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Old 08-11-2009, 02:05 AM   #1
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Fuel Saving Engine Map

Hi everyone. I'm fairly new to this forum but thought I'd share this.
I have a Subaru WRX with a 2.0L turbocharged motor. I've recently been learning about open source tuning, and bought an OBDii to USB cable and a small netbook to keep in my glove box.
As we all know turbo charged cars to start with tend not to be fuel efficient (unless you can stay out of boost) and I've done a few mods to my car and all of them have been for gains in power and performance, knowing full well that would come at the expense of MPGs (3" catless turboback exhaust, catless uppipe, some light port and polish, and a stage 2 tune (and custom headers and ported intake manifold on the way)). But I've realized while that performance is losts of fun to have on the weekends, its not being used during my daily commutes.
So the first custom tune I made for my car was a fuel save map for when I'm just driving to and from work or when I can expect to be stuck in traffic. Since I have a computer in the glove box it only takes a minute to change engine maps and flash a different one onto the ECU.

Here is what I did. I zeroed the entire wastegate duty cycle table, this make it so that the wastegate is always open and the maximum boost you produce will be the wastegate spring pressure, on my car thats about 9psi (as opposed to 17psi of boost with my stage 2 map).
I changed the Closed Loop/Open Loop Fueing Delay back to their stock values, this ensures I stay in CL fueling longer, and set the CL AFR target to 14.7 (rich) and 15.5 (lean).

I just put this map on today, and initial results look promising. Under daily driver conditions, the car seemed to drive almost exactly the same. There was a slight hesitation in the throttle, but I never found myself lacking any power. I drove around town doing a few errands, and then went to a friends house a few miles away. I was driving both highways and surface streets. Based on the fuel gauge (which we all know are not that accurate) I'd say it dropped almost 50% less than what it would normally. Now I'm willing to concede that these gains may be mostly from driving style as I was driving easier on the car until I see how the car drives with this map.
I had a little more than 1/4 tank when I flashed this map on, so it will be interesting to see the results when I drive off a full tank on this map I've been logging my millage for a few months now so I've got something to compare it to (between 17mpg and 21mpg before the new map).

So far the car drives fine with this fuel save map and since I haven't detected any knocking yet, in future I may advance the timing and lean out further.
I'll keep posting further results.
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Old 08-11-2009, 04:23 AM   #2
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Which OBDII->USB cable did you buy?

What software are you using?

I'm very interested in open source tuning but I don't think any such software is available for any of my vehicles.
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Old 08-11-2009, 04:52 AM   #3
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Yes, do tell.
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Old 08-11-2009, 12:43 PM   #4
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idle, light cruise, cruise 15.5 to 16.5 = best economy!!!!!

I just put 1.7 gallons in my tank and I've driven like 63 miles and I still above the "E line"
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Old 08-11-2009, 03:02 PM   #5
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I am able to get 26mpg with mix driving with those exact same mods on my Subie. I get 30mpg straight highway at 63mph. For a car that has close to 300hp that ROCKS!!
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Old 08-11-2009, 07:11 PM   #6
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Quote:
Originally Posted by theholycow View Post
Which OBDII->USB cable did you buy?

What software are you using?

I'm very interested in open source tuning but I don't think any such software is available for any of my vehicles.
The cable I used is the Tactrix OpenPort cable v1.3 it's specific for subarus mitsubishis and some mazdas.
The software are both free opensource programs called RomRaider and ECUFlash.
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Old 08-11-2009, 07:16 PM   #7
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Originally Posted by vxdude View Post
I am able to get 26mpg with mix driving with those exact same mods on my Subie. I get 30mpg straight highway at 63mph. For a car that has close to 300hp that ROCKS!!
Wow, 30mpg! I've gotten as high as 25mpg on mostly highway driving, never got anywhere near 30. I usually average 21.
What year is your subie, is it a wrx or an sti? If you're at 300whp with just those mods I'm assuming you've either got an STi, or a Rex with a fairly aggressive tune.
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Old 08-12-2009, 07:34 AM   #8
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Its a 2003 wrx, i got underdrive pulleys, turbo back exhaust, perrin Y-pipe, Ported throttle body, k&n airfilter, gutted up-pipe. Stage 2 ecu from Cobb. My boost is at 16.5. The thing of it is i rarely ever go above 3000rpm.
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Old 08-12-2009, 07:37 AM   #9
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ohh that 300hp is estimated at the crank..sorry
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Old 08-12-2009, 07:39 AM   #10
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A lot of power mods are also efficiency mods.... up until you add more fuel....
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I remember The RoadWarrior..To understand who he was, you have to go back to another time..the world was powered by the black fuel & the desert sprouted great cities..Gone now, swept away..two mighty warrior tribes went to war & touched off a blaze which engulfed them all. Without fuel, they were nothing..thundering machines sputtered & stopped..Only those mobile enough to scavenge, brutal enough to pillage would survive. The gangs took over the highways, ready to wage war for a tank of juice
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