Sitting out in desert in Quartzsite and fired up the bus to head into town after sitting for a few days and I am getting absolutely no response from the air throttle.
Looked through my manuals and I am missing the air diagram page.
The owners manual refers to a manual cable while the parts manual shows the air throttle since I have a turbo.
Where do I start?
Thanks
PS. Air horn also doesn't work which is kind of normal after leak down until its been driven a bit.
Air throttle is typically supplied with air from the same place as the horn. On my bus they're both fed from the auxiliary tank which gets no air until there is 90 psi. If you've been having problems with the horn, perhaps it has totally crapped out - as in the pressure switch which opens the air to the auxiliary tank at 90 psi (or wherever it's set on your bus.)
Disconnect airline at air throttle control unit on the engine then have someone press on the throttle to see if air is coming out first if you get good air at full throttle hook it back up and make sure the control unit isn't leaking if it is you can rebuild it. if not getting air to the control unit it could be a foot valve issue you can do the same make sure you have air going to the throttle and/or foot valve (supply line) and air coming out the control valve. It's a start.
Thanks guys, verified this morning there is no air reaching the engine actuator.
Tackling the foot throttle next; luckily mine is style where the connections are not below the floor.
Does anyone know if there is typically an electrically activated value between the throttle and the upstream air source?
I'm sure you'll find an air supply issue. Those throttles don't just suddenly go bad. Probably a solenoid or air protection valve under driver.
The air needs to reach the foot control from somewhere - follow the line supplying it from the tank. Then check your manual to see what opens the air flow to your auxiliary tank. That may have an answer for you. Even better is if you find a air plumbing diagram.
Quote from: richard5933 on February 03, 2022, 10:41:39 AM
Even better is if you find a air plumbing diagram.
Got a couple versions of the diagram and it doesn't show the air throttle that is on buses with Turbo's.
Kind of hard to trace the lines as it immediately disappears into foam as soon as it goes below the floor.
Prevost support is trying to help but thinking they need to start calling their retired engineers since it is a 1980 bus.
I have verified that it is upstream of the throttle pedal...
Is your air horn still not working? What about your wipers (if they are air operated)?
I'm guessing that you have a failed pressure switch which is not letting air get into the tank feeding the foot pedal. Any way you can check your tanks to see if they all have air pressure? Maybe pulling the drains on them?
Quote from: richard5933 on February 03, 2022, 01:58:24 PM
Is your air horn still not working? What about your wipers (if they are air operated)?
I'm guessing that you have a failed pressure switch which is not letting air get into the tank feeding the foot pedal. Any way you can check your tanks to see if they all have air pressure? Maybe pulling the drains on them?
Hey Richard
Great catch!!! Your right the windshield wipers are also not working...
I will try attacking that tomorrow and see what happens.
Fred
PS. The tank that is supposed to service them does have pressure...
Sounds like you're on the right path at least. Just have to figure out what's keeping the air from getting out of that tank. My money's on a stuck valve.
I would also think there would be check valves that could stick?
There should be a pressure protection valve that holds off air to aux. systems and immediately routes air to brakes till certain pressure 60 or 80 psi or so. Then valve opens and fills aux. system.
Bendix pp2 pressure protection valve.
https://www.jittruckparts.com/bendix-service-valve-pressure-protectio-277148rx
What Chessie said. We replaced our PR-2 valve recently. Not saying that is the problem but should be on your list of suspects!
It might be fun to bipass the bus air system and hook up a small compressor to the gas pedal. Would that get you down the road? Jack
That is a dual air system both fill before the auxiliary do have 120 llbs on the other tanks that valve to the auxiliary doesn't open if under 90 lbs
Quote from: oltrunt on February 04, 2022, 07:57:33 AM
It might be fun to bipass the bus air system and hook up a small compressor to the gas pedal. Would that get you down the road? Jack
Interesting idea would a small tire inflator pump do it? Or hey take the front tire off the ebike LOL!!!
Quote from: freds on February 04, 2022, 08:19:04 AM
Interesting idea would a small tire inflator pump do it?
You'd need one with a built-in pressure cut off switch. Some tire inflators don't automatically stop pumping. Probably would also need at least a small tank so that it doesn't have to cycle every time you pressed the throttle pedal. That pedal is exhausting air every time it moves up.
Hi Everyone
Thank you for your help. In looking at why the windshield wipers are not working I found a line to a pressure regulator off of a manifold port that in the parts manual is supposed to have a plug.
Then working upstream I found an air solenoid valve that wasn't receiving power. A quick jumper wire to the front junction box wiring stud 80 and hey now I have throttle!!!
Now I have an electrical problem to diagnose but that's more in my skill set...
Good find!
An electric solenoid involved in obstructing the filling of a system tank is unorthodox.
Some previous owner had some idea or other... you really want to figure out what he had in mind, and consider re-working to a more traditional pnuematic valve solution, that does not rely on electrcity for coach air system function?
Happy coaching!
Buswarrior
You're talking about a Skinner valve? As in, an electrically operated pneumatic valve?
The value is between the accessory tank and the distribution manifold. That's what threw me off I knew that the tank had pressure...
Not sure of the type, give it juice and it opens.
Check the contacts on the valve... A little corrosion can make things act really wonky. Also check out the grounded side of the valve for corrosion where it gets its ground.
In our 42+ years of same bus ownership we've used a 3000psi scuba tank a few times prior to installing the electric aux. air compressor. One time in the early 80s when our compressor drive failed entering NB NJ turnpike on the south end for Hartford CT @ 3pm on memorial day w/e we quickly bungeed up a scuba tank on one of the engine cradle vertical tubes with the engine door propped open just to get ahead of the rush hour traffic. It was a blast listening to the truckers on the CB radio wondering WTF is that on the back of your bus. LOL We had the fitting we needed to tap the bus air and dropped the tank pressure to 100psi using the 1st stage of the scuba regulator - that would give you enough air for an air throttle for 1000s of miles FWIW...
Been down with Covid for 4 days and just saw this thread. Did you get going? I think I have an air map of mine including air throttle if you think it would help. Can scan it and PM it to you.
Great to be back with the living. Rita and I mask everywhere (but seem to be the only ones), We are doubly stuck and boosted, She had a "cold" for 5 days. Gave it to me on day 5. Just got our home test and I am positive. She is not, but doctor says she had it and gave it to me. Neighbors are calling me Typhoid Teddy. Real nice.....
Hope you are up and running Fred. Let me know if I have any documents you might need.
Hi Everyone
Thanks for the help and problem has been totally solved!!!
The root cause of the failure was more and likely changes that the PO to the last PO made to replace the dash and then never finished the project.
In looking at the wires to the air value they are not factory wiring and looks like they were added as part of the dash project. That and the fact that they are wired to stud 80 which is not used by Prevost. Their recommendation was to wire the valve to stud 20 which is the bus running voltage line.
I am lucky that it decided to stop working while I was parked camping and not rolling down the road.
So in final analysis nothing wrong with the air system and it was an electrical problem.
Quote from: buswarrior on February 04, 2022, 09:57:00 AM
Good find!
An electric solenoid involved in obstructing the filling of a system tank is unorthodox.
Some previous owner had some idea or other... you really want to figure out what he had in mind, and consider re-working to a more traditional pnuematic valve solution, that does not rely on electrcity for coach air system function?
Happy coaching!
Buswarrior
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Prevost loves the Norgren and Humphery valves they are everywhere