Tuning for Fuel Economy

Traveled about 800 miles yesterday and had a chance to play with the tune. While I was expecting and hoping for cold weather for testing the below 60*F MPG drop, weather turned for the worse with snow and traffic. Both of those really mess up the MPG averages and make it hard to do consistent drives.

Quick Glossary:

IAT = Intake Air Temperature

TMIC = Top Mount Intercooler

AVCS = Active valve control system

Intake & TMIC Blocking to increase IAT

I wanted to first try to get higher IAT's reducing the efficiency of the airbox and by blocking the intercooler. If your going to make the intake less efficient you need to also make the intercooler be less efficient. Sadly the IAT sensor is part of the maf before the turbo or intercooler, so it's readings can be way different from actual post intercooler temps. This is why I had to block both to increase temps.

Removed stock ram air plastic, and setup a cardboard block, which should stop fresh air from front form going into the airbox.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Intake/General/20141125_191745.jpg~original

Blocked the intercooler, this increased the intercooler temps to be about 20*F warmer.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Intake/General/20141125_185357.jpg~original

Stock scoop does have holes for sending cold air to the turbo, which I didn't block.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/Engine/Intake/General/20141125_185429.jpg~original

Data

Ambient Temp: 37*F

IAT's: ~50*F

TMIC Temps w/Block: ~60*F

TMIC Temps w/o Block: ~40*F

Conditions: Wet/rain, no snow

Road: I64 West VA, but after the mountain peaks

AVCS: 10*

Timing: ~46* @ 70mph

MPG: 24.39

Conclusion: the cardboard blocks didn't help, they might have actually hurt the fuel economy.

Fool the ECU to think it's 70*F IAT

I completely forgot that I could just fool the ECU into thinking it was warmer weather by messing with the sensor scaling. This would help me see if an IAT based compensation table at fault for lost fuel economy. For this I returned the intake system to stock (with ram air plastic) and removed all of the cardboard.

Stock vs Modified IAT Scale

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/IAT%20Comp/05LGTIATSensorScale.png~originalhttp://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/IAT%20Comp/IATScaling70F.png~original

Data

Ambient Temp: ~40*F

IAT's: ~45*F

TMIC Temps w/o Block: ~40*F

Conditions: Dry & Sunny

Road: I64 Kentucky

AVCS 10*

Timing: ~45* @ 70mph

MPG: 28.28

Conclusion: I think that actually worked! Which means the cold weather MPG drop is probably mostly ECU related. Car didn't feel like it was racing, it was driving similar to 60+ weather.

AVCS 20*

With this test I returned the IAT scale to stock and wanted to see if more intake AVCS would help. I went extreme with 20*, which with stock downpipe had yielded me some of the better economy.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS20v3.png~original

Data

Ambient Temp: ~40*F

IAT's: ~45*F

TMIC Temps w/o Block: ~40*F

Conditions: Dry & Sunny

Road: I64 Indiana

AVCS 20*

Timing: ~46* @ 70mph

MPG: 26.78

Conclusion: While this definitely was better economy then the first fillup, it was still falling into the same under 27mpg below 60*F trend. Perhaps less AVCS (15*), would help, but I doubt it because learning views at 20* were clean.

Zeroing IAT Compensations

Since messing with IAT's helped more then more AVCS, next run I decided to see if I could zero out the compensations and see if economy improves. Four tables that use IAT based compensations are Wastegate Duty Comp A&B, Timing Comp, MAF Comp.

Stock IAT based compensations:

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/IAT%20Comp/05LGTStockIATComps.png~original

Zeroed them out for the temperature ranges that I was in.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/IAT%20Comp/IATCompsZeroed.png~original

Data

Ambient Temp: 42*F to 33*F

IAT's: 47*F to 35*F

Conditions: Cloudy & Snowing for 1/2 miles, traffic

Road: I64 Illinois

AVCS 10*

Timing: ~46* to 47* @ 70mph

MPG: 25.29

Conclusion: First 60 miles were dry smooth sailing, next 80 miles were not so good. First it started heavily snowing, but roads were not bad. Then I hit 1hr of 1mph traffic, that go me about 20 city miles which at 17 mpg really kills your averages. Thus I was impressed to see even 25mpg. Thus I'm now sure it's one of the 3 compensation tables that are at fault. Car also didn't feel like it was racing, like before.

Update: Zeroing the IAT comp tables didn't seem to help, got 26.91mpg at best on a more consistent highway trip. Thus it's either another table or another non tune variable.

Overview of the 4 Compensation Tables

Timing Compensation (IAT):

This table adds 1.05* at 50f and 2.11* at 32f. I personally don't think it's this table at fault, because stock timing is 40* and I saw this MPG drop with running 41* timing before. In this case I'm running 45-47* of timing.

Initial/Max Wastegate Duty Compensation (IAT) A & B:

These tables start to remove -4.7 duty cycles at 50*F. Which means between 50*F and 68*F they will be interpolating and removing less duty cycles and hitting 0 by 68*F.

I think it could be this table at fault, by removing initial and max duty cycles, the car might have to work harder to keep it going the same speed, which means more throttle has to be used. The thing that trumps this theory though, my Initial and Max duty cycle tables beings at 0 until 24% throttle. Logs show that I'm at 14-18% throttle at 70mph.

MAF Compensation (IAT):

This table didn't really catch my eye for a while because I wasn't reading it right and logging Mass Airflow. On one of my highway logs my average Mass Airflow was 30 g/s. Which means that at 32*F ECU would be pulling about 1% of fuel. That means at 50*F in theory the ECU will be pulling 0.5% of total fuel.

This plus colder denser air could be causing the engine to lean out, which means powerloss thus needing more throttle for same speed. But the O2 sensor should be correcting for this and keeping AFR's at 14.7.

I'm open to comments and suggestions, I will be driving back another 800 miles next week and will be trying to find the culprit table .

Rear O2 Compensations Zeroing

Most people see a pretty bad MPG drop when they would go to a catless downpipe (or catted but rear O2 is before the cat like in factory configuration). This is because 32bit Subaru's also use the Rear O2 sensor feedback to adjust the fuel trims. Without a cat infront of the Rear O2 sensor the readings will be leaner (O2 sensors read oxygen content, catalytic converts burn up oxygen along with fuel), which will make the ecu constantly add additional fuel.

On my 04 Forester XT with 160k miles, with stock downpipe but catless up pipe I gained around 2MPG in the city from this change! This could be because I have 1 less cat then what the car was meant for, or because of exhaust leaks, or because of a worn out rear O2 sensor. Either way I was pleasantly surprised to hit 20mpg city, when before I would get 17-18.

Rear O2 Compensations consist of two tables, AF 3 Learning Limits and AF 3 Correction Limits. The factory tune allows the AFR to be swayed from -0.5 to 0.5 lambda, in AFR speak it can sway the tune by 7.35AFR in any direction! This can be seen in the top images below. The second set of images shows those tables being zeroed out so that ECU can't adjust the fuel mixture based on the Rear O2 sensor anymore.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/Rear%20O2/AF3CompsZeroing.png~original

Sadly these tables are not defined in RomRaider or EcuFlash by default, your gonna have to find the table hex numbers and create new tables in EcuFlash. Refer to these two threads to find the proper values for your ECU.

AF#3 (Rear O2 sensor) correction limits

Rear O2 sensor closed loop fueling target limits

For O5 LGT A2WC522N Use:

AF3 Correction Limits - 2DF2C

AF3 Learning Limits - 2C91C

For 04 FXT A2ZJ5I2I Use:

AF3 Correction Limits - 293C4 (Stock Correction limits will be in percent; High: 50.00%, Low: -50.00%)

AF3 Correction Adder - 5D558 (Stock Adder limits will be High: 0.000500, Low: 0.000350

Bad news, zeroing out the compensation tables didn't pass the test of time. During the trip I noticed that MPG would drop and night but increase during the day. Only two reasons come to mind, tire pressures get warmer during the day due to sun shining on them and other reason is daytime air, even though it's same temp being less dense then night time air.

Tire pressures is what holds the most merit in my mind though. On the trip back I started out with 34psi front and 33 psi rear (didn't have air pump handy), and after 2 hours of driving they only warmed up to 37.5psi front and 35.5psi rear. Even with the temperature compensations being zeroed I still got 25.80mpg at best. Once I filled up the tires, the MPG did increase, but it's hard to say if it was the tire pressure only doing the work.

Since driving in one direction terrain inconsistencies will increase or reduce the gas mileage. For this reason when I drove to the neighboring city that I usually go to for this kind of testing. Last time I drove there it was 25-30F ambient and I got 26.10mpg. This time with IAT comps zeroed for the 3 tables, and 5* timing less at 70mph (stock 40* instead of 45*), with 35-44F ambient temps I got 26.91mpg which is within margin of error in my opinion. Reason I ran the stock timing is because it got me the better gas mileage while on the return trip. It could still be the tune, just not one of the 3 tables that I zeroed. Forcing the IAT to 70*F and seeing if I get improvements going to this city will tell me for sure.

I'm back to the drawing board on what causes the car to loose 3-4mpg as soon as temps hit below 60*F. I'm really starting to think it's tire pressures. I'm hoping to go on another drive this weekend with same tune as above and just higher cold tire pressures. Above two tests I used 36psi front and 34psi rear cold. Which after 130 miles is 39.5psi front and 38psi rear.

I've been wanting to test the tire pressures more to rule them out as the reason to why mpg drops. Filled the tires cold to 42/40psi front/rear and went to the same city as the last couple times. Warm the tire pressure was at 45/43.5 front/rear. Temps were consistent at 37F on the whole drive which is similar temps as before. Increased tire pressure got me 28.72mpg at the pump! Subaru's seem to be very picky on tire pressures, worst then any other car I've ever owned.

Here is my current theory on why below 60*F temps drops the gas mileage. 1.Tires, 2.Denser air = more aerodynamic drag 3.Colder fluids = more mechanical drag.

Tires heat up and air expands as you drive up to a certain point. With colder ambient temps, tires don't get nowhere near as warm as they would on warm day. So far the car seems to like about 45psi warm and starts getting better gas mileage. This makes sense since AWD means more drivetrain loss, thus reducing the rolling resistance as much as possible helps more then on a more efficient drivetrain setup.

I've been measuring tire pressures right as I stop before they start cooling down and writing them down for reference, sadly I only started doing this after it stopped being warm, thus will have to grab warm numbers before summer gas goes back in and adds another variable.

Cold 36/34psi, warm 39.5/38psi at 35F.

Cold 42/40psi, warm 45/43.5psi at 37F.

I believe 36/34psi cold tires would be closer to 43/41psi on a 60*F day. Another interesting variable, front tires tend to raise less then the rear tires on a cold day. I believe this is because front tires are exposed to more cold air then the rear tires which have air deflectors and front tires as air deflectors too.

Sorry, too much reading, didn't go back, but have you considered generally that:

1) Colder weather means your car takes longer to warm up even while driving and therefore while the engine is colder it's much less efficient

2) Idle speed is higher and for a longer period of time so those stop signs and lights and the seconds before you pull out of your driveway add up to a lot of gas

No worries, this thread is more for searching as people run into this. Discussion is always welcome.

1. Correct, and this will affect city driving the most. For highway trips I will warm up the car at the house, then go get gas at Shell and go straight on the highway. This avoids cold engine/transmission inefficiencies.

2. Since this is mostly highway driving, there is minimal city driving 2miles tops usually. By the time I get to the city part, the car is fully warmed and high idle is not a factor.

Warming up in your driveway isn't the same as warming up while driving. Don't forget about things like your transmission, wheel bearings, etc.. Thicker fluid = higher resistance.

I know, but this is why consistency is the key. I definitely got better gas mileage when I was going across country because the car was fully warmed up between fillups, but the roads were not as consistent (elevation wise) as doing A-B-A trips, thus those numbers can't be compared against anything.

Here is my testing process..

1. Check Weather to be in similar range as previous test
   
2. Check oil, fill up tires to desired level
   
3. Flash New Tune, if not testing tune then reset ECU.
   
4. Warm up car for couple minutes
   
5. Drive 2 miles to gas station
   
6. Fill up with Shell 93 gas on lowest speed
   
7. After first punch out, count to 10 seconds, enable lowest speed again and let it punch out again
   
8. Drive 65 miles (elevation 1300-600), stop to get food (delicious burger joint that I like)
   
9. Drive 65 miles back (elevation 600-1300)
   
10. Get to same gas station/pump, check tire pressures, fill up same way as above
    

I found that I get much more accurate and consistent numbers filling up at at least the first quarter tank mark. If I fill up before the first quarter tank the results usually are too optimistic. Like say filling up at 80 miles will get me higher MPG then filling up at 120 miles. I believe this is due to gas pump inconsistencies. But if the car is thirsty that day, I'll barely get to 80 miles on first quarter. The key is driving enough to get you to fill up at least 4 gallons of fuel.

Thus warmup variable is not as big of a deal as long as you are doing apples to apples comparision. Now we all know that during warmer weather the car will be more efficient, I'm not trying to get my winter MPG closer to summer one, I'm just trying to improve the car efficiency overall. By making the car get almost 29mpg while it's cold, means the car should be getting over 30mpg when it's warm .

More testing, this is to another city 2hours round trip. This one involves going over a 2,00ft mountain, thus adds another dynamic for MPG testing. While going through West VA, I got abysmal MPG's, and I wanted to see if closed loop to open loop delay being disabled was to blame.

Usually going to this city I would get 26-27mpg with temps below 60F with tire pressures at 36psi front and 34psi rear.

City A

Tune: Closed Loop to open loop delay on, 3 IAT comp tables zeroed out

Timing: 40* stock timing +0* IAT comp

Ambient: 48-55F

Cold Tire PSI: 42f/40r @46f

Warm Tire PSI: 48f/45.5r @55f after 60m

Dash Gauge MPG: 27

Pump MPG: 28.40mpg @ 70mph

City B

Tune change: Closed Loop to open loop delay off, Stock IAT comp tables

Timing: 40* Stock timing +2* from IAT comp table

Ambient: 38-48F

Cold Tire PSI: 42f/40r @43f

Warm Tire PSI: 47f/45.5r @48f after 60m

Dash Gauge MPG: 26.4

Pump MPG: 29.23mpg @ 70mph

29.23mpg is my personal best winter round trip mpg so far and it's my best MPG ever to this specific city, even my summer MPG to this city was 28.05mpg at best.

Thoughts about CL to OL Delay:

I don't think the open loop delay being on (OEM tune has it on) helped at all. I always here WRX guys saying that disabling the closed loop to open loop delay would cost them mpg's, but in my personal logs with non aggressive driving I see no difference or an actual improvement.

While going straight up the mountain at 70mph, my boost gauge would sit at 0psi a lot, but it would rarely get into boost, but since this is only a 2,000ft mountain. West VA ones go up to 3,500ft easily, thus I do remember those getting into more boost, which is where CL to OL Delay would cut back the amount of fuel used.

Another thought on why disabling the delay actually helps, less fuel means less torque, less torque means more throttle for a longer period of time. By having the delay be always off, you run a little richer but you make more torque thus you use extra throttle for a shorter period of time.

IAT Comp Tables:

I hate to introduce multiple variables, but due to cost of gas and cost of time, sometimes have to test changes in bulk and then dissect them to see what helped or didn't help.

Since this is a round trip run, any mpg gained from downhill terrain you loose when you go back uphill. When I was testing the IAT comp tables initially, it was all one direction, thus I must have hit a nice downhill patch through one of the states that made it seem like IAT comp tables were at fault.

Thus I can comfortably say that IAT comp tables were not to blame for the winter MPG downspike, I'm pointing my finger to tire pressures as the culprit.

Tire Pressures

There are plenty of magazines that tested tire pressures and said on their xyz skinny tire cars increasing tire pressure made no difference. I do believe that my tire size (225/45/17) and tire tread (Cooper RS3-A) is probably the reason why the car suffers such drastic cold weather MPG drop. My Nissan runs 195's and I've never seen such drastic MPG difference between different tire pressures, but it's also FWD and has much less drive train drag.

So far it seems like the best MPG comes from warm tire pressures of around 43+psi.

Dash MPG vs Pump MPG

I added in the dash MPG in for kicks above, but it made me see another trend. In cold weather when ever my real MPG would get above 27mpg, the dash always underestimates, but if my real world mpg is below 27mpg the dash is usually optimistic. If I recall correctly, the dash mpg gauge works of injector duty cycles. The higher your duty cycle the more fuel you use, which is not wrong. But it seems like in real world, more fuel in right areas can actually mean lower overall consumption.

Using more fuel can also be attributed to higher throttle body opening, which reduces the engine's pumping losses (same way intakes and exhausts help with power increase). While in closed loop, your O2 sensor will adjust your air to fuel ratios to 14.7. As you add more throttle (more air), O2 sensor will tell the ECU to flow more fuel to keep the mixture from leaning out. When ECU tells the injectors to flow more fuel, injector duty cycle increases.

This is why you can't rely on the dash mpg gauge for actual testing. Sure fuel pumps have errors too, but you can minimize those by using the same exact pump and filling up the same exact way.

Sorry for the long post, I'm pretty stocked to finally get 29mpg in the winter, especially on over the mountain trip. Now that I know that tires were the main culprit with the winter MPG loss, I can move onto testing various AVCS, Timing, and Fueling changes to see what helps most.

So.. Would you still recommend disabling CL to OL delay?

Of course! It's a no brainier, it destroys your ring lands and shortens the life of your motor. I was willing to loose MPG just to have a more reliable motor, but as my testing has shown so far, I lost no MPG due to disabled CL to OL delay.

WRX guys might see a loss because they have the smaller turbo then legacy's do. But my 04 FXT has the same sized turob as the WRX's and I can't say I've seen any loss from CL to OL delay disable either, but my wife usually drives that car and she's might lighter on the throttle.

The only time I've seen the CL to OL delay help gas mileage was in very aggressive driving, where your in boost very often, the delay reduces your fuel amount and power (plus added extra detonation). But once again, I'm willing to loose 1-2mpg aggressive driving, just to have reliability. Calm driving CL to OL delay being disabled doesn't hurt the mpg, in my testing it seems to help your mpg.

have you ever looked into tuning VE? at least in the cruise range. might even be worth "poking" beyond what seems logical, and by that I mean not just tuning into the first VE "spike" you see/find, but seeing if there are others that might be better.

in engineering it's usually easiest to test only 2 or 3 "levels" of a parameter, and then extrapolate from there. which is easiest and probably will find a pretty good answer, but this approach might miss the better sweet spot. as in, if you test only two points, you can only assume the results are linear, where it could be a crazy 3rd order polynomial...

speaking of, I wonder if DOE analysis software would be useful for tuning... (I've got access to quite a lot of engineering analysis software tools)

also, VE doesn't always correlate to MPG directly, as seen in some of the tuning for MPG going on with E85.

just some thoughts I have that I figured i'd share. after I tune my tip-in and mess around with trying to fix my fueling harmonics, I will be starting to tune cruise VE (or MPG actually).

Sadly it's very hard for me to do a log for 2 hour road trip, plus romraider sometimes freezes up from too much data. For this reason I haven't done much with VE tuning yet. Once I stop being lazy today I plan on building 4-5 tunes. Then drive like 15 miles roundtrip on highway and log them for each tune, same road etc. This will let me see what tune has what VE and duty cycles and try to see what helps the fuel economy the most.

Most people go about VE tuning a little wrong for fuel economy. While higher VE is good for power, higher VE for fuel economy means more fuel is used up. I've heard plenty of people say that tuning for higher VE (calculated gauge in RR), results in worse real world economy.

Another thing I want to log/pay attention to is fuel pump duty cycles. On highway easy driving it stays at 33%, but when IDC goes over 12 it spikes up to 66%. Which means the fuel pump is now pushing around twice as much fuel pressure. I wonder if lower tire pressures forces the fuel pump duty cycle to stay at 66% more?

yeah, VE has always seemed to be the thing to optimize, but optimizing for minimal engine load might be best, and is what is most often discussed/compared in MPG tuning threads.

so like what you do already, changing AVCS angle and timing, but then use engine load as your output (at least for cruise scenarios).

ThrottleHappy seems to know a ton about improving fuel economy, I've been reading a bunch of his posts on RomRaider and he does talk about lesser VE = better economy due to less fuel used. He also talks about E85 being tuned wrong by most people hence stupid bad fuel economy, E10 is not that far behind. Hence I do want to test running richer too.

The idea that everyone now days seem to agree on, pumping losses is what kills the economy the most. That means, the more gauge vacuum the more pumping losses your engine has to fight with. This is another reason why winter MPG is worse, air is denser thus more oxygen is available per square inch. Which means that throttle angle is going to be less then in the summer to get the same AFR. Which means more pumping losses.

This is the kind of thing I want to test with different tunes, sadly I wont see a really warm day until March probably to compare to winter logs.

yeah, been reading the same threads. now if only E85 was locally available! makes me think ELH's (or anything better than our crappy OEM header) would be better too, pulses not colliding with one another constantly. if only I had the funds to test...

keep up the good work.

ELH should help indeed, and a few people have mentioned it too. I want to test them myself, but currently my goal is to see the max I can squeeze out of a fairly stock setup.

Sadly my oem downpipe is not really usable, since I ran over a deer. But I might reaquire one just to see how much worse it is then the STG2 downpipe.

yeah, VE has always seemed to be the thing to optimize, but optimizing for minimal engine load might be best, and is what is most often discussed/compared in MPG tuning threads.

 

so like what you do already, changing AVCS angle and timing, but then use engine load as your output (at least for cruise scenarios).

This is why the stock AVCS tables have that spike of high advance at lower rpm / load. It reduces VE for better economy and worse scavenging. This keeps more spent gas in the cylinder for a sort of EGR effect and cleaner emissions.

Correct that spike is for emissions, what's odd is, there is another hole in the tune, right after it, where it's 0 avcs for highway speeds.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/05LGTStockAVCS.png~original

On my stock downpipe and catless up pipe, having AVCS at 15* gave me the best MPG. Sadly that was before I was religiously keeping track of tire pressures and ambient temps. Thus I can't 100% the increase was from just AVCS anymore. Until I get a stock downpipe again .

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS15v11.png~original

With a stg2 downpipe (catted) and stock boost levels, running AVCS at 15* at 2000 rpm gave me a lot of knock cruising. I would constantly see learning views with a little bit of timing pulled in those ranges. I believe this is due to increased VE with a less back pressured exhaust. Which means MBT (minimum advance for best torque) lowered and now stock timing advance was hitting the detonation threshold.

I now run this AVCS table, this is with stg2 downpipe, stock timing and fuel, and WGDC tables reduced to produce same exact boost as stock. As you can see I had to reduce the 15+ AVCS to fight with detonation.

http://i160.photobucket.com/albums/t188/covertrussian/Cars/05%20LGT/ECU/AVCS/AVCS10DPv2.png~original

Finally got around to testing different tunes, logging, and getting the averages for all of the runs. I did roundtrip runs, to make sure there was consistency in hwy runs I couldn't have stop lights or accel/decel inconsistencies, thus I started and stopped logs while still going 70mph on the exit at the same points.

Constants:

Divorced Stg2 Downpipe

Perrin Inlet

GrimmSpeed Crank Pulley

Cold Tire Pressure: 42f/40r @38f

Ambient: 42F

13 miles roundtrip - Contains flats, small hills and one major hill (impossible to avoid in VA...)

I had to cut the names short to make sure the columns looked right in the paste below. Here is an appendix for non self explanatory items.

[b]AVCS 0*[/b] = Stock AVCS Map for 05 LGT
[b]DashMPG[/b] = MPG reading from the dash, manually reset everytime the logger was started.
[b]RR-MPG[/b] = Rom Raider has a built in MPG calculator, not 100% sure on how it calculates this
[b]g/rev[/b] = Engine load
[b]MAF[/b] = Airflow g/s
[b]PW #1[/b] = Pulse Width Cyl #1, sadly rom raider only had one cylinder
[b]IDC[/b] = Injector Duty Cycle
[b]VE[/b] = Volumetric Efficiency RR Calculated
[b]FP%[/b] = Fuel Pump Duty Cycle, stock tune has three options 33, 66, 100
[b]Timing[/b] = Total Timing post compensations (I disabled IAT based compensations to help with consistency)
[b]AVCS[/b] = Left banks AVCS advance
[b]PSI[/b] = Stock MAP sensor, do keep in mind that stock sensor can't read below -10, with that said it's still very inaccurate up to positive pressure compared to my boost gauge.

After each run I would get back to gas station and flash a new tune, forced IAM of 1 on all of the tunes to avoid the relearning phases. AVCS 0* = Stock 2005 LGT AVCS map. Bolted values are the theoretical winners in that category. These runs were all done with the stock timing map and fuel map.

[b]Item		DashMPG	RR-MPG	AFR	g/rev	MAF	PW #1	IDC	VE	FP%	IAT	Timing	AVCS	PSI	TPS	MPH[/b]
[b]AVCS 0*[/b]		[b]26.85[/b]	[b]31.91[/b]	14.53	[b]0.60[/b]	[b]29.45[/b]	[b]3.89[/b]	[b]9.48[/b]	[b]67.66[/b]	39.25	46.56	41.06	1.93	-6.01	[b]14.05[/b]	70.23
[b]AVCS 5[/b]		26.55	31.68	[b]14.54[/b]	0.61	29.81	3.94	9.64	68.32	39.84	47.93	41.15	4.39	-5.97	14.28	70.62
[b]AVCS 10[/b]		26.70	31.76	14.53	0.61	29.61	3.91	9.53	69.22	40.28	46.62	41.05	9.31	-6.17	14.10	70.38
[b]AVCS 15[/b]		26.70	31.75	14.53	0.61	29.59	3.92	9.57	69.89	[b]39.09[/b]	47.00	41.15	14.09	[b]-6.23[/b]	14.26	70.47

As you can see from that log, the stock AVCS map got the best calculated MPG, lowest g/rev engine load, lowest pulsewidths and injector duty cycles, lowest VE, and Throttle Position.

AVCS 0 run was the first run, with full tank, and by 50ign run (below) I consumed 6.5gallons (roughly 40lbs lighter), thus AVCS 0 run is the clear winner in this came.

I took AVCS 0 tune, and made two maps with different timings at 2800-3200 rpm (70mph range):

[b]Item		DashMPG	RR-MPG	AFR	g/rev	MAF	PW #1	IDC	VE	FP%	IAT	Timing	AVCS	PSI	TPS	MPH[/b]
[b]45IGN@70mph[/b]	[b]27.00[/b]	[b]33.04[/b]	[b]14.57[/b]	[b]0.60[/b]	[b]29.03[/b]	[b]3.89[/b]	[b]9.42[/b]	[b]66.93[/b]	[b]39.27[/b]	47.36	44.36	1.21	[b]-5.98[/b]	[b]14.07[/b]	70.01
[b]50IGN@70mph[/b]	25.95	31.11	14.52	0.62	30.45	4.02	9.81	67.53	41.20	46.65	48.55	2.16	-5.70	14.46	70.41

Winner is 45* advance at 70mph range. Heck it even racked lower numbers then stock timing map, ~41* at 70mph, which means more timing helped reduce consumption more.

At this point I was pretty hungry and wanted to test my newly created tune to see what it was gonna get. Drove 130 miles roundtrip, to the first city I usually drive to. Sadly during the second half of the trip it started down pouring. Fueled up 4.933gallons, which got me a mediocre 26.37mpg. I will admit the rain probably stole and mpg or two, even then I would get just under 29, which means not an improvement over previous tune.

Sadly this either my stretch of road is not diverse enough, I did pick a road with flats and hills to do a more of a real life example. Another thing could be, finding the lowest IDC, VE, and TPS might not be the best for real life MPG.

Sorry for yet another book, Feedback is very welcome, to help me decipher the averages

very interesting. so AVCS set to a high number (for cruise) seems to NOT be a good thing for MPG (or at least for your setup).

I like the method for testing these. only taking data at cruise, as opposed to an entire trip. did you remove datapoints where the engine wasn't under constant load (like when it hits a little dip in the road and "comes off" the accelerator peddle...)?

really gotta fix my tip-in so I can follow along.

I like how you say 'mediocre 26.37 mpg'. come on man. That still pretty good given it is an awd machine with a fairly good amount of power

That being said, I don't fully understand all these various variables yet. But as I mentioned before, my tune has timing set around 49 deg when I cruise. Have you tried going that high and see how it affects your mpg? I am stage 2.5 btw (avo intercooler, invidia catless up, invidia catted downpipe , 3 inch midpipe--no resonator--, stromung quadtip catback,grimspeed ebcs, cobb sf intake, perrin lcp)

Guess I should switch to more specific names, will update earlier posts with this.

City A = Front Royal VA, 130 miles roundtrip, Rountrip Elevantion: 1300 to 600 to 1300ft

City B = Charlottesville VA, 120 miles roundtrip, Rountrip Elevantion: 1300 to 2000 to 600 to 2000 to 1300ft

City C = Winchester VA, 150 miles roundtrip, Roundtrip Elevation: 1300 to 700 to 1300ft

very interesting. so AVCS set to a high number (for cruise) seems to NOT be a good thing for MPG (or at least for your setup).

I spent a couple hours looking through my spreadsheet and gathering and fixing this data...

Recent runs within last two weeks:

AVCS 0: 26.37mpg, 41F, 45* Timing, 280lbs, Tires 42/40psi, City A

AVCS 10: 28.72mpg, 37F, 40* Timing, 440lbs, Tires 42/40psi, City A

AVCS 10: 29.23mpg, 38-48F, 42* Timing, 440lbs, Tires 42/40psi, City B

Historical runs over last year (do note that my tire psi gauge was off, hence the high psi).

AVCS 0: 28.61mpg, 70-80f, 42* Timing, 440lbs, Tires 45/41psi, City A

AVCS 10: 30.26mpg, 64f, 45* Timing, 440lbs, Tires 45/41psi, City A

AVCS 15: 28.60mpg, 75-80f, 42* Timing, 280lbs, Tires 45/41psi, City A

AVCS 10 so far is winning, but that's with a stage 2 downpipe. Car seemed to have liked AVCS 15* more with stock downpipe. Sadly I don't have an AVCS 10 roundtrip run. Sadly these runs are no where near as consistent as my newer runs, there has been some hardware changes long the lines between the runs.

AVCS 0: 24.78mpg, 40f, 42* Timing, 440lbs, Tires PSI unsure, City C

AVCS 10: 27.79mpg, 30f, 42* Timing, 280lbs, Tires PSI unsure, Not round trip

AVCS 15: 29.75mpg, 88f, 42* Timing, 280lbs, Tires 45/42psi, City A

AVCS 20: 28.39mpg, 80-85f, 42* Timing, 280lbs, Tires 45/42psi, Not round trip

AVCS 30: 23.29mpg, 30f, 42* timing, 280lbs, Tires 45/48psi, City A

Interesting observation, with AVCS being at 0*, the car is not as torque on the highway, using cruise control to increase speed is very peaceful, no lunging forward like it does with AVCS 10 to AVCS 15.

I like the method for testing these. only taking data at cruise, as opposed to an entire trip. did you remove datapoints where the engine wasn't under constant load (like when it hits a little dip in the road and "comes off" the accelerator peddle...)?

 

really gotta fix my tip-in so I can follow along.

I didn't remove the deceleration portions because they would be consistent on every run, so no need to.

I like how you say 'mediocre 26.37 mpg'. come on man. That still pretty good given it is an awd machine with a fairly good amount of power

That being said, I don't fully understand all these various variables yet. But as I mentioned before, my tune has timing set around 49 deg when I cruise. Have you tried going that high and see how it affects your mpg? I am stage 2.5 btw (avo intercooler, invidia catless up, invidia catted downpipe , 3 inch midpipe--no resonator--, stromung quadtip catback,grimspeed ebcs, cobb sf intake, perrin lcp)

Compared to what I've been getting lately in the cold weather, anything below 27mpg is mediocre .

I tried 50* before, but it was not in a roundtrip environment. Which now days is the only way to really get reliable numbers due to everchanging road & elevations changes.

Looking back on my logs, I saw that 45* ignition timing with AVCS at 10* has yielded me the best MPG so far. Reason I skewed away from using 45* is because cold weather tire pressures stole more MPG and masked the increased timing gains.

Something to consider, and I found this out on my Nissan. More cruise timing is not always better. As your engine becomes more efficient, the timing you need to reach minimum advance for best torque (MBT) lowers. The fuel mixture will burn up much faster and the extra timing will now force the piston to fight the extra pressure.

On my Nissan after a better flowing intake manifold, 3" exhaust, turbo, and 6 speed (2700rpm at 70mph, while 5 speed used to be 3000rpm), I was running 30* max at 70mph, and would get 30mpg at best. I tried increasing the timing to 35-40*, but gas mileage kept on dropping. At that point I decided to think backwards and start reducing the timing. Once I reduced it to 24* max at 70mph I started getting 36-41mpg ...sure as heck surprised me .

The manufacturer will often run timing at cruise that gets worse mileage for the sake of emissions. Can't sell the car if it can't pass emissions...

Your 100% correct, and it doesn't matter to them if a car has slightly more emissions and drives 100miles more (thus effectively has less emissions per mile), it's all about those static numbers. Motorcycles are the next victims, with forced catalytic converters on them, they are getting worse fuel economy then carbed versions. Cat's themselves dont hurt the fuel economy (I never gained any noticeable MPG gains from cat deletes on any of the cars), it's the cold tuning to heat up the cat that usually does.

But this is why the same exact model that is sold in Japan or Europe gets better fuel economy. They do different kind of emissions testing (no emphasis on NOx like here), thus their cars are tuned different and usually get better fuel economy. See this car-bibles.com article under "The transatlantic conundrum".