Tuning for Fuel Economy

[Flinkly]

just to add more parameters to log, maybe your coolant temp is dropping down and effecting fueling. i still keep thinking of somehow making/adding a homebrew grill louvre system for shorter winter warmup and better cruise efficiency/drag.

 

Sent from my XT1028

[xt2005bonbon]

I rebuilt all of the calipers yesterday due to a stuck piston. Had to go to DC area, around 130miles each direction. I usually fill up once I get into the area.

 

Going there I got 29.03mpg with average ambient temp being 60*F, this is up compared to last couple highway trips. Coming back I got 26.67mpg with average ambient temp being 50*F. Which is odd because returning I usually get better mpg. Tire pressures pressures were within .5psi between cold and 1psi warm, thus I don't think they are a factor.

 

How does this tie into ecu tuning?

Every time it would get below 60*F my gas mileage would drop, come to think of it I've never gotten more then 27mpg when temps are below 60*F. Car felt a lot more powerful just cruising at 70mph and would lunge forward when accelerating with cruise.

 

I got some logs to parse, but will have to do a warm day log with same parameters to see how different the load looks.

 

Do you still get her into boost once in a while during your highway drive?

[covertrussian]

just to add more parameters to log, maybe your coolant temp is dropping down and effecting fueling. i still keep thinking of somehow making/adding a homebrew grill louvre system for shorter winter warmup and better cruise efficiency/drag.

 

Sent from my XT1028

 

Coolant temp was in 190's from my log. Which is kind of warm for a ~50*F IAT temps/45*F Ambient (Ambient is -5*F from IAT usually).

 

I believe the primary CLT enrichment table is "Min Primary Base Enrichment 1", which stops adding fuel after 122*F coolant temp.

 

Timing has IAT based compensation which is 0.0* at 68*F, and 1.05* at 50*F.

Fuel compensation doesn't exist from what I can tell, but there is a MAF Compensation (IAT). Which is 0.0 at 68*F, next column is 32*F and compensation varies by g/s. Thus it doesn't seem like that's the culprit.

 

Wastegate does have a 50*F IAT based compensation, it pulls -4.7 duty cycles, while at 68f it's at 0. Which is odd because it felt like it added and not pulled duty cycles .

 

Do you still get her into boost once in a while during your highway drive?

 

Not if I can help it, but with the tiny turbo and 3k rpm cruising it gets to 10psi if your not careful when trying to pass a car. I noticed that if I tap the cruise add speed button it doesn't go above 0psi. While if you press and hold it for even 1 second, it will hit 10psi in no time.

 

I live and drive in Virginia where you get a class 1 misdemeanor and a $1500 fine for going 80mph. Luckily they raised the speed limit to 70mph, which means I can speed up to 75mph to pass cars, but I cruise at 70 since all of my highway testing has been at that speed so far.

[covertrussian]

Anyone have any ideas on why slightly colder weather has a such effect? I've been looking over the tune and just don't see anything that would make it be more powerful from compensations stand point. It just seems too powerful just for having colder air, I feel like something else is at play.

 

Wastegate does pull 4.7 duty cycles, but I'm already at 0 at those ares, so can't get any lower.

[iNVAR]

If you look at your MAF (g/s) reading in a datalog for a given pressure at a given RPM (say 18 PSI @ 4000), you are ingesting more air during colder temperatures. Cold air is denser.

[Flinkly]

but at cruise, the throttle plate would be adjusting for the change in density. overall, no matter the outside temp, the same "load" is needed to keep a subie moving at 70mph. i think reduced efficiency would be a more likely cause, from a colder running engine. more heatloss to the outside causing less efficient use of gas.

 

we need grill louvres (for subies not equiped). closed for warmup and cruise. decreased drag, increased efficiency. would even force more air thru the tmic, so even denser air for more power (to justify it to the non-efficiency minded turbo subie crowd). also better mileage means saved gas funds, to use for more mods!

 

Sent from my XT1028

[iNVAR]

but at cruise, the throttle plate would be adjusting for the change in density. overall, no matter the outside temp, the same "load" is needed to keep a subie moving at 70mph. i think reduced efficiency would be a more likely cause, from a colder running engine. more heatloss to the outside causing less efficient use of gas.

 

we need grill louvres (for subies not equiped). closed for warmup and cruise. decreased drag, increased efficiency. would even force more air thru the tmic, so even denser air for more power (to justify it to the non-efficiency minded turbo subie crowd). also better mileage means saved gas funds, to use for more mods!

 

Sent from my XT1028

Oops, sorry, I didn't read his earlier posts about having reduced fuel economy. I was only addressing the part where he asked why the car produces more power in the cold, which is explained by air density.

[covertrussian]

iNVAR, you bring a valid point still with g/s being higher. I wish the temps would warm up so that I could do a log with more items logged (my existing logs don't capture enough info).

 

Flinkly, my water temps were actually pretty high for those temps (at 190*F). Thus it doesn't seem like it's that.

Edited November 17, 2014 by covertrussian

[Flinkly]

Flinkly, my water temps were actually pretty high for those temps (at 190*F). Thus it doesn't seem like it's that.

 

You're temps are still normal internally, but you and the cold are both taking more of the engine's heat (energy) than on a "nice day". You're blasting the heat to stay warm inside, and your engine is losing heat thru the oil pan and block (and the radiator, etc.). The engine is maintaining a reasonable internal temperature, but it's using more energy to maintain that then normal, and thus has less energy to put to the ground.

 

Even your exhaust is flowing less due to the outside temps robbing the exhaust of more heat energy, increasing your exhaust gas's volume, which reduces your exhaust gas's velocity. This is why we ceramic coat and wrap headers and uppipes, to keep velocity high for the turbo. And coat and wrap downpipe's so that the turbo/engine doesn't have to work any more than it needs to push the exhaust out the back end.

 

and obviously, i'm simplifying things here, but it's true.

 

Also, i'm not saying that there aren't tuning parameters that are reducing MPG either, just saying that they aren't by any means the only culprit. but maybe I should keep this talk somewhere else since this is specifically for "ECU tuning for Fuel Economy", not "modding for Fuel Economy".

[covertrussian]

While I can see that hurting economy in general, I don't think that's what I'm seeing in this case. Which by the way, our aluminum blocks are worse for economy compared to cast iron blocks, but they sacrifice gas mileage for performance/weight.

 

You know how going 75+mph it feels like your in boost just cruising? That's basically what it felt like going 70mph in colder weather. Now on the forester forums someone mentioned that colder air is denser thus requires more power to go through. I could almost see that being the case, but the Legacy is far more aerodynamic then the forester.

 

The reason I started this thread as an ECU tuning for economy because when it comes to regular mpg threads, people just end up saying mod your right foot... I might change the name of the thread though.

[Flinkly]

hmm... there does always seem to be two sides to each coin:

 

Colder (Denser) air means more engine power, but increased drag.

 

I can believe it, and I agree that the boxy forester is for sure less aerodynamic. in essence, you'd still be making the same increased power from the colder air intake (as a forester would), with less drag then them whether it was cold out or not.

 

also, I assume you already know almost all the stuff i'm saying. I mostly put it in writing for everyone else and to further the discussion.

 

and my MPG appears to be on the way down for the year. I have been tuning for the last couple months though, so I think my MPG is suffering from that a little as well. but the cold sure isn't helping. at least my linear trendline of the last 3-4 years shows a healthy increase in MPG. just gotta keep the slope positive.

[covertrussian]

Indeed, I'ver never considered the added drag from denser air, but it does explain the engine working harder. I've noticed similar trends with other cars while driving at night (colder then day). You can feel the engine just working harder (like going up a hilly road).

 

With the LGT, the best way to explain it is try driving at 3200rpm in 5th, even though off throttle you will be out of boost, but it will go into boost much easier as soon as you tap the throttle. I think the cold weather basically makes it get into boost easier.

 

Sadly the stock MAP sensor doesn't read accuractly in vacuum and doesn't read below 10in/Hg at all, thus I don't have logs on vacuum numbers while cruising. But I do think it stuck around 10-15in/Hg a lot more, where before it would be 15-20in/Hg.

 

AFR's where fine (~14.7), but they are just a ratio. Hypothetically at 10in/Hg you are flowing twice more air then at 20in/Hg, thus the ECU would add twice as much fuel to keep the AFR at 14.7.

[Flinkly]

hmm, maybe I should add my boost(vacuum) gauge to the parameters I log...

 

I do pay attention to what it says, and have solved a few blown hoses that way. I wonder how accurate it is in vacuum, or boost for that matter.

[covertrussian]

Do you have an electric gauge? I'm tempted to use an electric one just so that I could log the data.

[Flinkly]

plx boost gauge. I bought it more just to keep an eye on things when I went stage 2. bought alongside my plx AFR guage/sensor. should probably remove all the extra hose I have between the manifold and the sensor. I just connected it up and left the extra in case I needed it, and never removed it after I got it all in place and working. probably an extra 3 feet of 1/8" ID hose...

 

both can be logged in romraider, alongside normal ECU parameters, but I've never considered logging boost/vacuum. I've already got romraider connected with my AFR for when i'm interested in logging that.

 

http://www.plxdevices.com/product_info.php?id=SEMOSMVB

[covertrussian]

The problem I'm running into is not enough USB ports for all of the things I need to log. Almost wonder if there is a logger box that we can send the data to, and then one connection to the computer.

 

My Nissan ECU (NismoTronic Nemu) has a small breakout box with 4 inputs (WBO2, MAP sensor, IAT, etc) and it sends the data directly to the ECU. That's how I ran Speed Density with an aftermarket sensor, and that's how I run Wideband Closed Loop (only have one sensor wired in the car, just the MTXL).

 

 

hadvw, I would say your issue is unrelated and you are better off starting a new thread to get the proper attention. Asking mods to move your post.

Edited November 18, 2014 by covertrussian

[Flinkly]

I've got a 4 port usb hub in the dash, and the PLX sensor modules daisy chain together, so you can link "a lot" together and only have one USB cord/connection.

 

My basic setup is tactrix plugged in at my feet, USB snakes up to behind my cubby gauge pod, where I have my two PLX sensor modules and USB hub, then 1 USB cord comes from the hub and goes to my center console box. in there I redid my AUX "panel" to include a cute little Molex Wiring key and a female USB plug end (the wire from the 4-port hub in the dash).

 

The Aux is still usable, there is a little hole where I can plug in a molex connector/key and flash ROMs (it connects my green test connector, cause I got REALLY tired of connecting/disconnecting that thing... and my wife got tired of seeing it at her feet) and the female USB plug end for inserting a USB cord to my laptop to log or flash.

 

I used to have a USB jack on the face of my gauge pod, but the wife didn't like the way it looked, and REALLY hated when I plugged the laptop in and set it in her lap...

 

she hates the gauges too, but those aren't going anywhere.

 

which reminds me, I need to do update my build thread for the little AUX panel redo...

[covertrussian]

Good idea, I have to end up doing a USB hub once I have more things to log. Would hate to have 4 serial to USB adapters.

 

I thought I did more AVCS testing in the winter, but looks like I started going above 10* cruising after 60F+ weather hit in. Guess I'll try out 15* advance, with downpipe and in warmer temps I didn't see any more MPG gains past 10* AVCS.

[covertrussian]

Found another interesting thread from Outback forums. Seems like NA Forester/Outback guys are more concerned with improving fuel economy, I just like having a fun car and getting good mileage .

 

Take aways from thread:

- Post 24 - Colder dense air = more fuel needed, but with more fuel comes more torque, thus in theory less throttle is needed.

- Post 58 - Heated seats causing extra electrical drag, I've been wondering about this one too, wife loves to use them, and I think I'm seeing a correlation.

- Post 49 - 2013 Outback and 2010 Outback both loose 4mpg when temperatures go below 55*F on same tank full. This is exactly what I'm seeing, perhaps it's the way Subaru does MAF tables.

Edited November 19, 2014 by covertrussian

[Flinkly]

I just found it (in the tune, but have always seen it), and not sure if your tune has it, but my 08 runs at 14.4 AFR at idle. it's got -.441 in the closed loop table A in the 850 RPM row for .2 and .3 g/rev. save some gas at idle/coasting.

 

and just thinking about it while posting, but is idle above 850 when temps are below 60? might account for some reduction in MPG at lower temps. idling at higher AFR. I'll check on this the next time I have my tune open in Romraider...

[xt2005bonbon]

I recall that our car usually does not idle at 14.7 but more like 14.2-4. Someone on here (I think it was Heiche) found a way to fix that. I'll find the thread. I pointed my tuner to it and it did the changes.

[Flinkly]

yeah, it's just a closed loop "compensation" (or additive?) vs load table A and B. B was 14.7 idle, but A had a 14.4 idle. I think it's better to have it lower though, for MPG. no need for moar power at idle. could probably go lower...

 

now for tuning, I did bump it up to 14.7, so that I could do a better job of tuning. the change from 14.7 to 14.4 at idle has been messing with me.

[xt2005bonbon]

Yeah that's it. Here is the post anyway for anyone wondering..

 

http://legacygt.com/forums/showpost.php?p=4570249&postcount=12

[covertrussian]

Nice I'll check that out. Also Subaru factory O2 sensor seems to read lower then my wideband. 14.7 is read as 14.2 by the Subaru O2.

 

I did a bunch of mechanical changes (new used injectors, Switch to Rotella T6) to the car and wanted to see if gas mileage was the same. I unplugged the Radiator Fan 2, because it keeps on running just about always. This still got me 190*F coolant temps at 25-30*F ambient.

Got 26.1mpg, which is once again similar trends to cold air MPG. I don't think it's winter fuel responsible, because my city gas mileage is up to 19.5mpg if I do all of the miles in 3 days instead of usual 7 (reduces cold starts), usual 7 day summer MPG is 18 at best.

 

Next testing items:

Increase IAT's - Block off intake and hood scoop to increase IAT's and see if MPG goes up. If it does that means, it's not winter gas or denser air making increasing drag, which means it's something in the tune based on IAT.

Increase AVCS - See if denser air likes more AVCS, if it does then I really wish there was IAT based AVCS compensation .

[covertrussian]

yeah, it's just a closed loop "compensation" (or additive?) vs load table A and B. B was 14.7 idle, but A had a 14.4 idle. I think it's better to have it lower though, for MPG. no need for moar power at idle. could probably go lower...

 

now for tuning, I did bump it up to 14.7, so that I could do a better job of tuning. the change from 14.7 to 14.4 at idle has been messing with me.

 

Alright saw this on my 05 LGT. There is only one closed loop comp table on 05-06 LGT's. I wonder if they put it in there due to the uppipe cat, which would help it be happy and warm at idle.

 

Also my assumption of stock sensor being off at 14.7 was wrong. I was basing it on the idle numbers. I did a fairly decent highway drive logging my UEGO and stock sensor, and the values where very close to each other (Uego AFR's being delayed because it's post turbo).