Who Knows MCI Air Systems

fredcliff · January 28, 2011, 12:01:40 PM

We have a issue with our air system won't build air and shuts down our Motor any idea's?

bevans6 · January 28, 2011, 12:24:34 PM

Throw us a bone, dude!

what bus, what year, what engine, how long does it run before it shuts down, is it making obnoxious noises, is it cold out, could the air lines to the air dryer be frozen, did it just happen, did it work right last time, and a dozen other things I can't think of...

wildbob24 · January 28, 2011, 01:38:14 PM

I believe he has an '84 MC9 with a 6v92 in it.

Bob

Bruce MC9 · January 28, 2011, 03:35:42 PM

Are you sure it's not building air pressure at all? I had a similar problem with my MC-9. It would start and run until enough air pressure was achieved to operate the shut down of the rack. I found that I had inadvertently left the rear engine shutdown switch in the wrong position. I was embarrassed when I figured out what was going on! I am sure I have many other painful lessons to learn as well!

wildbob24 · January 28, 2011, 04:13:59 PM

Fred,

I agree it must be building some air, since the shutdown needs air pressure operate. As Bruce said, I'd be checking those rear switches.

Bob

robertglines1 · January 28, 2011, 04:24:48 PM

Are you using front start button or rear start button.? if using rear start button the front switch must be in the on position. was your bus a greyhound?

fredcliff · January 28, 2011, 06:25:23 PM

Mine is a 84 MCI M9 the air doesn't build to higher than 60 and the emergency switch shuts things down, further more we discovered today that the front leveler is not working. We are working with Mark at MCI to find and correct the problem so that we can get on the road with the band. This week we missed out and had to send RV to Raleigh. I hope the bus is running before we leave for Dallas on Weds

buswarrior · January 28, 2011, 07:00:42 PM

The suspension will not work properly at that air pressure, so unless you have a better reason, don't be trouble shooting the front leveling valve until there is proper pressure.

The air is leaking out somewhere in larger quantities.

You need to find where the air is going.

What "emergency switch" is activating to shut down the engine? Under what conditions?

Keep feeding us info, we'll get you there!

happy coaching!
buswarrior

johnklink · January 28, 2011, 07:30:17 PM

If it only builds to 60 it could be the air govenor

bevans6 · January 29, 2011, 09:24:34 AM

If it builds to 60 and shuts down, then the normal engine stop lever is being activated by the skinner valve in a completely normal fashion, as far as the air system is concerned. The air supply for the engine stop lever cylinder is supplied by the accessory system and the accessory system doesn't get air until the pressure is over 60 psi and the pressure protection valve allows air past. I'm not saying there isn't some problem with the air system, just that the engine stop lever activating at 60 PSI is normal IF the skinner valve is being told electrically to shut the engine down. I would look for oil pressure sensor, fuel pressure sensor, make sure the front and rear engine run switches are both on, a bad skinner valve, etc.

But all that the engine shutting down at 60 psi indicates is that the engine stop cylinder is working. You have to figure out why the skinner valve is sending air to the cylinder.

Edit: thinking on this more, OP hasn't said he has an air leak, but there may be one if the air pressure is leaking down fast after each shut down. I think the sensors are oil and temp, normally open to run, so disconnecting them will let the engine run, and fuel pressure is hooked into the start circuit, not the run circuit. But I don't have that part of the manual memorized yet... what is the summary of electrical sensors and switches that can make the engine shut down?

Brian

Brian

robertglines1 · January 29, 2011, 09:35:49 AM

try back loading with shop air thru the front air fitting in the compartment below the driver outside lower door should be a fitting to add air to system from out side. sometimes this clears a stuck check valve or free up a little ice or trash in line or valve. noticed your in ice belt could very well be problem. put heat into compartment below driver (lower) and close door as much as you can without doing damage to your cord. the valve to relay air to the secondary system is there. a heat lamp or large light bulb will do the job. the other common place for ice is at the air dryer. Keep us up to date on what you have tried. Bob

robertglines1 · January 29, 2011, 09:49:09 AM

I know you have allot of response here. read all of them and decide what sequence you need to approach. Do wish you well. I know it's frustrating. ck easy first water level in tank ;Does oil pressure build during the short run time?

gumpy · January 29, 2011, 10:13:03 AM

You have a problem in your safety shutdown system. Look at Brian's post. Most of it is correct, other then the fuel pressure sensor.

There was another thread on here regarding the same issue. Search it out.

There are only a handful of things that activate the safety shutdown. Check them in this order: Read run/stop switch in the proper position. Low water sensor if your bus is so equipped. Hot engine sensors (left and right). Low oil pressure sensor. There may have been a low oil level sensor, too, but not sure about that one. My 82 doesn't have one.

Easiest way to troubleshoot the sensors is to disconnect the wire (one at a time). and start the bus. If it gets above 60psi, replace that sensor.