...

 

I don't think at this point in time enough fuses have been pulled, and pulled for a long enough duration, to give you the affirmative answer you seek. Wait a year or two.

 

Bill Winney:
There is "only" one Ford Workshop manual that explains PTU/4WD operation, nothing different or special for a FEH.

BillyK:
A while back you mention rear wheel torque at times when you shouldn't have any. You shouldn't have "any" rear wheel torque once you reach a constant speed unless your on ice, snow, etc. I've never seen anything as high as 40%, ever! From a dead stop, all the way to the floor shows maybe 35% at the most. One thing that I'd be curious about is to disconnect two of those SGs and use one with basic PIDs with one set to 4WD.

Where does the 40% come from? Not exactly sure what you mean. It's a 12V duty cycled at 1kH. If you 12V all time, it would show 100%, half the time 50% and so on.

If I'm on your ignore you won't see this anyway!

 

Bill W: I completely understand your concern. If you'd like to know for sure whether or not the PTU gears are spinning and still being lubricated, loosen the PTU vent bolt and see if any leaks out on a 20 mile highway speed trip with the PTU fuse removed. This will give you a definate answer of whether or not the PTU is still being lubricated. Just be sure to top off your PTU again and tighten the vent bolt when finished.

Since I bought my MMH, I never pulled my PTU fuse. 54,000 miles on it about a month and a half ago and my PTU failed and needed to be replaced. I've been researching ways to keep this from happening again and decided to pull my PTU fuse during the summer months.

Billy K: The 40% of the time comes from: 95% of my driving is back and forth to work (8 miles - 15 minutes). Using my son's flip video recorder, I recorded my SGII on that trip and found that a little over 6 minutes of my 15 minute drive, power was being applied to my rear wheels (no highway driving, bi-directional roars with cross roads, curves and hills). I believe this contributed to my PTU failure. I also believe that TSB 09-4-4, the loose PTU vent bolt, caused the fluid level to drop which decreased the cooling of the PTU which also contributed to the failure. When my PTU was replaced, the dealer stated that I abused it and they were not going to replace it under warranty. I know I didn't abuse it so I wrote a letter to the Service Manager explaining the above and he forwarded it on to Ford who agreed to replace the PTU under warranty.

wptski: It is good to know that the clutch is in the rear and not in the PTU. What has me baffeled is that when underneith, I don't recall seeing any wires leading to or from the rear drive system which would indicate any electronic control of the torque to the rear wheels. This is why I assumed that the torque was adjusted by the PTU or from the transmission to the PTU. I'll look specifically for the wires next time I'm under it to make sure.

All: It is because I had my PTU fail prematurely that I am searching for a solution to prevent my PTU from failing again.

 

There seems to be a lot of instances of premature PTO/PTU failures, along with lubricant seal faulures. I suspect the seal failures are the result of the PTO/PTU overheating and boiling the lubricant thereforce "blowing" the seals. I find it interesting that the same system in the Mazda CX-7 seems to require aditional cooling via routing engine coolant through the PTO/PTU case.

The earlier Escapes had a temperature sensor in the rear coupling clutch that was used to trigger an overheat warning to the driver and the advice was to not make so much use of the 4WD system. If that didn't work then the 4WD system would be entirely disabled and the driver advised to pull over and allow the system to cool down before proceeding.

I would have thought that by now Ford engineering would have at least revised the 4WD control firmware to make less use of the system and therefore reduce or alleviate some of the failures. But then given that FWD an F/AWD system are so potentually hazardous if wheelspin/slip develops I guess I can understand the desire to apportion more engine torque to the rear wheels in order to help prevent instances of loss of directional control due to too much torque being applied to ONLY the front wheels.

It seems they either need to "beef-up" the PTO or provide cooling as Mazda had done.

 

I'm a native of the Badger state and lived there a number for years. The reference to "driving in hills" caught me because in the terrain is significantly more vertical in Pennsylvania than in the Midwest. I have not heard at the workplace or local dealership of an epidemic of blown PTU's in the Ford Escape vehicles. Heck, everytime one presses on the gas pedal, regardless of terrain, torque is sent to the rear wheels in these vehicles. I'm not buying into the statement, driving in hills will blow your PTU. I'm more interested in why the PTU vent bolt is loose?

 

The connector is right on top of the rearend and somewhat difficult to see! I was going to disconnect mine one time but though since I can hardly see it, how am I going to reconnect it??

I once was considering installing a switch to defeat the 4WD but then the "wrench" icon would be ON all the time and possibily masking another problem! Another way would be to install a dummy resistor on the output of the 4WD module with a switch to fool the module to think that it was still connected. Just too much work!

Believe me, the PTU is roatating all the time. Maybe I can grab a paragraph or two from the manual's theory of operation, if you like?

 

The statement of the hills was to explain why my rear wheels were receiving torque 40% of the time while I was driving. Driving up hills would not cause the PTU to fail; however, this combined with the vent bolt leak is what caused my PTU to fail. It overheated and burnt the oil (that was remaining).

By looking in to why this occured, I was also looking at ways to prevent it from occuring again and what better way to prevent another failure than to not use it when it is not needed?

I've attached TSB 09-4-4 which describes the solution. Verifying fluid levels and making sure the PTU vent bolt isn't leaking should prevent the PTU from failing. Removing fuse #35 in my 2007 MMH yeilded good results and an increase in MPG so I was attempting to share what I have learned.

 

From '07 FEH/MMH Workshop Manual.

Principles of Operation
The vehicle is equipped with an intelligent 4-wheel drive (4WD) system that is always active and requires no driver input. The system has no mode select switch. The system combines transparent all-surface operation with highly capable 4WD, and is capable of handling all road conditions, including street and highway driving as well as off-road and winter driving.
The 4WD system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is sent to the front wheels. If wheel slip between the front and rear wheels is detected, or if the vehicle is under heavy acceleration (high throttle position), the 4WD system increases torque to the rear wheels to prevent or control wheel slip.
The 4X4 control module varies the torque sent to the rear wheels by varying a pulse-width modulated current to the clutch in the rear axle. The 4X4 control module also provides the brake system with its current clutch duty cycle and whether or not the brake system may take command of the clutch duty cycle.
NOTE: The active torque coupling is not repairable. If replacement is required, the active torque coupling and rear axle are replaced as an assembly.
The PTU is a gearbox that attaches to the transaxle.
On automatic transaxle vehicles, the RH halfshaft passes through the transfer case and engages the differential side gear as in normal FWD applications. The transaxle differential drives the PTU.
On manual transmission vehicles, the PTU is directly driven by a gear in the transmission. The halfshaft/intermediate shaft connects directly to the transmission differential by passing through the PTU. The PTU then drives the driveshaft at all times. The driveshaft drives one half of the rear axle clutch pack. The other half of the rear axle clutch pack drives the rear axle ring and pinion.
NOTE: PTU repair is limited to seals, gaskets and output flanges. If any of the geared components, bearings, case cover or internal shafts fail, a new transfer case must be installed.
The PTU is sealed from the transaxle and has its own oil sump. The PTU on an automatic transaxle vehicle uses 355 ml (12 oz) of SAE 75W-140 gear lubricant. The PTU on a manual transaxle vehicle uses 350 ml (12 oz) of SAE 80W-90 gear lubricant.
The active, on-demand 4WD system uses data from other systems as inputs to the 4X4 control module. The 4X4 control module uses the inputs to determine the appropriate amount of current to send to the active torque coupling that delivers the desired torque to the rear wheels. Specific inputs to the 4X4 control module are:

 

"....vent bolt isn't leaking..."

Some years ago the rear differentials were "vented" in this same way. More recently the rear differentials are vented "remotely", a rubber hose from the differential case vent point off to some higher point on the body frame.

The vent bolt, by design, should be well above the high point/level of the lubricant when it is most heated. In order to have the most cooling efficiency the lubricating oil must be kept filled to maximum capacity.

So the only thing wrong if the oil is leaking from the vent point is that the oil is being overheated to the point of "flowing", or being forced out, of the vent point due to the pressure of expansion from heating.

And now the PTO/PTU does not get sufficient cooling and begins to fail.

Hmmm...looks as if I should have read/looked at the linked TSB first.