I love this feature!!! Thanks for reminding me of it! I noticed when I accelerate I'm in the single digit mpg's, it's terrible, especially at low speeds. Highway is pretty good in the 20's and 30's. I wonder how accurate it is. If I just go on a flat highway I could possibly get 30 mpg. That seems crazy!

It's in evoscan under fuel consumption.

 

This is all amazing and way beyond my current understanding, excellent work you guys. Once I know how I'll be taking full advantage of all this.
I do have one question. If it's not insane/stupid.
In a quest for mileage would it be possible to tune the ACD ECU, according to load, to switch off a set of wheels at cruising speeds? Meaning go 2wd once you're at speed? Sending power to fewer wheels should theoretically save fuel?
Again I apologize for intruding in here.
Donovan

 

You're confusing how the ACD works. Here is a down to earth way of explaining how it works.

The transfer case is ALWAYS 100% of the time, NO MATTER WHAT, sending power to the front and rear wheels at a 50/50 split.

The ACD is the regulator that decides how much the front wheels and rear wheels can differ in speed. When it locks up 100% it's completely forcing all 4 wheels to turn at the same speed. Just like a truck, you will skip and pop the drivetrain if you try to turn sharp on dry ground. Now the stock tune on the ACD never locks it that much because it would cause damage if you turned and there's no need to keep it locked when the system can respond so quickly.

So the maps decide how much it locks/unlocks as G-Forces, speed, and steering angle change.

If the ACD was 100% unlocked, the rear wheels and the front wheels can spin at any speed they want without *any* regulation from the differential. But note that this is NOT the same as "unlocking" the rear wheels when applying power.. The Transfer Case controls the lock, and it's always 50/50 no matter what.

So what happens is that when the ACD starts to lock, if the front wheels are spinning less than the rear wheels (for instance when turning since they have a shorter path), the allowed difference in speed is reduced and the ACD will apply a certain amount of locking force that makes some of that momentum shift the to rear as it tries to make the two inputs rotate at the same speed.

The key to understanding this is that how much the ACD locks determines in a round about way, how much extra "spin energy" moves from the front to the rear and vise versa. I use that term because it's not the torque that we're applying with the motor. It's the *already existing* difference in wheel speed. If the front wheels are spinning 55mph and the rear are spinning 53mph, it can lock really hard and quickly make the front slow to 54 and the rear speed up to 54. It would almost instantly jerk the car in the middle of the turn as it quickly forces all the wheels to spin at the same speed. If it locked up slowly and over time, the energy transfer would be smoother and not exert as much force on the wheels, which can effect whether they slip or not. So technically the car *is* moving torque to the front and rear, but not directly from the motor. The road through wheel slip and turning angles, has to make the wheels spin at different speeds before the ACD can move that energy around. Sometimes that means lots of power quickly going to the front, sometimes it means lots of power going to the rear. But when the motor applies power it always goes 50/50 to all four wheels!

No matter what when you apply throttle, the transfer case applies 50/50 torque to all wheels. The ACD decides what the allowed difference in speed is before it forces the energy to "equalize" and how smooth it does this determines whether you're oversteering/understeering or applying harsh 4x4 power, or slip resisting power that goes to whatever wheel can find traction even if that means the other tires are spinning at different speeds.

I hope that makes sense. I never found anyone able to explain it in such simple terms when I was trying to figure it out.

 

Well according to evoscan I am averaging 36-38 MPG on the highway.

 

So what happens when the ACD pump fails? Then does the power lock to the rear wheels?


So your saying there is a way in the tune to reduce the oscillation of the a/f during closed loop? If so how?

 

The pump is used to make the differential lock. So without the pump, it cannot lock?

I think it just goes to an open state, but mine has never failed so I'm not 100% sure.

 

@acidtonic
Dude, that is the best explanation for anything ever! Thank you.
There should be a sticky full of those explanations specifically for our cars. It'd save me saying some pretty stupid ****.

 

When the pump fails the diff is stuck in an open state. The pump is what allows it to lock.

 

When pump fails, you also burn up the ACD if you keep driving. Ask me how I know.

 

Oh great, I've been driving on a dead pump for a month or so -.- Don't see how that would burn it up though, if it's always in an open state?

 

Shep said my ACD was burnt up because of that. I think a previous owner drove around for a while until replacing the pump. I don't have any warning lights or codes but my ACD is still burnt up. I'm guessing its because there is never any hydraulic pressure on the unit, so the clutch pack constantly slips. Theres really no other way to kill the ACD. Funny thing is it still worked though. But I dunno I've never experienced a good ACD unit I guess.

 

Is anyone else getting a p0300 with high cruise timing?

 

Never got any codes for the higher timing. But how much high timing are you running?

 

+1. No codes for me yet.

 

Im at 42* during cruise.