E85 Tuning for MPG

[HawkZ28]

I'm currently working on maximizing my MPG on E85. The absolute best I've gotten for e85 MPG on the highway (2010 GMC Sierra 4x4x4door, 20 inch rims) has been 12mpg, most averaging 11.5-11.7 highway. I understand I'm driving a pig with probably slightly worse aerodynamic qualities than a refrigerator, but I believe it can be better.

That being said, looking at stock tunes and the Flex Fuel spark, I've been trying to grasp how much, when, and where to add and pull timing at CRUISING speeds- generally .32-.56 loads at 1800rpm at 75. I've also not been able to log any kind of KR to give me an idea that I've gone too far, another e85 challenge. Looking in the repo, it seems the only e85 tunes are for forced induction 5.3's.

I've picked up some MPG with aggressive DFCO, MAF only, some other tricks I did with my 3.5L 4x4 CC Colorado tune years ago to get 25mpg with stock tires. This PCM is just leaps and bounds ahead of the P12s and P10s I'm accustom to. I have only added a CAI, Denso IR plugs, and Taylor Thundervolt wires. The PO supposedly cammed the truck- which it sounds like it- but I have no idea on the cam specs and haven't had a chance to pull a valve cover and degree it for duration and lift numbers to cross at TSP's website for EOIT adjustment. The PO also wrote an abortion of a tune, but that's another story.

I'm not looking for somebody else's tune, just some guidance what to log or how to read the logs to give the engine what it wants as opposed to what I think it needs. Is there maybe a parameter to log and shoot for highest or lowest point that I'm missing? I want to understand what to look for and why, what to do when, and why, the same as I do MAF, VE, etc tuning,

[GHuggins]

Post the tune - log wouldn't hurt... You'll want to watch delivered engine torque or even instant fuel economy for timing adjustments... You can gain from injection timing and other tweaks in the tune besides spark... Even Dwell settings can make a slight difference...

[roastin300]

Drive steady state after a timing adjustment has been made and log calculated engine torque like he said above. I like to add like 2 degrees to the areas where I care about gas mileage on short trips. Datalog and review, then iterate. If you lose, then go back the other way.

Low loads/rpm with E85 tend to need LESS ignition timing than gasoline. Helps keep combustion/cylinder/exhaust gas temps higher and burn the next consecutive cycle more efficiently when there is not much heat in the chamber. At medium and high loads/rpms you do the opposite and put more timing in to improve the torque while watching the knock sensors (pretty much doesn't knock on E85 ha ha gotta love it).

Also look into things like making your deceleration fuel cutoff thresholds more aggressive, and lower the mV of the switching points on the O2 sensors. I usually get a little out of that. And as he said above, bump the ignition dwell up. I always have positive results doing that. Just dont go too far, you will cook the coils. Start by adding 10-20% extra to the table. I have gone as far as 40% in some areas without failure but I don't recommend it unless your cool with a coil replacement.

[10_SS]

Another great way to find peak timing efficiency under cruise with an automatic is try to find a rpm/load that you have when cruising... try to match that by brake torque sitting still in the driveway. If your lucky you will find the same rpm/load window by brake torque. Then all you need to do is add or subtract timing when holding this load/rpm in real time and see if RPMs increase or decrease.. .pick the point where RPM stops increasing and reduce a degree, that's your peak timing efficiency (peak torque using least fuel) as long as you dont have knock.. if so, reduce a degree until it stops.

Problem is with the current software is we don't have allot of control over manual timing... sometimes the Timing Adjustments in Special Tools works but you can only subtract timing you cant add it so you may have to add 5-7 into the main timing table then take it out using special controls to find your sweet spot. I do this with Megasquirt in realtime tuning, just like the old days of turning a distributor to find best idle timing... so fast, so easy. I also had a MSD Timing Knob in my old BigBlock car.. 0-15deg of timing control, would do the same thing by loading up the engine in gear, brake torquing, play with timing from inside the car.

Or, use a loaded dyno...

YOu can also do this for most of your timing/load curve at any point you can reach by brake torqing... maybe force trans to a higher gear to stop wheelspin. Your gonna create allot of heat from the torque converter so don't do it too long, and give cool down periods. With a manual trans youre kinda screwed.

You could also build a microcontroller (ARduino) to simulate the E85 sensor and use that to add or subtract timing in realtime... you could add/subtract as much timing as you wanted this way in realtime by turning a knob. You would have to setup your Main Tune and Spark timing to run in the E85 ratio you currently have then use the Flex Spark table to add the timing (or substract) depending what E85 % you are telling the ECU with your simulated Ethanol sensor (Arduino). I've done this part, pretty easy.

[07GTS]

hmmm dwell settings..? ive been wanting to see if they help with e85 but herd alot of story's about killing coils, i have increased it a little for cranking rpm's on e85 to help cold starts in winter but havnt touched any constant operating areas, can the stock coils (LS2) handle a bit as 10-20% mentioned is still safe for whole table or just cruise areas..? sounds best to not go too much at higher rpm's ?

[Area47]

hmmm dwell settings..? ive been wanting to see if they help with e85 but herd alot of story's about killing coils, i have increased it a little for cranking rpm's on e85 to help cold starts in winter but havnt touched any constant operating areas, can the stock coils (LS2) handle a bit as 10-20% mentioned is still safe for whole table or just cruise areas..? sounds best to not go too much at higher rpm's ?

you can get away with about 20-30% more in dwell settings in the right area's.

[HawkZ28]

Tune and log posted. Try not to be too harsh haha. Took a while to find a 'small' log that could be uploaded.

I added calculated torque to the scanner. When you say instant MPG, do you mean a PID/Math for the scanner, or on my DIC? I've tried doing that- did a stock timing plus 8* tune, and subtracted in the scanner. I could feel it, but didn't see the difference. It also seems pretty sensative in that a slight dip in the road causes the DIC to jump up or down 1-2mpg. I can't do EOIT yet as I don't know my cam specs. Hopefully once work slows down I'll have time to degree it so I can get EOIT dialed in.

I'm hesitant to mess with dwell for the same reasons mentioned by 07GTS- I don't want to burn up any coils, and the fact I drive 1-200 miles per day, I could cook them pretty quick.

I have DFCO set pretty aggressive IMHO. You can feel it pull fuel as soon as you lift off, even down at 25-30mph. I think that's often overlooked by a lot of us- seasoned rookies like myself and pros alike. The latest tune (uploaded) I messed with O2 switch points, adjusted the min down from 450, and max up from 450, as well as airflow modes. We'll see what happens with that. I know we aren't supposed to discuss the cruise which will not be spoken of, but I thought it was pretty much out on the E38.

One thing that comes to mind- what are we all calling low, med, and high load? To me, High load is .52-.64, medium being .48 down to about .32, and low being anything below that.....?

I'll have to try the driveway trick- dyno is out. Timing knob- I miss how easy my 86 Z28 was/is to tune haha. I think I can adjust initial by ear, adjust the vacuum advance, and change metering rods and springs in the 625 AVS Edelbrock faster than I can load a tune.....datalogging though and no hot parts to deal with, though....

That reminds me of going to the parts store for a new cap and rotor, and being asked by the kid why us guys with old cars always want the copper cap and rotor kits over the aluminum!

[GHuggins]

You can go up in dwell 5% no problem and never have an issue...

[HawkZ28]

5% across the board, or in cruise cells?

Also, has anybody constructed a pid to log total or main advance at highest torque? Was thinking about working on that while data logging on the way home, but don't want to reinvent the wheel if I don't have to.

[GHuggins]

No, but that sure would make things easier?

5% for 8v and up - no point in increasing the lower voltage areas. You can get creative and do up to 10% in just the cruise rpm areas, but your going to gain very little from this, so I don't go over 5% unless you have much better a/m coils...

[HawkZ28]

She's on factory square coils.

What I've gotten so far is logging FF advance, filter with engine torque but im stumped on going about filtering for highest torque values only. Any ideas?

[07GTS]

what i usually do is use the cruise and instant fuel usage on the display and adjust timing up or down then drive and see if it helps or not, also of u have a cam eoit can have a big difference espically if u have it wrong, thanks all for the dwell suggestions ill have a bit of a play

[HawkZ28]

I really need to degree my cam so I can tweak eoit. Tried tracking down the PO to get cam info via social media with no luck.

FWIW, my DIC mpg can and will jump from 16 to 12 to 20mpg due to slight dips in the road. Until I figure out something with the PID, I am just going to have to focus on one or two cells per day in the cruising areas and messing with them using delivered torque and backing timing out in the scanner.

I did load the main and Flex advance from a 2017 and picked up about .5mpg on the first full tank. I paste specialed my 2010 flex table to 2010 HO, and compared to the same on a 2017. All in, the 2017 was had more timing taken out and added where all the reading and advice say it should.

Isn't there a table/multiplier that determines how much flex advance to add based on alcohol percent?

[GHuggins]

GMTECH - John did a write up on flex fuel tuning... Just google why everyone is doing flex fuel tuning wrong or something like that - should help with your flex fuel tuning questions... Also might want to keep in mind that your steeling tables from a direct injected engines tune vs yours, so there's that too...

[HawkZ28]

I'll have to look for that.

I didn't know it was DI. Well sh!t. My thought process was later models have better fuel economy, so I could see how much a difference between 7 model years and the HO/flex tables made in stock form compared to 2010 stock.

Since I'll be going cell by cell anyway, I'm going back to the previous table I concocted.

[HawkZ28]

I noticed that the FF advance, in the scanner, is only pulling or adding 1*or less, when it should be pulling or adding a lot more. Ideas?

[GHuggins]

The flex fuel "multiplier vs. composition" controls how much is added or taken per alcohol content - this was in the thread I was referring to earlier that John made...

I set them up as - 0, .150, .575, 1 & 1, but that's me...

[Area47]

No, but that sure would make things easier?

5% for 8v and up - no point in increasing the lower voltage areas. You can get creative and do up to 10% in just the cruise rpm areas, but your going to gain very little from this, so I don't go over 5% unless you have much better a/m coils...

even at 20% increase in the wot regions is still well below the threshold for heat and abuse for the coils. I have ran my own stuff above a 20% increase for years and well abused at that lol

[HawkZ28]

I must have missed it in the spark section when I was looking. Had seen it before, but thought maybe I was confusing with the alcohol comp table, and was tired and getting late, so called it good.

I want to make sure I correctly understand the process for EOIT. I have all 0s on the rpm table, so I add or subtract in the ECT table until trims max out at negative across the board/cruising cells, correct? I haven't adjusted the MAF since starting with EOIT so all #s will be + or - based off my baseline OEM EOIT calibration. Does that sound correct?

[07GTS]

I must have missed it in the spark section when I was looking. Had seen it before, but thought maybe I was confusing with the alcohol comp table, and was tired and getting late, so called it good.

I want to make sure I correctly understand the process for EOIT. I have all 0s on the rpm table, so I add or subtract in the ECT table until trims max out at negative across the board/cruising cells, correct? I haven't adjusted the MAF since starting with EOIT so all #s will be + or - based off my baseline OEM EOIT calibration. Does that sound correct?

yea for starters make your boundary all 520 (its very advanced stock) then just lower the ect 110 until the trims go rich (maby -5 deg at a time or + if it likes it) and as soon as they stay as is its good then u have the base line where u know the evc is happening and u can then adjust the boundary above idle to suit cruise, it can be very engine setup specific to what it likes so just try a few things and if it goes bad just go back to the last good spot, lower ect delays it or raising boundary delays it, also can be good to disable the desoot mode too