tow/haul mode working?
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tow/haul mode working?
'05 f250 PS -
Never been sure the tow/haul mode is working correctly - how should the truck performance in tow/haul perform compared to being shifted into low(L) without being in tow/haul with load going downhill - have had other owners tell me how well theirs hold back in tow/haul and not sure mine is doing so well - Thanks
Never been sure the tow/haul mode is working correctly - how should the truck performance in tow/haul perform compared to being shifted into low(L) without being in tow/haul with load going downhill - have had other owners tell me how well theirs hold back in tow/haul and not sure mine is doing so well - Thanks
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From: Stephensville WI
If you're in Tow/Haul mode and you have to jump on the brakes, you will feel the truck downshift aggresively to help slow you down.
When going down a grade in Tow/Haul mode, if you use your brakes to slow down the truck will downshift to help you hold your speed.
When accelerating, you will notice the truck seems to stay in the lower gears a little longer.
From the Owner's Manual:
Tow/Haul delays upshifts to reduce frequency of transmission shifting.
Tow/Haul also provides engine braking in all forward gears when the
transmission is in the D (Overdrive) position; this engine braking will
slow the vehicle and assist the driver in controlling the vehicle when
descending a grade. Depending on driving conditions and load
conditions, the transmission may downshift, slow the vehicle and control
the vehicle speed when descending a hill, without the accelerator pedal
being pressed. The amount of downshift braking provided will vary based
upon the amount the brake pedal is depressed.
When going down a grade in Tow/Haul mode, if you use your brakes to slow down the truck will downshift to help you hold your speed.
When accelerating, you will notice the truck seems to stay in the lower gears a little longer.
From the Owner's Manual:
Tow/Haul delays upshifts to reduce frequency of transmission shifting.
Tow/Haul also provides engine braking in all forward gears when the
transmission is in the D (Overdrive) position; this engine braking will
slow the vehicle and assist the driver in controlling the vehicle when
descending a grade. Depending on driving conditions and load
conditions, the transmission may downshift, slow the vehicle and control
the vehicle speed when descending a hill, without the accelerator pedal
being pressed. The amount of downshift braking provided will vary based
upon the amount the brake pedal is depressed.
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The truck is shifting down and holding in gear as described in the owner's manual - what I'm curious about is the "engine braking" - is it merely being in a lower gear (as manually shfted into L) or is there additional braking provided by the tow/haul mode - should I expect the truck to hold back better in tow/haul mode than it does when placed in L and not in tow/haul mode?
Hotshot
Joined: Aug 2006
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From: Whittier, CA
The engine downshift braking won't be nearly as effective with the 5.4 motor as with the PSD. Some of the dramatic posts you read are probably by those with the diesel. I had the 5.4 in the F150, didn't have tow/haul mode of course, but manually downshifting was helpful, not dramatic.
Bill
Bill
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From: Stephensville WI
Funny, but I've always heard it was just the opposite, gas engines are better for compression braking versus diesel engines. This is one main reason the big rigs have "jake brakes", to compensate for the lack of compression braking of a diesel engine.
Hotshot
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From: Whittier, CA
I've always heard just the opposite, and now that I own one the experience proves it out. It's just a matter of compression ratio.
Bill
Bill
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From: Stephensville WI
Here, this discusses what I am talking about:
http://www.tecbrake.net/theory.htm
Cut from about 1/2 way down the page.
In normal operation, a diesel engine provides power through compression of air in a cylinder into which diesel fuel is injected and ignited. When fuel is cut off by releasing the throttle, the engine produces no power. It does, however, continue to compress air during the compression stroke of the piston. The "work" required to compress this air is obtained from the inertia of the vehicle. Upon reaching the top of the compression stroke, compressed air forces the piston down, canceling out all of the "work" performed on the upward stroke. The result is that power is returned to the vehicle via the crankshaft during the expansion stroke. The only retardation offered by an engine without an engine brake is friction from the moving parts.
http://www.tecbrake.net/theory.htm
Cut from about 1/2 way down the page.
In normal operation, a diesel engine provides power through compression of air in a cylinder into which diesel fuel is injected and ignited. When fuel is cut off by releasing the throttle, the engine produces no power. It does, however, continue to compress air during the compression stroke of the piston. The "work" required to compress this air is obtained from the inertia of the vehicle. Upon reaching the top of the compression stroke, compressed air forces the piston down, canceling out all of the "work" performed on the upward stroke. The result is that power is returned to the vehicle via the crankshaft during the expansion stroke. The only retardation offered by an engine without an engine brake is friction from the moving parts.
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From: Stephensville WI
I always thought this was Diesel Theory 101, but I'll explain firther:
On a gasoline engine, when the throttle is closed, the piston pulls against the closed throttle plate when the intake valve is open. This creates a vacuum. The force needed to pull the piston down and create this vacuum is what you feel when you take your foot off of the throttle or shift down to slow your vehicle.
On a diesel engine, you don't have these forces working for you because there isn't a throttle plate. There is no restriction for the piston to pull against on the intake stroke (no throttle plate) so it draws in air freely. It requires force to compress this air on the compression stroke, but that force used is regained when the comressed air pushes the piston back down on the power stroke.
On a gasoline engine, when the throttle is closed, the piston pulls against the closed throttle plate when the intake valve is open. This creates a vacuum. The force needed to pull the piston down and create this vacuum is what you feel when you take your foot off of the throttle or shift down to slow your vehicle.
On a diesel engine, you don't have these forces working for you because there isn't a throttle plate. There is no restriction for the piston to pull against on the intake stroke (no throttle plate) so it draws in air freely. It requires force to compress this air on the compression stroke, but that force used is regained when the comressed air pushes the piston back down on the power stroke.
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From: Whittier, CA
http://dodgeram.org/ki4cy/exhbrake/exh_brake.htm
This supports what you say. The compression braking is less on the diesel. Basically because there is no vacuum. The compression on the diesel is offset by the decompression on the down stroke. I stand corrected so far as theory.
Still, my PSD is much better at holding speed downhill than my 5.4 could ever hope to be. In fact, my old 1988 5.0 was better at maintaining a downhill speed than the 5.4. Even though the front diff on the '04 F150 did not disconnect the hubs. That model only disconnects in the TC. I can only guess that it's the extra rotating mass in the PSD. Maybe the turbo exhaust restriction plays a part too. The 5.4 was in a lighter F150, and a 4 speed trans.
I know this, going down a certain hill in Big Pine CA in the 5.4L required a lot of brake while the same hill and same trailer in the PSD requires almost none even though the truck weighs about 1k more. Touch the brake to force a downshift and just sit back and slog along.
Thanks for your input, Bill.
This supports what you say. The compression braking is less on the diesel. Basically because there is no vacuum. The compression on the diesel is offset by the decompression on the down stroke. I stand corrected so far as theory.
Still, my PSD is much better at holding speed downhill than my 5.4 could ever hope to be. In fact, my old 1988 5.0 was better at maintaining a downhill speed than the 5.4. Even though the front diff on the '04 F150 did not disconnect the hubs. That model only disconnects in the TC. I can only guess that it's the extra rotating mass in the PSD. Maybe the turbo exhaust restriction plays a part too. The 5.4 was in a lighter F150, and a 4 speed trans.
I know this, going down a certain hill in Big Pine CA in the 5.4L required a lot of brake while the same hill and same trailer in the PSD requires almost none even though the truck weighs about 1k more. Touch the brake to force a downshift and just sit back and slog along.
Thanks for your input, Bill.
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Originally Posted by bpounds
I know this, going down a certain hill in Big Pine CA in the 5.4L required a lot of brake while the same hill and same trailer in the PSD requires almost none even though the truck weighs about 1k more. Touch the brake to force a downshift and just sit back and slog along.
Anyway...
--
If you are not loaded, going downhill in tow/haul, and the truck is slowing down fast enough for the computer, it won't downshift.
If you have a trailer or a load in the bed and the truck doesn't slow down fast enough, it'll downshift to hold the speed.
Last edited by krewat; Sep 20, 2007 at 03:00 PM.
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From: Millersville, MD
I just made a X-country tour this summer with my PSD/30' 5th wheel and never once wished that I had installed an expensive "jake brake" ! The tow/haul feature in the PSD is great. I came down some mighty steep mountain passes too...I was duely impressed by the feature....In fact, it slowed the rig down so much on some passes that I had to hit the go pedal more than once!
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Hi Guys,
I have an 05 V-10 with the tow/haul mode. I don't notice a huge difference when I don't have a trailer hooked up, HOWEVER, when I pull my horses in tow/haul mode, the difference is unreal. In all cases I really don't need much brake. On huge downhills I just sit back and enjoy the ride. Compared to other 1 ton trucks I have owned, the the ford tow/haul mode in conjunction with the factory trailer brake system is the best, bar none. If you are new to this system, it is NOT like GM or Dodge where the tranny goes from Overdrive to reguar drive. The Ford changes internal pressures on the fly. You need to drive one to experience the difference.
I have an 05 V-10 with the tow/haul mode. I don't notice a huge difference when I don't have a trailer hooked up, HOWEVER, when I pull my horses in tow/haul mode, the difference is unreal. In all cases I really don't need much brake. On huge downhills I just sit back and enjoy the ride. Compared to other 1 ton trucks I have owned, the the ford tow/haul mode in conjunction with the factory trailer brake system is the best, bar none. If you are new to this system, it is NOT like GM or Dodge where the tranny goes from Overdrive to reguar drive. The Ford changes internal pressures on the fly. You need to drive one to experience the difference.
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That's the kind of report I've been getting from friends with the same set up while my '05 F250 PSD doesn't hold back like that - I've got to constantly hit the brakes to keep speed down after starting down the slope in tow/haul mode - I've tried starting from a dead stop in tow/haul mode (the theory being that I'm in the lowest gear and tow/haul will keep me there) - I tried the same slope with a like load and manually shifted in L (out of tow/haul mode) again from a dead stop and no difference - therefore my original question - What is not working that I'm not getting the kind of holding back that I'm hearing about others getting?
Hotshot
Joined: Aug 2006
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From: Whittier, CA
Barnestormer, I don't know where I got the idea you had the 5.4L. You clearly stated you had a PSD. Sorry about that bud.
Maybe you should give us some stats on your trailer. How heavy? What kind of hills? When you push the tow/haul button do you get a display on the console? My motor braking is very distinct, touching the brake causes the downshift, and you feel it for sure. Do you notice any difference at all when going to tow/haul?
Bill
Maybe you should give us some stats on your trailer. How heavy? What kind of hills? When you push the tow/haul button do you get a display on the console? My motor braking is very distinct, touching the brake causes the downshift, and you feel it for sure. Do you notice any difference at all when going to tow/haul?
Bill