Air throttle leak

Topic: Air throttle leak (Read 1133 times) previous topic - next topic

Air throttle leak

October 26, 2020, 06:57:38 pm

2003 U295--occasionally under "wide open throttle" my throttle pedal will start leaking (hissing sound coming from that area, coupled with dropping air pressure on both dash gauges). If I let up on the pedal, the sound stops and pressure builds quickly. After doing some research on this forum (great resource) it appears that the "treadle valve" needs to be rebuilt on my throttle pedal. It seems like my coach is a bit "new" to still have an air operated throttle, do other coaches of similar vintage (early to mid 2000s) have similar setups?

Re: Air throttle leak

Reply #1 – October 26, 2020, 07:26:44 pm

Quote from: Big Greener – October 26, 2020, 06:57:38 pm

2003 U295--occasionally under "wide open throttle" my throttle pedal will start leaking (hissing sound coming from that area, coupl ...do other coaches of similar vintage (early to mid 2000s) have similar setups?

You have the BEST setup. Air throttle, separate cruise control.

Re: Air throttle leak

Reply #2 – October 26, 2020, 08:45:36 pm

I was not aware of any computerized engines with air throttle.

I don't understand this 2003 U295 model year's throttle configuration.

Re: Air throttle leak

Reply #3 – October 26, 2020, 08:55:02 pm

Quote from: Big Greener – October 26, 2020, 06:57:38 pm

2003 U295--occasionally under "wide open throttle" my throttle pedal will start leaking (hissing sound coming from that area, coupled with dropping air pressure on both dash gauges). If I let up on the pedal, the sound stops and pressure builds quickly. After doing some research on this forum (great resource) it appears that the "treadle valve" needs to be rebuilt on my throttle pedal.

The treadle valve is your braking, which makes sense that your air tanks drop when it leaks. The treadle valve is connected to the brake pedal, not the "foot feed"

Look for mechanical interaction/interference between the pedal linkages (and the treadle valve).

Re: Air throttle leak

Reply #4 – October 26, 2020, 08:59:33 pm

On an 03 the throttle should be through the computer. Maybe someone added it.

Re: Air throttle leak

Reply #5 – October 26, 2020, 10:07:34 pm

If you do have a air throttle, then the thread linked below may be of some interest. It covers my rebuild of the OEM air throttle valve on my coach.

However, since your coach is so much newer, your air throttle may be a completely different setup. If it was added on or converted from electronic throttle after your coach was built, you may need to contact the builder of the kit for rebuild parts and information.

Williams Controls WM453109 Air Throttle Valve

Re: Air throttle leak

Reply #6 – October 27, 2020, 12:13:59 am

Quote from: wolfe10 – October 26, 2020, 07:26:44 pm

You have the BEST setup. Air throttle, separate cruise control.

Bret, what makes this the best combo?

Re: Air throttle leak

Reply #7 – October 27, 2020, 12:17:51 am

Quote from: Michelle – October 26, 2020, 08:55:02 pm

The treadle valve is your braking, which makes sense that your air tanks drop when it leaks. The treadle valve is connected to the brake pedal, not the "foot feed"

Look for mechanical interaction/interference between the pedal linkages (and the treadle valve).

Hmm, I will climb under the coach tomorrow and reinspect, but I'm fairly certain both the brake and throttle pedal have air lines running to/from them. Also, the leak I'm describing only occurs under WOT, not under extended braking.

What year did Foretravel make the switch away from air throttles?

Re: Air throttle leak

Reply #8 – October 27, 2020, 08:42:38 am

Quote from: Big Greener – October 27, 2020, 12:13:59 am

Bret, what makes this the best combo?

Two separate systems. Particularly now that King Control is no longer in business, having just the King Control is less bomb-proof.

Re: Air throttle leak

Reply #9 – October 27, 2020, 08:46:48 am

Quote from: Big Greener – October 27, 2020, 12:17:51 am

What year did Foretravel make the switch away from air throttles?

Good question. The switch happened around the same time they went from pure mechanical engines (like my Cummins C8.3) to electronically controlled engines. But since the different engines used by Foretravel (Cummins, DD, Cat) made that change in different years, determining the exact time of the move from air throttles may be a little murky.

However, there is simple test to tell if your throttle is air or electronically powered:

Use the water drain valve to bleed all the air pressure off your wet tank so the dash pressure gauges read zero. Start your engine. Do you have throttle control as soon as the engine starts? If so, then your throttle is electronically controlled. On my coach under the same conditions, I have to wait until system air pressure builds to about 60-70 psi before my (air) throttle will work.

Re: Air throttle leak

Reply #10 – October 27, 2020, 09:20:55 am

My 2002 ISL engine, which I assume you have also, is definitely an electronically controlled throttle.

Re: Air throttle leak

Reply #11 – October 27, 2020, 09:35:26 am

Quote from: Big Greener – October 27, 2020, 12:17:51 am

Hmm, I will climb under the coach tomorrow and reinspect, but I'm fairly certain both the brake and throttle pedal have air lines running to/from them. Also, the leak I'm describing only occurs under WOT, not under extended braking.

You should have the air schematic in your owner's manual. Our 2003 (albeit ISM) most definitely did not have an air throttle.

Re: Air throttle leak

Reply #12 – October 27, 2020, 07:14:19 pm

Thanks to all for the replies—after doing some more crawling around and referencing parts online, I do have an electronic throttle pedal, from Williams Controls.

The symptoms described in the OP still definitely occur occasionally—any thoughts on the causation, if it's not the throttle pedal?

Thanks,
Ryan

Re: Air throttle leak

Reply #13 – October 27, 2020, 07:26:25 pm

Quote from: Big Greener – October 27, 2020, 07:14:19 pm

Thanks to all for the replies—after doing some more crawling around and referencing parts online, I do have an electronic throttle pedal, from Williams Controls.

The symptoms described in the OP still definitely occur occasionally—any thoughts on the causation, if it's not the throttle pedal?

Can you safely (blocks and chocks) go under the coach and look at the treadle valve and surrounding air lines? Perhaps there is a mechanical interference with one of the lines?

Thinking maybe something like one of the bolts of the throttle pedal rubbing on an air line?

Re: Air throttle leak

Reply #14 – October 29, 2020, 11:27:36 am

BTW, I cannot think of a time that we pressed the throttle fully to the floor, going to Wide Open Throttle (WOT), driving or idling.

Feels to me like a risky way for Cindy & I to drive. Seems like a downshift and lighter throttle would be our way.

Re: Air throttle leak

Reply #15 – October 29, 2020, 04:22:45 pm

How about climbing the continental divide with full tanks, 5 people on board, and pulling a 7,000lbs toad? I was definitely at WOT there...

Re: Air throttle leak

Reply #16 – October 29, 2020, 08:07:16 pm

Quote from: Big Greener – October 29, 2020, 04:22:45 pm

How about climbing the continental divide with full tanks, 5 people on board, and pulling a 7,000lbs toad? I was definitely at WOT there...

Livin on the edge. Reminds me of a game my kids played when they were small, "Willy Go Boom."

Re: Air throttle leak

Reply #17 – October 29, 2020, 10:38:09 pm

Never heard of that game... How else "should" one climb a steep grade...? 1/4 throttle at 15 MPH?

Re: Air throttle leak

Reply #18 – October 29, 2020, 10:49:18 pm

When you are in cruise the cruise will call for full throttle.

Re: Air throttle leak

Reply #19 – October 30, 2020, 08:44:00 am

Quote from: Big Greener – October 29, 2020, 10:38:09 pm

Never heard of that game... How else "should" one climb a steep grade...? 1/4 throttle at 15 MPH?

Actually, the best way to climb a grade is to find a gear and speed where you are JUST under WOT.

Said another way, if you can not accelerate at all by going to WOT, you need a lower gear/lower speed. This is particularly true if engine coolant temperature is rising over spec.

As an example, on Tehachapi/Summit grade east of Bakersfield, CA where it is often ambient temperature quite HOT you will pass overheated vehicles who used WOT, while you are maintaining 200 degrees or less coolant temperature.

Re: Air throttle leak

Reply #20 – October 30, 2020, 01:40:00 pm

It's always been my experience with a diesel that if I can't accelerate ( gain speed ) at 3/4 throttle then full throttle isn't going to help much either. JMHO.

Re: Air throttle leak

Reply #21 – October 30, 2020, 08:13:40 pm

Not only is 'extra' throttle not going to help, it hurts by overheating engine by dumping more fuel than can be used to create more power.

Re: Air throttle leak

Reply #22 – October 31, 2020, 03:15:11 pm

Quote from: wolfe10 – October 30, 2020, 08:44:00 am

Actually, the best way to climb a grade is to find a gear and speed where you are JUST under WOT.

Said another way, if you can not accelerate at all by going to WOT, you need a lower gear/lower speed. This is particularly true if engine coolant temperature is rising over spec.

As an example, on Tehachapi/Summit grade east of Bakersfield, CA where it is often ambient temperature quite HOT you will pass overheated vehicles who used WOT, while you are maintaining 200 degrees or less coolant temperature.

This is exactly how I pull grades. Occasionally though to get around slow trucks I'll go WOT temporarily to make the pass, and then settle back in around 7/8th throttle again. From my experience this will ensure the engine stays in its power band, maintains max cooling, etc. A couple of the above posts seem to infer that using WOT (even briefly) is somehow "bad" and should be avoided. Can you comment on this Brett?

Re: Air throttle leak

Reply #23 – October 31, 2020, 03:20:25 pm

Not Brett but, if you accelerate when you go to WOT all is good. It is when you go to WOT and the speed stays the same you are needing to drop a gear.

Re: Air throttle leak

Reply #24 – October 31, 2020, 05:52:27 pm

Quote from: craneman – October 31, 2020, 03:20:25 pm

Not Brett but, if you accelerate when you go to WOT all is good. It is when you go to WOT and the speed stays the same you are needing to drop a gear.

YUP!

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