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Posts: 1088 		Direct Link To This Post Topic: Time for Camping?
    Posted: 20 Jun 2020 at 12:18pm
Our tow vehicle is a 2012 Ford Expedition EL. It has engine braking when in the “Tow-Haul” mode . when you touch the brake pedal, the transmission sets that speed as the max level and will downshift as necessary o maintain the set speed. I just checked our owner’s manual to be sure. It says that engine braking is available in all forward gears when the transmission is in overdrive and tow/haul selected.
We use this feature Always when towing.
Vann

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Posts: 1088 		Direct Link To This Post Posted: 20 Jun 2020 at 12:17pm
Our tow vehicle is a 2012 Ford Expedition EL. It has engine braking when in the “Tow-Haul” mode . when you touch the brake pedal, the transmission sets that speed as the max level and will downshift as necessary o maintain the set speed. I just checked our owner’s manual to be sure. It says that engine braking is available in all forward gears when the transmission is in overdrive and tow/haul selected.
We use this feature Always when towing.
Vann

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Posts: 2710 		Direct Link To This Post Posted: 20 Jun 2020 at 9:13am
Originally posted by podwerkz

Originally posted by GlueGuy

The 2.7L can provide the power of a 5+ liter V8, but does not have anywhere near the same compression braking. 

Which would be fine in a car or SUV, but that would be a problem for me if I were buying a pickup (with either size of ecoboost engine) and intending to pull trailers. I think Ford should engineer and include some type of active or passive engine braking system, at least when in 'tow/haul mode'.

To me, it's a safety item. You would likely not be convinced of this unless you have pulled trailers over the Rockies...which I have.

Just sayin.
When we put ours in tow/haul mode (push button), the transmission becomes very aggressive with down shifting on the downhills. More aggressive than I would do, but theoretically the "program" knows what the limits are. The engine remains well below red line, but it is kind of startling the first time it happens.
bp
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Posts: 5290 		Direct Link To This Post Posted: 19 Jun 2020 at 8:37pm
Originally posted by podwerkz

Yep I know how the big diesel engines achieve engine braking, but I do not know if turbo gasoline engines like the ecoboost have a throttle plate that can restrict air intake..(maybe they are supercharged rather than turbocharged?).....but you are saying they do. Ok, I concede that, since I dont know, I've never owned one or worked on one, nor have I googled around trying to figure out if they do.



I only know because I googled "2.7 ecoboost throttle body" and there were some for sale. I kinda figured that no one would add one aftermarket Tongue.  Glueguy looks like he knows what's what on those engines. 

Supposedly there are now some spark ignition gas engines that don't have throttles but don't know of any specifically. 

Yeah calling compression braking Jake brakes is kinda like calling facial tissue Kleenex I guess. ...Glad to hear that compression brakes on new trucks are quieter than in the bad old days....

My Prius has a B mode which is the hybrid equivalent of engine braking. When I select that the ICE stays spinning when coasting downhill when it would normally be off. B mode adds engine braking to the battery regen to minimize use of the friction brakes. Once the battery is full the engine rpm goes up noticeably because the engine now has to do all the braking. Its a small engine so doesn't provide a lot of engine braking once the regen is done.  
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Posts: 966 		Direct Link To This Post Posted: 19 Jun 2020 at 8:14pm
Originally posted by GlueGuy

The 2.7L can provide the power of a 5+ liter V8, but does not have anywhere near the same compression braking. 

Which would be fine in a car or SUV, but that would be a problem for me if I were buying a pickup (with either size of ecoboost engine) and intending to pull trailers. I think Ford should engineer and include some type of active or passive engine braking system, at least when in 'tow/haul mode'.

To me, it's a safety item. You would likely not be convinced of this unless you have pulled trailers over the Rockies...which I have.

Just sayin.
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Posts: 6437 		Direct Link To This Post Posted: 19 Jun 2020 at 7:30pm
The compression braking of a 4L NA engine isn't all that great either. That is what I have in the 2010 Frontier we now drive.
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Posts: 2710 		Direct Link To This Post Posted: 19 Jun 2020 at 7:14pm
The latest EcoBoost engines have a throttle plate and two separate fuel injection systems. One set of injectors go to the intake ports, and the second is direct injection into the cylinders. They also have variable valve timing. The compression braking is less effective mainly because EcoBoost engines are much smaller displacement than an "equivalent" NA engine. IOW, the 3.5L EcoBoost provides the power of an engine of roughly twice the displacement (so around 7 liters (not exact, but you get the idea)). However, it will still only be able to compression brake at 3.5L.

I've seen this between the 2.7L EcoBoost and the 3.5L EcoBoost. The 2.7L can provide the power of a 5+ liter V8, but does not have anywhere near the same compression braking. The 3.5L has a noticeably higher compression braking capability.
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Posts: 6437 		Direct Link To This Post Posted: 19 Jun 2020 at 5:42pm
Okay. I do have some experience with turbocharged engines and engine braking. The 2016 Escape had the 2L Ecoboost engine. It does have a throttle plate.
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Posts: 966 		Direct Link To This Post Posted: 19 Jun 2020 at 5:16pm
Yep I know how the big diesel engines achieve engine braking, but I do not know if turbo gasoline engines like the ecoboost have a throttle plate that can restrict air intake..(maybe they are supercharged rather than turbocharged?).....but you are saying they do. Ok, I concede that, since I dont know, I've never owned one or worked on one, nor have I googled around trying to figure out if they do.

But I DO know how large turbo diesels work...and just FYI...'Jake' is a trade name....and 'engine brake' or 'compression braking' or 'engine retarder' are the generic terms...

Another FYI....when referring to OTR class 8 engine braking, or jake braking, they are only loud on un-muffled exhaust systems (open stacks) in other words, modified exhaust, or really old trucks that had open stacks from the factory.

Put another way: modern, recently manufactured, typical class 8 on-highway trucks, especially fleet trucks, (with intact emissions systems) do NOT have loud engine braking. In fact, it can barely be heard...it does make some noise, but it is not LOUD. And it will be even quieter with horizontal exhaust, which is much more common on newer aerodynamic truck-tractors. 

If the factory exhaust is modified: muffler removed, open stacks, whatever, then yes, the engine braking will be LOUD.

But, apologies to the OP and back to the regularly scheduled programming!
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Posts: 5290 		Direct Link To This Post Posted: 19 Jun 2020 at 12:58pm
Originally posted by podwerkz

Hey, my ears were burning!

I'm no expert! In fact, I have to ask, does an eco-boost (turbo gas) engine even HAVE a throttle plate? I assume they use common rail fuel injection or maybe direct injection, I dont know.

But if so, they will have very low compression braking UNLESS the engineers have added some kind of variable valve timing that can close the intake valves during part of the intake stroke...or maybe close the exhaust valves, and shut off fuel, during part of the exhaust stroke...or a simple exhaust brake like most light truck diesel engine provide as an option.

At any rate, they may have some way of providing engine braking...I would hope so with a vehicle intended for towing...

Again, naturally aspirated engines have some 'natural' engine retarding ability, but turbos don't unless there is some extra hardware added. Yes, the transmission is part of the process, but automatic downshifting on a downgrade relies, again, on the engine having some compression braking available.

At any rate, engine braking is part of the entire experience when towing, especially in the mountains. It helps what we call 'towing authority'...where the towing vehicle (the 'power unit' in commercial language) and the driver have complete confidence and control over the trailer (or trailers).

Its a good thing to have, and reduces the incidence of white knuckles, pinched seat upholstery,...or worse!

Wink

Yeah, AFAIK most all spark ignition engines have throttle bodies. The ecoboost engines do and so does my Toyota. Compression ignition engines (eg, diesels), do not. So, they need compression release (aka jake) brakes to do engine braking. Jake brakes open the exhaust valves at the end of the compression stroke to release the pressure in the cylinders so the is no spring back during the exhaust stroke. That's also what makes a semi truck sound like an automatic rifle when the jake brake system is activated. Sine the compression in a diesel is roughly double what it is in a gasser I would think that you could develop about the same engine braking capacity in a diesel with half the displacement per pound as with a gasser.  
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