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Topic: Quick air pressure drops while driving (Read 1283 times) previous topic - next topic

Quick air pressure drops while driving

While driving my coach back from Q yesterday I started getting intermittent "dings" from the dash and the "Level System" light would turn on. About 2-3 seconds after that, the front air pressure gauge would dip to exactly 80 for a couple seconds and then go right back to ~95ish. It probably did it every 15 minutes or so.

My first assumption was a leaky bag but the fact that it ALWAYS dropped to the same pressure and then quickly went back up has me wondering if it could be a ride height valve. Thoughts?

I have bubble solution and a spray bottle but haven't yet had my safety blocks trimmed down the inch or so that they need so I can really only troubleshoot from the wheel well.

Re: Quick air pressure drops while driving

Reply #1 –
That is when your air compressor governor is kicking in. The leak can be anything.

Re: Quick air pressure drops while driving

Reply #2 –
Quote from: craneman –
That is when your air compressor governor is kicking in. The leak can be anything.
Can you expand on how that functions please? Is the governor seeing low pressure and thereby telling the compressor to provide more air to that tank?

Re: Quick air pressure drops while driving

Reply #3 –
The governor on the compressor usually is set for 90 psi cut in and 120 psi cut out pressure. If it is getting below 90 it starts building pressure. Not sure why it stops building pressure at 95 on yours. Maybe something else is going on that explains why. Wait for others to chime in.

Re: Quick air pressure drops while driving

Reply #4 –
Elliott I recently replaced both my air pressure transmitters do to erratic indications. One was the primary concern and figured they were both the same age and cycles so proactively changing both was okay for me. Summit racing had the best price and from ordering to having in hand was under 24 hours. Couldn't believe how fast it was.
Scott
https://www.summitracing.com/parts/sww-82894
57$ each

Re: Quick air pressure drops while driving

Reply #5 –
What is your rear air pressure doing? 

My engine air compressor is on at 90 psi, Air pressure never gets below that while engine is on.  And it goes up to about 115 to 120.  The level system dash light is a catch all for any air system/level system/slide system problem.  If my service tank air pressure is low the level system light will be on when I start the coach until about 70 psi.

If it is an air bag you will probably be able to hear it with the engine off.

You have an electronic box in the dash that supplies the reference voltage to the pressure transducers and reads the return voltage and drives the dash gauges. It is not a direct connection and there are multiple possible failure points.  It may or may not be a transducer.  Both of my electronic air gauges failed, something in the box, actually, and the boxes are reportedly unrepairable and unavailable) they have been replaced with mechanical gauges with an air line to the tanks.  A bonus is that you get to see what the tnk pressure is anytime, ignition on or not.

Re: Quick air pressure drops while driving

Reply #6 –
Quote from: Roger & Susan in Home2 –
What is your rear air pressure doing? 
I did see the rear gauge behave the same way once and then after that, it was all the front gauge. I got out and sprayed all my bags today and the rear most bag on each side (behind drive wheels) has an internal leak (see video) but the front bags all look good. The attached video is with the engine on, coach in the "up" position, to put the maximum amount of air into the bags that I can. If I spray the same spot after the coach has auto-levelled (engine off) no bubbles on either of the bad bags.

My aux pump kicks on every 3-5 hours at night, which I suspect is a combination of the rear bags leaking and the temps getting progressively colder throughout the night. As it gets colder, the frequency with which the pump kicks on increases.

EDIT: See video here: https://i.imgur.com/Y8MxZkS.mp4

EDIT #2: Also, on a possibly related note, my step cover slides shut on it's own after about 24 hours. The airlines to it must be pressurized some because even though I can push the cover shut by hand, it slides right back out. I can tell there's an opposing force trying to keep it shut. The only way to get it to retract is to turn the engine on.

Re: Quick air pressure drops while driving

Reply #7 –
Quote from: Elliott –
EDIT #2: Also, on a possibly related note, my step cover slides shut on it's own after about 24 hours. The airlines to it must be pressurized some because even though I can push the cover shut by hand, it slides right back out. I can tell there's an opposing force trying to keep it shut. The only way to get it to retract is to turn the engine on.

Elliott,
This is a shuttle valve (Norge  valve) problem. Either you have a piston that is sticking or you are getting an electronic signal error telling it to close.

Mike

Re: Quick air pressure drops while driving

Reply #8 –
So I drove it yesterday for about the same distance and it only came on twice. One time it was definitely tied to a big bump in the road. We came over a bridge with a sizable drop as we were coming off and as soon as that happened the warning light came on followed by a drop to ~80psi in the front tank gauge. It went right back up to normal pressure a few seconds later.

A couple things that were different yesterday:
    • Both gauges indicated we were maintaining pressure around 105 or 110 at most times
    • I had the auxiliary air pump on
    [/list]

    Re: Quick air pressure drops while driving

    Reply #9 –
    Mike, if the shuttle valve you are referring to has to do with opening and closing the step closure and the entrance step, it could also be the air cylinders that open and close both of them.... That's simple to check and also a similar problem I had with air pressure. Only thing different is my compressor continued to run its cycle all too often..... This sort of sounds like a d-2 governor issue.

    Re: Quick air pressure drops while driving

    Reply #10 –
    So today was again different. No drops in pressure visible in the gauges but the dash would randomly ding at me. Again, often when I hit a big bump or slowed down quickly. Unlike the previous times however, it would keep dinging at me instead of just one ding. It would quit after 10 seconds or so. Is there a comprehensive list anywhere of all the things that could cause that dash light to come on?

    Re: Quick air pressure drops while driving

    Reply #11 –
    A room in our pin lock sensor can cause the dinger.

    Water in fuel.

    Engine ecm faults.

    TV antennae up.

    Brake Air pressure low.

    Rich

    Re: Quick air pressure drops while driving

    Reply #12 –
    Quote from: Rich Bowman –
    TV antennae up.
    This has only started happening with this much frequency since I picked the rig up after getting solar installed. Guess what the installer did? He removed the TV antenna and relocated the alarm switch to the base plate.

    Is there a way to properly disconnect that switch/little white box completely so I can rule it out as something sending false positives?

    Re: Quick air pressure drops while driving

    Reply #13 –
    Quote from: Elliott –
    Is there a way to properly disconnect that switch/little white box completely so I can rule it out as something sending false positives?
    If that switch has two wires then it works in one of two ways to activate the alarm.  It either completes a circuit, or it breaks a circuit.  It is easy to test it.  Simply cut the wires at the switch and see what happens when you turn your ignition switch "ON".  If no alarm, then you are good to go.  Cap the wires and tuck them away.  If the antenna alarm goes off, get back up on the roof and connect the two wire ends together.  That should make the alarm stop.

    If that doesn't work....sell the coach.

    Re: Quick air pressure drops while driving

    Reply #14 –
    Well, it's not the TV antenna, that has it's own light on the dash but I disconnected the switch regardless.

    I blocked the coach and crawled around underneath and sprayed everything I could with bubble solution starting from the two tanks and moving out. Other than the two leaky bags in back, I haven't been able to find any other leaks. Anyone else have any other threads I can try pulling on?

    Re: Quick air pressure drops while driving

    Reply #15 –
    Well I found one leak. The piston for the entry steps cover is leaking. I shut it off at the valve behind the steps so we'll see what that does. At the very least I'm hoping it's the reason our air compressor keeps kicking on every few hours.

    I've already found the previous posts for replacing the valve with an electric one so I'll probably go that route eventually

    Re: Quick air pressure drops while driving

    Reply #16 –
    Finally figured this one out with a nudge from Keith Risch. I started working backwards from the front tank in the air system diagram and ultimately started noodling on the D2 governor. I know that those come out of the box already set to a pressure range but Keith suggested I not assume mine hadn't been lowered. So I went ahead and adjusted the cut-out pressure at idle to 115 (previously it had been around 98 or so). BAM, that did it. I just drove three hours over horrible roads and the pressure didn't drop below 105-110 and usually hovered around 120ish.

    I guess as parts of the system downstream from the front tank required air when hitting bumps, it simply didn't have enough when it was hovering around 100-105 and it would instead trigger the protection valve to kick in .

    Re: Quick air pressure drops while driving

    Reply #17 –
    It's always a great feeling when you figure out something like that and get it fixed. Of course something else will pop up again sooner rather than later but now you have that knowledge and you can pass it on to the next guy that needs it.

    Re: Quick air pressure drops while driving

    Reply #18 –
    Quote from: Journey, Roam, Explore –
    Of course something else will pop up again
    Lol yep. I think one can only hope that they spend more time enjoying the coach than they do fixing it and I'm slowly turning the tide in my favor.

    These older coaches are probably nearing a turning point too. They're either going to become too much of a project for anyone to buy or become one of the last few good specimens of a dying breed. There's a certain amount of satisfaction knowing you're pushing it towards the latter.
     

    Re: Quick air pressure drops while driving

    Reply #19 –
    Too much of a project.... not.
     Respectfully, with the vast amount electronically, unserviceable power plants coming our way and here already ..    I'll keep my mechanical 8.3 until the parts disappear.

     Or today's mechanics can't figure it out, which will prolly come first.    Just sayin.