors by the duty cycle on your logger. There is no way to adjust the fuel like you stated for better mpg. You need to just tune it so the lo throttle is 0 and it will run great.

 

[madman]

You see if you are maxing out your injectors by the duty cycle on your logger.

Hmmm.... I havn't played with that option yet.

Thanks.... It's as close to zero as I can get it so I guess I'll leave it alone.

 

[dsm-onster]

Running 14.7:1 (not fooling your ecu into running leaner) is the most efficient a/f ratio for gas milage. Running Stoich insures that the most amought fo gas in the mix is used to develope power. More of the gas in a 14.7:1 mixture will be used to push the piston down than a leaner or richer mixture. For idle/light throttle, if you go leaner, you'll need more throttle (more air). More throttle is more air. More air means more fuel to match it. DSM engineers would not develop closed loop operations and not include the most efficienct a/f muxture for gas milage. You only need a safer, richer mixture when you're invoking load (aggresive driving). And then the ecu goes to the safest "load mixture" that can be run without stumbling: 9.4:1 or smething around there.

 

[MyBlack94GST]

Hah, I've been doing this for years... with 550s I lean out the LOW to -30% for the freeway. Works great... I can drive 50 miles with the gas light on.

 

[madman]

You see if you are maxing out your injectors by the duty cycle on your logger.

My logger doesn't show duty cycle.

 

[madman]

Hah, I've been doing this for years... with 550s I lean out the LOW to -30% for the freeway. Works great... I can drive 50 miles with the gas light on.

What does you fuel trims look like when you're on the highway?




sorry for the double post.

 

[GILZTSIAWD]

Running 50 miles with the gas light only requires 20 mpg. Gas light means 2.5 gallons left. I can go about 75 with the gas light on and my fuel trims close to 0....and I have 1000cc injectors.

 

[dsm-onster]

Hah, I've been doing this for years... with 550s I lean out the LOW to -30% for the freeway. Works great... I can drive 50 miles with the gas light on.

Leaning out to -30% w/ 550s still keeps you in the ecu's fuel control "envelope" and it will pull you back to the stoich a/f ratio (14.7:1) unless your o2 sensor is bad. I got 33 mpg running 80-90 on all three of my fuel trims (650s, FP2X cams, 18g, etc.) and, consequently, running stoich: that translates to over 80 miles with the fuel light on for me.

 

[spyderturbo007]

My logger doesn't show duty cycle.

You can't log or view IDC on a 2g OBD-II logger.

 

[reveal1123]

damnn... i'm getting shitty gas mileage.. 20/25

 

[mavisky]

I have my lower trim maxed out and I logged 22mpg for a tank of hard highway and city driving including an autocross. On normal driving I've pulled almost as much as 30mpg if I can get myself to keep my damn foot out of the throttle .

 

[Reese92tsi]

My logger doesn't show duty cycle.

2G loggers are able to view IPW right? if they are then you can figure out IDC. IDC=PW/time available. To figure out the time it takes to perform a complete engine cycle at a particular RPM a simple formula is used. Time available=RPM/60 inversed by 1 * 2.

ex. PW of 15ms@7500rpm=93.75%DC

7500rpm/60=125rps
1/125rps=.008
.008*2=.016
15ms/16ms=.9375

 

[hose101772]

With the O2's upper swing value at .3 volts, I'm getting 34mpg @70+ on the highway. This has been backed up on another car with the same mod.

 

[spyderturbo007]

2G loggers are able to view IPW right?

I wish.

 

[TurboStutr]

i dont mean to hijack this thread at all, but is it possible to tune for a better a/f for low throttle on a dyno? i had my car on a dynojet a while back with a wideband o2 and i could go from -50 to +50(s-afc I) while cruising in 3rd gear @ 2k rpm and there was no change in the tone of exhaust or a/f ratio. is this normal?

 

[spyderturbo007]

i dont mean to hijack this thread at all, but is it possible to tune for a better a/f for low throttle on a dyno? i had my car on a dynojet a while back with a wideband o2 and i could go from -50 to +50(s-afc I) while cruising in 3rd gear @ 2k rpm and there was no change in the tone of exhaust or a/f ratio. is this normal?

Sounds like you were adjusting the Hi Throttle map on the SAFC-II when you were actually using the Lo Throttle Map.

 

[TurboStutr]

Sounds like you were adjusting the Hi Throttle map on the SAFC-II when you were actually using the Lo Throttle Map.

i dont really understand what you are trying to say...i was definitely making the adjustments to the Low Throttle Map, we later adjusted the Hi Throttle Map and got a good 11.5:1 a/f from 3k rpm to redline. on the Hi Throttle Map, from idle to 3k rpm i just have it set to -15. and i dont know if you just mistyped, but this was done using the SAFC-I, not the new SAFC-II

 

[madman]

i dont mean to hijack this thread at all, but is it possible to tune for a better a/f for low throttle on a dyno? i had my car on a dynojet a while back with a wideband o2 and i could go from -50 to +50(s-afc I) while cruising in 3rd gear @ 2k rpm and there was no change in the tone of exhaust or a/f ratio. is this normal?

No sweat hijacking my thread....I do it when it relates to the same topic.

Read posts 1 - 6, it should help.

Also to sum it up from what I learned, you don't tune Lo-Throttle.....it's for fuel trim/injector/idleing purposes. You are just helping the computer to get to where it want's to be with a good A/F mix. No matter what you set it to it will work it's self back to it's own set ratio.

That's alittle wierd you said you didn't notice any change going to that extreme with the settings though.

In idle if i would adjust the lo-throttle that much I would definitley smell it getting real rich (+) or the oposite...it would try to die on me (-)......I guess with you in 3rd gear and 2k it won't die....but if you let it idle and drop it to -50 I bet it would die on you...

Adjusting it that quick will affect the a/f ratio until the computer catches up.

I have the SAFC I ...It shouldn't make a difference if it's I or II.

 

[TurboStutr]

thanks, i appreciate the feedback....i guess if it aint broke dont fix it.

 

[spyderturbo007]

i dont really understand what you are trying to say...i was definitely making the adjustments to the Low Throttle Map, we later adjusted the Hi Throttle Map and got a good 11.5:1 a/f from 3k rpm to redline. on the Hi Throttle Map, from idle to 3k rpm i just have it set to -15. and i dont know if you just mistyped, but this was done using the SAFC-I, not the new SAFC-II

I thought you might have been cruising around at part throttle (which would put you on the low throttle map) and you were adjusting the high throttle map. Doing that would have produced no change in the fuel curve until you exceeded your TPS trigger point.