MrLoki ... can you point me to where its documented? ... please?
your quote: "4A does have worse MPG than 2WD. That has been well documented"
How about page 166 of the 2017 Manual:
The Control Trac[emoji2400] system functions in four modes:
• 2H delivers power to the rear wheels only. The information display will momentarily display 2H when this mode is selected. This mode is appropriate for normal on-road driving on dry pavement and provides the best fuel economy.
• 4A provides electronic control four-wheel drive with power delivered to all four wheels, as required, for increased traction. The information display will display 4A when this mode is selected. This mode is appropriate for all on-road driving conditions, such as dry road surfaces, wet pavement, snow, or gravel.
• 4H provides electronically locked four-wheel drive power to front and rear wheels. The information display will display 4H when this mode is selected. This mode is not recommended for use on dry pavement. This mode is only intended for severe winter or off-road conditions, such as deep snow, ice or shallow sand.
• 4L provides electronically locked four-wheel drive when extra power at reduced speeds is required. The information display will display 4L when this mode is selected. This mode is not recommended for use on dry pavement. Use this mode for off-road low-speed operation or when extra power is required, such as climbing steep grades, going through deep sand or pulling a boat out of the water.
There was a year of the Expedition, honestly can’t remember what year, cause I didn’t own one back then that only had 4A, no 2WD. A coworkers wife had one, and they always complained about the terrible MPG. It was talked about a lot at one point. It just makes sense that it would lower MPG.
Let’s go over the 15-17 4WD and what is in play in each mode as I understand it.
The changes in this system happens in 2 places, the front hubs and the center Diff(Transfer case).
2H - Front Hubs unlocked - Transfer case sends zero power to the front Dif. There will still be some spinning of the front half shafts and driveshaft because even greased hubs and bearings will transfer some inertia.
4A - Front Hubs locked - Transfer case sends zero power to the front Diff unless there is slippage detected by wheel speed sensors. The front wheels are now directly connected to the front half shafts, front Diff, and front driveshaft. It takes added energy(drag) to move those components.
4H - Front Hubs Locked - Transfer case sends a more fixed percentage of power forward to the Front Diff, more like a classic 4WD system. Only should be used off road and in conditions like snow.
4L - Front Hubs Locked - Tranfer case engages lower gearing an sends a more fixed percentage of power forward to the front dif.
Hope that helps...
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