Won't stay running unless fully aired up.

[lou432]

Hello again folks , as some followed my bringing her home finally thread know . I was having some issues with it settling to one side overnight and not staying running past 30 pounds of air pressure when I try to crank her the following morning.
  I aired her up three times three separate occasions once it is that full 120 pounds she started right up and stayed cranked.
  She's been sitting for 3 weeks, assuming nothing has changed should be able to do the same... until I figure out what the reasoning behind all of this is, my  question is.... should I get air compressor with a higher tank volume/ cfm? or a portable air tank that will fill her up ?  My thoughts were getting adapter for one of my scuba tanks that will hold 3000 pounds plus and I could feel her up a few dozen times need be?
Shooting in the dark here guys any help is appreciated.What I do know..... Figure out why she's leaking air and then figure how the inability for her to stay running is related.
Information I know , she ran like a top for 16 hundred miles. Oil pressure was questionable due to faulty gauges no problems starting her other than when she's air down or leaning . She's been sitting for 3 weeks on relatively level ground maybe a little lower in the rear. And she still would not stay running for more than 30 pounds . Oil dipstick still reads full.
Thanks for reading!

[gumpy]

So, to clarify....

You're saying that it will start with zero air, but will only run till air pressure gets to 30 psi and then it will shut off.

But if you air up to 120 psi from shop air, it will start and continue to run without shutting off.

Is that correct?

[lou432]

That is correct Craig.

[Jriddle]

Check the rear shutoff switch it may be in the off position. What confuses me is the is the fact it will run fully aired up which it shouldn't if the switch is off. I would check that switch first to be sure it is on.

John

[gumpy]

Well, I'm stumped, but I'm going to suggest that as you air it up, try starting it at intervals of 10 psi. I suspect at some point, it will stay running. Probably sooner than 120 psi. Maybe that will give us a clue. The air system does different things at different pressures.

It's a shot in the dark.

I don't believe it's related to the angle of the bus from deflated air bags. I suspect it's related to a pressure device, though I'm not aware of one on the shutdown system that would
cause this kind of behavior.

[Dave5Cs]

Its either a check valve or the air drier if you have an AD2 still. Are you airing it up with the shop compressor in the back or in the front. If it is in the front it will by pass the air drier and it should air up all the way. If you air it up at the back it all goes out at the first opportunity which would be the purge valve on AD. Yes NO
When the engine and its compressor is running it first goes to the AD and will not build if it is opened or the check valve is stuck opened. See if there is a leak about center on the front wall of the front wheel well. Don't go under unless it is blocked up just listen up there.
Dave5Cs

[gumpy]

Its either a check valve or the air drier if you have an AD@ still. Are you airing it up with the shop compressor in the back or in the front. If it is in the front it will by pass the air drier and it should air up all the way. If you air it up at the back it all goes out at the first opportunity which would be the purge valve on AD. Yes NO
When the engine and its compressor is running it first goes to the AD and will not build if it is opened or the check valve is stuck opened. See if there is a leak about center on the front wall of the front wheel well. Don't go under unless it is blocked up just listen up there.
Dave5Cs

The problem is not that it won't air up. 

The problem is that it won't stay running unless the system is aired up first.

If he starts the bus with no air in the system, it will only run until the air builds to 30 psi. Then it shuts off. This initially would lead me to think the rear shutdown stop/run switch is in the stop position, as John mentioned above. However, Lou says that if he airs the system up to 120 psi using shop air before he starts the bus, it will continue to run just fine. This would contradict the stop/run switch being in the stop position.

[Dave5Cs]

I working on where he said there was a leak which I was premature on. Sorry But
I understand that part,LOL I guess I was trying to figure out where he was airing up the system with the shop air so that we might see something in that line that was allowing it to not stop and we know where the air comes from the bus compressor to air up to only 30PSI and then shuts down. These are two different places and one would have nothing to do with the other being the 30 and shut down and the 120 and no shut down because it may be past the shutdown switch. I know I am not making sense but it was that we were putting them both in the same order and it is not.
Dave5Cs

[Dave5Cs]

Craig how about if he take the air fitting off the back of the shut off valve and then start it and see if it build and stays running. If he needs to turn it off just put it back on and pull on and hold the shaft to stop the engine.
Dave

[gumpy]

I think I may have the answer to this. Or at least a plausible theory...

I believe the skinner valve that controls the shutoff cylinder is sticking in the open position.

In order to shut off the bus normally, air is applied to the shutoff valve by cutting the power on the skinner valve which opens and allows air to flow to the shutoff cylinder.
The skinner valve is normally open. It requires power to hold it closed and not activate the shutdown cylinder. The master switch is turned on, power is applied and the
skinner valve closes, which cuts off air to the shutoff cylinder. If it were sticky, it may not close when power is applied until enough pressure builds up to force it open.
As pressure builds to 30 psi, with the valve still not closed, the shutdown cylinder is activated. This is the symptoms of the stop/run switch being in the stop position.

By pressurizing the system first, there is higher pressure on the valve, which helps overcome the stickiness and pushes it closed when power is applied. 


Ok, shoot holes in the theory.

[gumpy]

Craig how about if he take the air fitting off the back of the shut valve and then start it and see if it build and stays running. If he needs to turn it off just put it back on and pull on and hold the shaft to stop the engine.
Dave

He could do that. Might have to plug it some or it might not build air.

This might also help validate my above theory. If the air is plowing out the supply tube as it airs up, and then stops as pressure builds up somewhere past 30 psi, it would indicate
the skinner valve is indeed sticking.

[buswarrior]

Quick and dirty, let's eliminate the symptom, then work on the cause?

Remove the two screws on the engine shut down piston, and let it hang away from the stop lever.

Start bus, and observe the behaviour of the piston.

Who has a picture to help point out the thing to remove?

If theories about sticky stuff are correct, the piston will poke out as pressure builds, and then retract when whatever unsticks?

First, let's get the bus engine running consistently, then we'll try trouble shooting?

happy coaching!
buswarrior

[lou432]

Wow! It feels like I just went to a meeting with engineers, and not the kind that drivetrain is LOL!
  But I do comprehend the theorys you all speak of .
  I will not be back in New Hampshire till as early as early as this coming Saturday morning but may not be back until the following weekend.
  Just to confirm I did check the rear shut off switch As I accidentally hit it on my trip and when I went to start her back up there was no engaging sounds of the starter.
  And yes I'm a big fan of pictures because I wouldn't even know where to start!
I am airing it up from the front of the bus does have a what I believe is a check valve off and on before the nipple
  Breif  Point,the compressor that I have I have to stop the flow of air when it balances out from the compressor to the bus then let the pressure build up well past 120 pounds on the compressor and then release more air. Have to do this multiple times to get it up to at least a hundred or so. What are other better options? A bigger compressor that I would want to haul around with me just in case :-) or a large cylinder of compressed air that would not rely on electricity to run. Just need to keep that question alive in the thread.
    Thanks again Gents! Keeps me in the know and nothing like being educated!

[Scott & Heather]

To clarify, if you have a shutdown lever that's air operated (and I think you do) it won't stop the starter from turning. It merely stops fuel...so what you're talking about is the rear engine start switch, what everyone else here is talking about isn't a switch, it's an actual mini air piston that pushes a lever to shut your engine down. Here's a pic of one:




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[gumpy]

BW is right on his idea of confirmation. You can loosen the screws on the shutoff cylinder, remove one and twist it away from the shutoff lever and try running
the engine up to full air, while watching the cylinder behavior.


As for shop air input, the best location is typically in the right rear engine access door. There's usually an air drain there with a quarter turn valve. You can add a male
air fitting to the drain line and just chuck your compressor in there. You should be able to run the compressor from 0 up until 120 psi. At that point, the air dryer
will blow off and will continue to blow air until you shut off the quarter turn valve where the compressor is connected.

Here's some photos of the engine stop cylinder: