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.

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.

Yes, do tell.

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"

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!!

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.

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.

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.

ohh that 300hp is estimated at the crank..sorry

A lot of power mods are also efficiency mods.... up until you add more fuel....

How much difference do you think those pulleys make. Thats something I've been thinking about for awhile, but I'm skeptical about how much gain you actually get.
My peak boost is at 17.3, but my right foot gives into temptation too easily, so I've been getting 21mpg.

how so?

There's two types of power mods:

• Those that increase power/speed by reducing losses (these are also efficiency mods).
• Those that increase power/speed by making more power out of more fuel (these tend to reduce your fuel economy).

Its hard to say how much of increase i got, i practically did all my mods in the same month. But the stock crank pulley wieghs like 12 pounds. Compared to aftermarket one that wieghs less than 5. (5-8hp) You can get all 3 pulley for under 100$ on ebay right now. Id say thats worth it.

So I have some data to provide. I've filled up my tank but only driven less than a quarter of it so I don't have the trip odometer/gallons at fill up number just yet.
I calculated an average MPG by logging my realtime fuel consumption (in mpg) with my laptop and RomRaider ECU logger. This software reads data from the ECU several times a second and can save it to a spreadsheet file. I added up all of the realtime mpg numbers and divided it by the number of reading the ECU took. The results were surprisingly high, and my highway mile were lower than my city mile so if someone can find a flaw in my methodology please point it out. Here are the results:
46.68 mpg: city driving, light traffic
40.66 mpg: city/highway mix, light traffic
37.73 mpg: highway driving, no traffic

I'll log more tomorrow on my way to and from work and see what those results are.

funny vetts r faster and get better mpg must be the aerodynamic's

boost can increase efficiency by allowing a car to now have to downshift esp if kept at 5-8psi esp on a 1.6 engine which is super efficient to begin with

Boost kills your gas millage. Look at a chart of fuel pressure vs. boost for your car, and see how dramatically it rises with boost.

very true, more boost = more fuel = more power. staying out of boost range works well though;)

it might be a bit too in depth than what you're looking for, but take a look at megasquirt. its a total open source stand alone engine computer. its really made for people that want to play. not overly expensive since you can actually buy a kit and solder it together yourself - theres also pre-built units.

anyhow hook it up to a laptop and you can change *anything* you want to.

the downside is that its a lot of extra screwing around, can have some issues with emissions laws (if they find it i guess lol) and by the looks of things wiring can be an ***.

Going off on a tangent here...

Thank you for reminding me that Megasquirt exists. Does it require a return, or does it operate returnlessly so I could use it as an easy conversion for a carbureted car? I wonder if it would go well on my 1980 Buick...

i think its just for fuel injected vehicles....sorry :(

This megasquirt doesn't do anything I can't already do with my stock ECU, Openport cable, and laptop.
And the changing maps this way can't be detected by ODBii emission checks.

Possibly. More likely it's the reduced drivetrain losses... Drag from all the extra hardware needed for an AWD system can put a noteworthy dent in fuel economy.
If you really want to compare the two, it's worth noting that the most expensive WRX starts at roughly 10 grand cheaper than the least expensive 'vette. 10 grand will buy a lot of gas, and a hatchback with all wheel drive will prove far more practical for day-to-day tasks and dealing with inclement weather than a rear wheel drive sports car.

So just drove off a full tank with this map. Went 296.5 mile on 12.332 gl of gas, for 24.04mpg. The tank was driven off with a good mix of city and freeway driving both with varying amounts of traffic, so it is an improvement over my 21mpg average, still I've seen fuel economy this high on tanks where it was almost all highway driving. For the first half of driving this tank I was taking it easy on the car looking for knock and making sure the map ran OK so the slight increase in mpg could easily be attributed to driving style. Still I'll leave this tune on for now, driving off another tank how I would normally drive and see what figures I get then. Over all this fuel save tune doesn't see to be working well.

I just filled up the wrx the other day and averaged 26.345mpg, with mixed driving

Damn, you beat even my fuel save map. I wish I had more restraint with my right foot. That's the purpose of this map, to try and stay out of the boost, because I can't help but use that power otherwise.

i'm not doubting you here, just curious as one day in the (hopefully) near future i want to build up a turbo 1jz supra...what exactly is an openport cable? can it reprogram any stock computer or just a few manufacturer's?

how do they check for the obd2 emissions regarding the computer? i thought they just took a quick check under the hood and then hooked the thing up to the dyno/emissions computer...

The openport cable is Subaru/Mitsubishi specific, it also works on a few Mazdas. The new v2.0 is compatible with more vehicle but is still by no means universal.

As for emission testing it varies state to state, but generally they do an odbii check where the plug into the odbii port to look for cels and check a few "readiness" parameters

CL AFR is set 14.7 rich 15.5 lean

Does the ECU have a wide band to judge that? If it's relying on a standard 4-wire narrow band sensor, it won't be able to tell the difference between 14.8 and 15.5.

I do not have a wideband 02 sensor, the stock narrowband 02 is fairly accurate but only when around 14-16:1 beyond that it can really only tell if it's rich or lean.
14.7and 15.5 are the AFR targets for CL fueling that I've programed in the ECU, while I don't have a way to accurately monitor AFR without a wideband the ECU will do everything it can to help the engine maintain this range when in closed loop fueling.

No its not a Vette, but my G/F's 3.8l Monte Carlo gets high 20's all the time. she was getting better than my accord. The thing turns like 2000 rpm at 65 mph. My civic does 3200! Big slow moving pistons aren't all bad at FE. Im tellin ya if GM can tweak on their push-rod motor cars, I bet they could build a 30+ mpg full sized car with existing parts. Just maybe they could pull themselves out of this.

So the map seems to be a total fail. Last tank driven off under normal driving conditions was 19.5mpg basically what I'd normally see. Plus my IAM is at 15 and won't get up to 16. Time to rethink this, until then I'm going back to my regular stage 2 tune.