I'm not saying it won't go into 10th, what I'm saying is at the same speed, it typically ran at a lower gear with the engine brake on.

 

A Jake brake is a compression brake. A third valve ( usually not the exhaust valve) is opened at or near the top of the compression stroke, which releases the compressed air, then is closed. As the piston goes back down this creates a low pressure area or vacuum in the combustion chamber, which creates a braking force.

An exhaust brake blocks the exhaust flow, forcing the piston to compress air against an obstruction, which creates braking force.

A gas engine creates braking force by having the piston draw in air past a closed throttle blade, creating vacuum and braking force.

 

Great explanation.

I have never seen an extra valve dedicated to an engine brake system though? I am curious what manufacturer uses this method vs the oil activated solenoid for the exhaust valve?

 

Okay, will try and clear up some misconceptions...

The exhaust brake on the PowerStroke, as well as the RAM Cummins, maybe the gm too but I don't know for sure, uses the variable geometry turbo vanes to close off the exhaust flow out of the engine to raise back pressure in the cylinders to achieve braking affect.

An engine brake, aka "Jake Brake" is a compression brake, and there are actuators on top of the valves in the cylinder head to manipulate the valves which basically turns the engine into a big air compressor. When applied the fuel is shut off to the injectors, and the valves open to allow air into the cylinder, then closed before the compression stroke, then the exhaust is opened to release the pressure, that is the loud growling popping noise you hear from the 18 wheelers as they slow down. This is why they are known as an engine brake, and the one on our type trucks are known as an exhaust brake.

There is also an exhaust brake that has a flapper valve place in the exhaust system at the back of the turbo outlet that closes off by way of a actuator solenoid to create the exhaust back pressure, works the same way as the one on our trucks, just that ours uses the vanes in the turbo instead of an outside valve.

 

Wish I could find the pic, just saw it the other day... there was a set on FB for a Big Cam IV. You could see the extra "valve spring" I suspect air actuated, that opened the exhaust valves in the head,.bridged over from above.

 

I always thought they were operated by an electric solenoid, but I'm probably incorrect.

 

I understand. I use tow/haul mode when towing. Mine is in the same gear with or without the exhaust brake on.

Now tow/haul mode changes shift points but I haven’t seen a difference with the exhaust brake.

Looking forward to pulling to 6,000-9,000 feet above sea level next month. Should be beautiful up there. I typically stay in the “under 1,000” feet below sea level. The exhaust brake works great in Appalachians and I’m sure it will do great in the Rockies.

 

It has been years since I drove a truck, just seems like the switches engaged the brake using air. I could certainly be wrong... searching

 

Me too, on modern engines anyway. Not finding much.

 

Sounds like you were viewing the PacBrake system.

I just have never seen a cylinder head with a dedicated valve for only the engine braking feature. Every system ive seen has used the exhaust valve for engine braking function usually through a solenoid piggybacked to the valvetrain.

 

OK, I did find on newer Jacob Brake systems the exhaust valve ( or valves if multiple) is used, not a separate valve. This allows the turbocharger and muffler to mitigate the compression brake noise associated with past systems.

 

My two cents, if your watching the MPG on your display then it may be correct, but then again . . . If your off the throttle, going downhill with the exhaust brake on and your mileage decreases, the engine works a little verses exhaust brake off coasting down the same hill. Try with and without the exhaust brake on and pay attention to your RPM's as well. Throttle off, and even if your RPM's rise a little common sense says your not putting any more fuel into it than at an idle. Can't wrap my head around mileage going down. lol As far as it wanting to use a lower gear with ex. brake on, it might be something in the programming. Seems there was a recall on a re-flash for the transmission not long ago, don't know if this would fix or have anything to do with your issue.
Seek out a very good Ford diesel tech and pick his brain.

 

This was the pic I was looking for. Not current tech, off a old Big Cam IV Cummins. Looks to me like the solenoid on this version is air operated. If you zoom in a little the nipple on the outside looks like an air fitting and not electrical.

 

All engine/jake brakes are engine oil actuated. They use an electronic solenoid to turn the oil on or off to the piston that un seats the exhaust valves.