Went from a 2020 F150 with 2.7L eco to a 2024 F250 with 7.3L and something has been bothering me. I notice the 7.3L experiences engine braking at any RPM whereas the 2.7L would coast/accelerate very similar to neutral until about 2000rpm and then you could feel the engine braking come to life. Also if I drive the 7.3L when the engine is still cold and oil temps are below ~100F then it has significantly less engine braking. Lastly I notice on the 7.3L that the engine braking will decrease if I'm towing my 7000lbs trailer down a hill and exceed roughly 2700rpm. It will not entirely cease but I'll lose ~20% of perceived drag. Upshifting to a higher gear to get below 2700rpm can sometimes be as effectual at engine braking than downshifting from 3000rpm to 3500rpm.

All of the above together, it seems the computer on my F250 likes to close the throttle valve at any engine rpm when not touching the pedal and this retards speed always. It doesn't do this, or does it less, when the engine is cold or when under a high load scenario and rpms climb beyond 2700, the latter perhaps to keep the vacuum pressure from exceeding some sort of limit. Comparatively the computer on my F150 with 2.7L eco seemed to not close the throttle valve until higher in the rpms, roughtly around 2000 where it comes on strong and consistently gets stronger all the way to 5000rpm.

For daily driving I prefer the engine braking experience of driving my F250 cold and my old F150, I don't like the experience driving the F250 warm. In many scenarios I have to feather the pedal where otherwise a normal car or my F150 would coast. And I have to imagine this constant engine braking is taking away 1-2 mpg in mixed or city driving. Eco mode and normal mode behave the same here. Because Eco mode is no different I have to imagine that there must be a valid reason to have this engine braking at all rpms but I don't have any technical insight of why.

I have a OBD2 reader for realtime telemetry I used to use with my F150. If there is a throttle valve readout on the F250 I could take a look at that to see how it behaves. If this is some programming choice from Ford then I wonder if a tune could change this to better optimize for mpg. I'd like to have a driving mode setting that did this.

 

The big thing I noticed with the variable engine braking is that anytime the coolant temp dips below 150F, the engine will disable engine braking and coast with fueling (which brings the temp back up to over 150). I drive 16 miles downhill from my home to town, and the truck will frequently go in and out of engine braking, as the temp goes above 150F, drops into the 140's, then comes back up into the 150's after it coasts with fueling.

 

So you think it's adding fuel and spark when coasting and cold? Is that what's reducing the perceived drag or is it from opening the intake and exhaust valves to reduce vacuum pressure?

 

Yes, fuel. These are simple pushrod engines, there's nothing hi-tech in the valvetrain other than the cam phaser. Engine braking happens because fuel is cut, which means no combustion to keep the engine up to temp. For me anyway, that's the reason it will go in and out of engine braking.

 

I haven't ever had problems manually downshifting to stay at any desired speed on any sized downhill with the 7.3L 3.73 gears or 4.30s. Having 4.30 gears will slow you down more when you let off the gas coasting on flat ground.

 

Here's an experience I repeatedly see when driving unladen. I have a road with ~150' of elevation drop over a ~half-mile and a posted 35mph speed limit. As I approach I'll coast and shift to M typically starting in M7 and ~1200rpm. Then I reduce to M3 as the hill begins in earnest. At no time am I touching the brake pedal. At the start of M3 I'll be doing 30mph and 2400rpm and begin to accelerate slowly. Around 60% of the way down I'm at 2700rpm and 34mph. Right around here I can feel it brake less and I'll suddenly find myself at 40mph after the remaining 40% of the hill. Meanwhile, if I upshift to M4 at 34mph I'll drop to 2300rpm and only be going 36-37mph by the bottom of the hill. I run this hill almost daily so I've done this a hundred times and it always works out this way.

Now if I were to downshift to M2 at the 34mph mark I guarantee I'd start decellerating, no question about that. But M4 at <2700rpm beats M3 at >2700rpm on this particular hill.

 

It probably has to do with what the torque converter is doing in each gear

 

I agree. Its very noticeable when the torque converter switches between unlocked and locked. 6.2, 6.8, 7.3, 6R100, 6R140, 10R100, 10R140, they all run away a bit when the converter locks up if you're not already at a higher rpm, especially with a load behind them.

 

Just read about torque converters, fluid coupling, slip, and lockup clutches. This really jives with my engine braking experience and now it makes sense. So less braking when cold due to fueling to warm the engine, and less braking at higher rpm due to torque converter locking up. Ford is not programming these trucks with unnecessary amounts of engine braking, it is all normal. Thanks.

 

Interesting discussion! I learned something.

 

Run my truck in manual mode most of the time towing and downshift more fluidly than the computer can.
Engine braking often sees above 4k rpms in the mountains and not had a single issue.
MPG ? Haven't looked in awhile.