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Old 12-05-2021, 11:55 AM   #1
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Auto Exhaust brake function

I think there are many people who don't fully understand how an exhaust brake works and often avoid using the "auto" EB function on the new diesel. Some set cruise control and let the truck do it's thing which is't necessarily a bad way of operating the truck, however, cruise control might not perform as well on a down grade as does the "auto exhaust brake". On the newer trucks many people don't realize that cruise control not only operates the throttle and exhaust brake but will also automatically apply the wheel brakes. For those of us who like to be in charge of when the wheel brakes are being applied using the auto exhaust brake might be a better choice. Here is an explanation on how the exhaust brake works that might help some to make best use of their EB. The amount of braking an exhaust brake can do is a function of the engine rpm x the back pressure ahead of the turbo. There is a maximum pressure that the EB is allowed to generate ... too much back pressure can cause the exhaust valve to float and come in contact with the pistons. The Cummins has stiffer exhaust valve springs than Ford or GM and so its EB is allowed to create 60 psi back pressure. I think the Powerstroke EB will only build about 45 psi back pressure. When the EB is set to auto the speed you are traveling at when you take your foot off the throttle or brake becomes the set speed. If the truck starts accelerating beyond that set point the auto EB will close and back pressure will be generated. If the braking effect produced by that back pressure x the rpm of the engine is sufficient to hold the load back the truck will start to slow, if it slows to a speed less than the set point the auto EB will open allowing the truck to accelerate, thus maintaining the desired speed. If the closed EB does not create enough braking to hold the load back the truck will accelerate increasing the engine rpm and braking effect until an equilibrium can be maintained. Depending on the situation the transmission may automatically drop gears to increase the engine rpm, but there are times when an attentive driver really should lock out the top gears at the top of the hill to avoid having the truck accelerate faster than the rate at which the transmission will respond. If the EB is not able to hold the load back in 6th gear at 55 mph downshifting to 5th, 4th or even 3rd may be necessary (this applies to the 10 speed transmissions ... 4th, 3rd or even 2nd gear might be needed with 6 speed gear boxes). The maximum level of exhaust braking will be obtained at the engine redline. On "auto" mode the Ford will apply the truck's wheel brakes if needed to prevent the engine from revving beyond the engine red line (I suspect Ram and GM would function the same). If you are coming down a grade at 55 mph with the EB set on auto and come up to a vehicle traveling 45 mph you can brake to slow down and the instant you release your foot from the brake a new speed set point is established. (in this situation the EB will close while you are braking to help slow the truck) If you step on the throttle, pull out and pass that slow vehicle, the speed you are traveling at when you release the throttle becomes the new set point.

If you are wanting your EB to slow you down when you release the throttle the Auto mode does next to nothing .... it will help slow the truck while you are braking but as soon as you release the brake it will open because it is trying to maintain speed .... not slow the truck. Full on EB might be the setting you want for slowing your rig down.
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Old 12-05-2021, 12:21 PM   #2
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Nice write up

Might want to include WHICH 'new diesels' you are referring to
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Old 12-05-2021, 02:06 PM   #3
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I use my auto EB almost all of the time.
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Old 12-05-2021, 03:37 PM   #4
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Both of my Rams had 2 settings. Auto was great, the other was too aggressive. I wrote to GMC and told them to go buy a Ram so they would know how one could and should work.
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Old 12-06-2021, 04:08 PM   #5
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Both of my Rams had 2 settings. Auto was great, the other was too aggressive. I wrote to GMC and told them to go buy a Ram so they would know how one could and should work.
LOL I'm sure they knew. I worked as an engineer in a facility that made automotive steering intermediate shafts (including Ram's). We knew all of our competitor's product capabilities. And they knew ours I'm sure.
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Old 12-06-2021, 06:35 PM   #6
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Originally Posted by Old-Biscuit View Post
Nice write up

Might want to include WHICH 'new diesels' you are referring to
That and the service brake only comes with adaptive cruise.

That said, very nice write up.
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Old 12-07-2021, 02:01 PM   #7
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Are you trying to discuss a VGT and the way this can help slow you down or an actual Jake brake?
You have me confused in your write up.
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Old 12-07-2021, 05:00 PM   #8
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I never use the auto EB. I like it that when I can just lift my foot off the gas and the EB is activated. More times than not I just need to slow down a few mph. having to push the brake pedal every time I need to just slow down slightly gets old.
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Old 12-07-2021, 08:54 PM   #9
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Quote:
Originally Posted by jimcumminsw View Post
Are you trying to discuss a VGT and the way this can help slow you down or an actual Jake brake?
You have me confused in your write up.
I'm talking about the factory exhaust brakes used on the diesel pickups (and yes the factory exhaust braking is controlled by the VGT) None of the pickup trucks use a "Jake" brake. If you have a 5.9 Cummins and want more engine braking then what the factory exhaust brake offers you can get an aftermarket "LoadLeash" from Pac Brake. The LoadLeash is still not a compression release brake such as is a Jake, but it offers considerable more braking than the factory exhaust brake does.
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Old 12-09-2021, 06:38 AM   #10
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Originally Posted by Cumminsfan View Post
I never use the auto EB. I like it that when I can just lift my foot off the gas and the EB is activated. More times than not I just need to slow down a few mph. having to push the brake pedal every time I need to just slow down slightly gets old.
On the Ford turning the exhaust brake on (“on” or “auto”) affects the transmission shift points. Because the Ford EB uses less back pressure than the Cummins more rpm is required to do the same level of braking …. I don’t like it. I almost never use the exhaust brake running empty but sometimes use “on” when loaded heavy on flat terrain to help slow down and always use “Auto” on long grades when towing.
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Old 12-09-2021, 02:33 PM   #11
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For my truck which is a 2008 Dodge Mega Cab with the 6.7L Cummins, the exhaust brake is never turned off. It is on 99% of the time upon start-up. Engine is started than exhaust brake is turned on then I am good to go.

The only time T/H is engaged is when I need it when hauling something or towing my 5er.
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Old 12-14-2021, 07:06 AM   #12
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Glad to see this topic addressed. I have been wondering how and when to use it but help from a salesman is almost useless. Finding someone with firsthand knowledge to help me learn what to do and when has been the issue. And using YouTube videos to learn from has its limitations.

I bought my first Diesel back in March as an upgrade to the F150 I had, in order to tow a T/T we were looking at buying. We got a 2021 F250 and I love the crap out of it. Have gone coast to coast 1 1/2 times and found the mountains east of San Diego on I-8/I-10 to be interesting at best. The hills in North Carolina were no better, along with the same in Tennessee. I do not want to ride and wear out my truck brakes in mountainous and hilly areas. Thus having the exhaust brakes is a great feature to have.

I am currently waiting on delivery of a 2022 F350 we ordered back in June (which is finally in production in KY) to tow the 5th Wheel we ended up buying back in September. Once I finally get the F350 I will be able to finally use the EE system to help tow the 5th wheel when we head to our property in TN. Any suggestions for this newbie on what to expect when first engaging the EE? Does it hurt anything if we have it on when not in an area needing it? Can you run it with no trailer attached and not hurt anything? Thanks.
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Old 12-14-2021, 08:56 AM   #13
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Quote:
Originally Posted by Bhidalgo View Post
...Any suggestions for this newbie on what to expect when first engaging the EE? Does it hurt anything if we have it on when not in an area needing it? Can you run it with no trailer attached and not hurt anything? Thanks.
I have a previous gen GM pickup, so my Exhaust Brake system is a bit simpler. On or off. And it's always ON when I'm towing, regardless of the terrain. Same for Tow/Haul mode--always ON. Both systems are listed on my pre-departure checklist.

Note: Given 4x4ord's description of Auto vs On in Post #1, the On setting for Ford appears to align with how the On setting works on my GM.

I never have Tow/Haul mode on when not towing, and only occasionally turn on the Exhaust Brake when not towing if I happen to encounter a lengthy decline that might otherwise require prolonged use of the service brakes.
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Old 12-14-2021, 10:40 AM   #14
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Pro tip
Don't use the EB in the snow or icy conditions.
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