A mapping change of the ECU would be needed otherwise your foot would always be on the gas.
Nope, 4x4 is not such a parasitic draw that you need a larger engine.
Years ago when I bought a 2003 TDI Jetta from the dealer I asked about the possible future avalability of awd, he told me that with 90 HP the TDI "didn't have enough power to turn all four wheels", LMAO! I had driven there in a 1991 subaru that when new had 62 HP at sea level, I live at 6,200 feet, with losses for altitude and the subaru being 13 years old at that point I believe the engine was making less than 50 HP, and I've driven that car through hood deep snow more times than I can remember, but somehow 90 HP with 3 times as much torque from the TDI "isn't enough power to turn all 4 wheels"?
If MPG is a consideration then a 4x4 should not be an option.
I'd like 4wd, and I was to maximize MPG's
with 4wd, so the 4 cylinder is the only possible option for me, thats fine if you don't want one.
a 4x4 is going to cost in the MPG department.
Yep, I'm glad you agree with me.
I don't see that a moderately weighted 4-cyl 4x4 is going to do any better than 2-3 mpg over a V6 (assuming similar weights) - at most.
I think your numbers are pessimistic when it comes to the 4 banger, sailquik sees 22-23 MPG when driving heavily loaded in a 4 banger, the 4x4 V6 seem to get about 17 MPG, but lets run some math on your numbers, an improvement of 3 MPG is a %17 improvement, over 200,000 miles that will save you $5,300 in fuel with a fuel cost of $3 per gallon.
BUT, lets back up a bit, if sailquik can haul 5000 pound of cargo and still get ~22.5 MPG, how will an unloaded 4 banger 4x4 get 20? Do you believe that the 4x4 drivetrain will consume so much power that it will reduce MPGs more than hauling 5000 pounds of cargo? For a trans/geardrive unit to consume that much energy it would have to be exceedingly inefficient, so much so that it would be generating a tremendous amount of heat, and I don't believe that the 4wd system in the sprinter does that.
So, more reasonable math, V6 4x4 gets 17 MPG, I4 4x4 gets 22 and will save you $7,000 over 200,000 miles of driving, thats %15 of the purchase price of the vehicle, thats significant, and when fuel costs rise the savings will be even larger.
Also, we know that long tall NCV3 vans get 17-18 MPG, and the NCV3 long tall 4x4's get pretty much the same, 17 MPG, as there isn't really a hit on MPG when the 4x4 is paired with the V6 there is no reason to expect a notable hit on MPG if the 4x4 was paired to the I4.