'01 F250 Super Duty, 2wd.

The vehicle is decelerating when going downhill and towing no load with OD on. It is shifting kind of hard into OD, though. All other gears shift very smooth, (you can barely feel the sifting). I drive with a light foot, too.

Shifting into neutral while going downhill, the vehicle picks up speed at what feels like a normal rate, (I've got a bridge over a river near me that has a pretty good incline where I tested this on).

When driving on a 'normal' surface, (i.e. no drastic incline or decline), I'm either giving it pedal or it's slowing down if I'm going over 40 mph. I can FEEL the vehicle begin to slow as soon as I take my foot off the accelerator above 40 mph.

I've had all wheels off the ground and they're all spinning easily with no noticeable drag. Pulled the drive shaft off the rear end and both wheels spun easily with no unusual noise.

In 1 I get engine braking as well as in 2. When in D, I get no engine braking in 1st - 3rd gears. The engine braking in 1 and 2 feels JUST like it does when I'm in 4th, at 40+ mph.

We replaced the trans solenoid pack PRIOR to replacing a faulty PCM, (which we got through DTC, recommended on these forums).

What is my next step in testing or repair? Is this just how the trans works without a chip/tune? It's really unpleasant to drive at highway speeds and it's killing my mileage.

Could the old faulty PCM have damaged the new solenoid pack?

 

I don't see a problem.

Engine braking in 4th, yes.
No engine braking in 1,2, or 3 when in OD range.
Engine braking in 3rd with OD "OFF" (button pressed on shifter) above 40-45 MPH. Yes.

How is it killing the mileage? The injectors are effectively off when this engine braking is taking place....otherwise your engine would be at idle while slowing down and burning fuel.

If the above scenarios are taking place, your transmission is functioning as the PCM wants it to.

 

if TC isnt locked and you decellerate in 4th, the lock up can be weird feeling when slowing down. The trailer is bumping into the hitch at that point to.

 

It's doing all this with nothing on the vehicle. Just an empty bed and no trailer. This is normal for it to SLOW DOWN coasting downhill? That doesn't seem or feel right.

It's killing my milage because I have no coasting whatsoever, and most of my driving is over 40 mph, so I'm CONSTANTLY on the accelerator.

 

What is your average mpg?

Operation of the truck/transmission seems normal from what I get via posted info. But as you know, not driving it in person can be hard to tell for sure.

Freewheeling down hill and having to use brakes seems much less ideal to me

 

Yes, that's how it is supposed to work.

Again, that is how it is supposed to work.

If the coast clutch is on in fourth gear you'd know it because that would cause the output shaft to STOP TURNING. The rear wheels will be locked.

There is nothing wrong here. There is no further steps to diagnose.

 

I prefer to use TC lockup as much as possible,even driving around empty.Don't want to freewheel in tight corners and love engine braking on steep hills.

 

By an actual torque measurement in the driveshaft torque converter lockup adds about 10% to the engine braking over the engine braking with the torque converter unlocked.

 

By seat of the pants feel, an applied torque converter clutch adds 300,000,000% in 4th and over 5,000,000,000% in 3rd, 2nd, and 1st so long as the coast clutch is applied and working.

 

I'm sure your seat of the pants feel is more accurate than my torque meter in the driveshaft.

 

That's about what my pants report as well. Descending a grade, especially with a heavy trailer, is no fun without the t/c locked and coast clutch doing its thing.

 

It's not just downhill that I noticed the problem, it's even on a flat stretch of road. If I'm going 50mph and let off the accelerator, the vehicle speed slows to 40 within 5 seconds. THIS is what I'm complaining about. If I let it slow to 30-35mph, then accelerate again, it will coast after letting off the pedal as long as I don't get back into 4th gear. We have an 03 Excursion with the 6.0 in it and it doesn't behave this way, and I've never driven any vehicle that did this without something being amiss, so it just seems like something isn't right.

Perhaps I mis-titled the thread. All the searching I've done, the coast clutch topic came up so that's where I got the idea from.

As for my mileage, if I can keep it out of 4th gear I'm around 15-16 mpg. When I have to travel into that speed range, it gets to about 12. My fuel consumption tests have all been over 30-or-so mile runs. I'm not relying on the readout thing on the top of the cabin, either, as I've read they can be unreliable. I've calculated based on my fuel consumption via the fuel gauge and trip odo, (fill an exact number of gallons and watch). I've been trying to figure the issue out over the course of a few weeks now.

A side note on my consumption calculations... I dropped the tank less than 200 miles ago and tested the sending unit, which tested good in several positions so I have to believe it's reporting accurately.

 

Cannot compare to a 6.0 with a 5r110

What gearing and tire size does the vehicle have?

Have you verified the exhaust backpressure valve isnt stuck partially closed? Or that there isnt some rigged up wiring from a previous owner that uses it as an exhaust brake causing it to close under the certain conditions?
Doesnt seem likely to be an ebpv issue by what you described, but nonetheless worth asking.

If I am understanding everything correctly, is that your biggest issue seems to be slowing down when above 40mph in OD, and that everything else seems fine?

 

Engineering humor at its finest. Let's see how many take these remarks seriously and protest vigorously.

 

The tires are 265 70 16

Only other issue is it shifts kind of hard around 45-50 mph. It's not a smooth shift like every other shift point. This doesn't really bother me since I'm such a light-footed driver. I can take it easy on it and the shift is less hard, but still harder than other shifts by a noticeable amount.