Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 09, 2025 ...

Throttle movement before engine response

January 15, 2021, 03:30:17 pm

Hey Y'all, got a question about how much accelerator pedal travel one should have before you get any engine response.
My pedal moves an inch anyway before any rpm increase. How much travel should you see? It is an air throttle and a 3208T Cat.

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Re: Throttle movement before engine response

Reply #1 – January 15, 2021, 03:44:27 pm

I also have an air throttle (and Bendix cruise control), although connected to a Cummins 8.3L.  Same basic setup, I would guess?

If so, take a look at the cable that goes between the air throttle cylinder and the engine throttle lever.  On my '93 model coach, the outer housing of the throttle cable was severely deteriorated from engine heat and vibration.  As a result, the inner cable was not transmitting the full movement of the throttle cylinder piston to the fuel lever.

I rebuilt my throttle cable outer housing to better than new condition.  Afterwards, I picked up almost 10 mph on the top end and also had much better/quicker/more linear throttle response.  See the links below for my old posts on the subject.

Williams Controls WM453109 Air Throttle Valve  (Reply #20, #21 and #22)

air throttle problem

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Re: Throttle movement before engine response

Reply #2 – January 15, 2021, 09:37:10 pm

On my 91GV with a 3208T the air throttle valve is just that.  The accelerator valve is connected  to the throttle valve on the engine via an air line.  The accelerator valve is adjustable, but is difficult to do.  I believe  that the throttle valve on the engine is also adjustable.  Check it out on the engine and that may be where to start.  Have a great day  ----  Fritz

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Re: Throttle movement before engine response

Reply #3 – January 15, 2021, 10:36:01 pm

Have you looked in engine area to see what moves with throttle pedal?  Your coach well be different from others so you will have to look at your throttle lever movements.

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Re: Throttle movement before engine response

Reply #4 – January 15, 2021, 11:43:38 pm

I have already looked at the setup, and mine is air operated. The reason I check with the forum is there is a wealth of knowledge out there, and big truck/bus diesels have not been my wheel house. When it comes to gasoline engines, I am right at home. Therefore, I want to be better grounded before I twist off and rip something apart. Also, "fishing expeditions" could get expensive, and I certainly want to avoid that! I plan to get into it in earnest in the next day or two now that you folk have been so kind to guide me. It is soooo appreciated!!!!!
Thanks again!!!!

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Re: Throttle movement before engine response

Reply #5 – January 16, 2021, 08:38:03 am

But, checking throttle "freeplay" is a 2 minute/2 person job.

With the bed up, air pressure up, engine off have your helper carefully move the throttle, starting with "just barely" until you see the movement at the engine.

As already said, there will be some mechanical linkage between air throttle and engine and that could be the source of your freeplay.

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Re: Throttle movement before engine response

Reply #6 – January 16, 2021, 01:02:51 pm

Yes, Brett, I am aware on how to check it. My questions are to check the "knowledge well" for past repairs that would guide me and save me time that others have already spent on the problems. I plan to post what I have found for future reference also. Also, I search the forum BEFORE I start asking questions and if I see info there, then I don't bother the powers that be. Again, many many thanks to those who are kind enough to point me in the right direction. It is so appreciated!

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