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 > RPMs dropping uphill, Ford f-450

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Travel_1234

PA

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Posted: 09/09/20 02:54pm Link  |  Quote  |  Print  |  Notify Moderator

We are experiencing odd vehicle problems and were wondering if anyone has any ideas. When going uphill (~5% grade @2500 ft above sea level), the rpms slowly decline, pedals wide open throttle. Dual cooling fans come on and there is an added noise and slight vibration.
The vehicle is a new to us ford f-450 pickup, 2013, 15k miles, all the tow packages and upgrades. We are towing a triple axle grand design momentum fifth wheel w/ dry weight of 14,500 and gross of 18,500. We have no toys and minimal stuff (first trip). The truck should be able to handle much heavier stuff..it’s about as big as we could go with a pick-up truck.

Thoughts?

theoldwizard1

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Posted: 09/09/20 03:39pm Link  |  Quote  |  Print  |  Notify Moderator

Are you in tow/haul mode ? Did it downshift ?

What was the speed at the bottom and how far did drop ?

BarryG20

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Posted: 09/09/20 03:49pm Link  |  Quote  |  Print  |  Notify Moderator

Not trying to be smart Alec here and not saying there may not be something wrong with the vehicle as there may very well be but hard to say from the minimal description of slight noise and vibration

If that didn't happen every vehicle that tows (or otherwise for that matter) would not have a problem going up hill, hauling a load etc. Those dual cooling fans, expelling heat from the engine and or transmission whether through oil, water or air all take their toll on horsepower (dont get me wrong not implying a lot of horsepower but a couple here or there start to add up).

The work (in regards to physics) required to move a large load uphill is significantly more than on the flat. Even though you say the truck should be able to handle much more you still have a very heavy trailer. Dry weight 14500, loaded light perhaps it is only 15500 maybe more. Not to mention the frontal area of the toy hauler not quite as good as a sail but not far from it. That is going to put a lot of load on that engine 400 hp or not.

You might try downshifting to direct drive and see how it goes (not that familiar with fords so unsure which gear that would be on my ram it would be 4th gear). You may not be flying up at 65 or 70 but you may be able to hold speed and rpms. When in top gear in overdrive or even double overdrive that puts additional stress on the engine and transmission for sure when it starts to struggle and will lose speed and rpms.

Diesels are great but they do have their limitations. The f450 power wise is not any more capable than the 250 or 350 assuming the same engine. 400hp is 400 hp it can only do so much.

How much rpm loss is there, corresponding speed loss how much, the noise when does it start, where does it seem to be coming from, the vibration when does it start, where does it seem to be coming from (engine bay, underneath truck, rear of truck etc), what speed and rpms are we talking about?


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blt2ski

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Posted: 09/09/20 04:03pm Link  |  Quote  |  Print  |  Notify Moderator

Assuming you are around 25,000 lbs total. 100+sq ft of frontal area. You need 150-175 hp to go 60 on a level ground. Another 50-55 hp per 1% grade. You are needing more HP than you have. Yes you should be slowing down some.
Also, I don't believe a 2013 has 400hp. But could be wrong.

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time2roll

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Posted: 09/09/20 04:05pm Link  |  Quote  |  Print  |  Notify Moderator

RPM declines with a decline in speed would be normal. WOT would be subject to some fluctuation in speed. After a downshift the torque converter could be unlocked and you may see a drop in RPM as it locks up again.

What is the rpm at and how much does it decline?


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sch911

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Posted: 09/09/20 04:12pm Link  |  Quote  |  Print  |  Notify Moderator

A 5% grade and the altitude would cause additional load. If your maxed out in high gear you will slow down. Simple physics. Period.


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Lwiddis

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Posted: 09/09/20 04:52pm Link  |  Quote  |  Print  |  Notify Moderator

Were you downshifting? Tow haul engaged?


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Lynnmor

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Posted: 09/09/20 04:55pm Link  |  Quote  |  Print  |  Notify Moderator

The transmission should downshift to keep the rpm in the power range, unless you are playing with the manual shift. If the engine temperature is over a certain value it might be reducing power to protect itself.





BarabooBob

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Posted: 09/09/20 05:08pm Link  |  Quote  |  Print  |  Notify Moderator

Downshift to keep the engine in the power band. You may just have to manually downshift, keep the rpms up, and SLOW DOWN. Even semi's slow down on 5% grades and they have a LOT MORE torque than you do.


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Turtle n Peeps

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Posted: 09/09/20 06:22pm Link  |  Quote  |  Print  |  Notify Moderator

Simple: You ran out of horsepower.


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