Tuning for Fuel Mileage

[bradearlywine]

On a gas engine, if you are under boost your adding fuel because you need more fuel to maintain desired afr. Of course there is always a trade off between efficiency of the engine, clearly making more power under boost due to better VE. Everything is a little different with diesel. Diesels control engine speed and power output with fuel only, and as such lean is actually cooler so no potentially damaging heat related effects from lean.

Diesels with VGT, specifically a 6.0L in my case, has about 7lbs of boost driving down the road at 70mph or more depending on your VGT controls. How does boost effect fuel mileage driving down the road? On diesel, I would assume 30mg mass fuel at 7lbs of boost to maintain 70mph would be harder and less efficient than 30mg mass fuel at 3lbs of boost to maintain 70mph, just due to backpressure alone. I understand the advantage of more boost under cruise so that it will build boost quicker if you were to say go WOT, but would less boost and less backpressure be more beneficial for MPG? These numbers are just examples.

I know that EBP is directly effected by injection timing, and so is MPG. Most gas engines don't have VGT turbos. It would seem that opening the turbo some under cruise would reduce pumping losses. Since the diesel is naturally lean at cruise, the loss of VE from less boost should be neglible.

Hoping some advanced tuner could help bring this into perspective for me.

[RandomEnthusiast]

Injection timing and scaling back pedal map and mass fuel desired went from 16 hwy on 06 250 to 19hwy on same truck. I scaled it back by about 15% fuel wise and bumped timing 2 degrees.

[bradearlywine]

Injection timing and scaling back pedal map and mass fuel desired went from 16 hwy on 06 250 to 19hwy on same truck. I scaled it back by about 15% fuel wise and bumped timing 2 degrees.

Awesome, Ill give that a go. As far as my original question, I went out datalogging with IDS today. With IDS, I am able to control VGT DC on the fly and watch how it effects boost, ebp, and mass fuel desired. I'm pretty amazed at how much difference there really is.

Fully warm truck. Tests at 50mph. Going from 85% DC at steady cruise, MFD would hit around 43. Dropping it to 0% would increase speed, so you had to decrease throttle achieving same speed around MFD of 26. At normal VGT of around 55%, MFD is around 35. That's a saving of about 25% over stock, and more over more aggressive tunes trying to build boost quicker.

That wasn't all I found. Even a rolling takeoff at low throttle required 10 less MFD at 0% VGT over normal VGT to achieve *near* same acceleration rate. The truck actually feels like it has more power at low RPM low APP even though there is literally no boost. Once you pass about 30% throttle the truck has no guts. The only difference is exhaust backpressure really.

Clearly, it seems some fine tuning adjustments can be had. Finding the best balance that still has enough boost on reserve at cruise for when you nail it, but low enough for better economy.

**FYI IDS is not measuring MFD at mg. I think it may be micro pounds, but I will have to go back and look one day**

[bradearlywine]

So I did a little tune modification. Basically multiplied all cells below 36mfd EBP desired by .8, to reduce by 20%. Some real world log numbers. I cant be too scientific, we have a lot of hills around here but these were taken during limited flat areas. The other variable that changed was injection pressure. I know higher boost levels help mix the fuel, so to counteract lower boost numbers I slightly increase injection pressure at those mfd areas, around 150psi. FICM unmodified. I forgot to verify the exact PW on the injectors while taking data, but I went back and looked where I believe the data point was set, the new tune was about .2 MS less average for what its worth.


NEW TUNE FIRST

RPM 1974 - 1712 - ?
APP 19 - 17.5 - 7
MPH 68 - 59 - 30
VGT 50 - 54 - 52
EBP 23.9 - 23.1 - 17.1
MFD 22.6 - 21.1 - 10.3
PSI 5.4 - 4.9 - 1

VS OLD TUNE

RPM 1726 - 1744 - ?
APP 19 - 20 - 10
MPH 59 - 60 - 31
VGT 56 - 56 - 60
EBP 27.2 - 28.2 - 19.5
MFD 24 - 25.6 - 13.5
PSI 6.9 - 7.5 - 2

[qwkvert]

Good stuff man. Thanks for sharing what you're learning.

[bradearlywine]

Good stuff man. Thanks for sharing what you're learning.

No problem. I'm just messing around, trying a few things. I'm sure this stuff isn't new, or even secret, but it doesn't appear to be shared much. I'm guessing the guys that know aren't telling. I use many different forums for information, and I try to share what I learn. I even run a website with articles on the 6.0L, but mostly the 5.4L. http://www.expertswrite.net

These trucks could use all the help they can muster in the mileage department. If you can increase mileage at cruise while still providing good performance when more demanded, everyone wins lol. I noticed a slight turbo lag when stomping on the pedal from a roll, but it lines up really well with how long it takes the trans to downshift. Before, maximum boost was achieved before the shift could finish. Now it is just getting to peak after the shift ends

[RandomEnthusiast]

That's awesome. Hopefully you can figure out more stuck. ATM I don't have anything to test anything on so yay me.