MCI8 air issues

[GI-Jane]

Hello.  Complete bus novice, here.  I have had this MCI8 for 5 years.  Other than firing it up 3 or 4 times a year, it has been parked, waiting for me to start my bus project.  I started it up this week, and have 2 new problems.  1) the throttle is limp; just idles. 2) zero air pressure on dash gauge and she won't stand up.  I knew of the quick-release/schrader-type connectors on the air compressor, so I changed them over to quick connects that match my air compressor and attempted to air up the system.  (bus engine off)  It would not take any air.  My compressor stayed full at 90 lbs. 

I am not a mechanic.  I have access to a truck mechanic who has offered to help me.  Can you point me in the direction I should be looking?    Thanks.  Kirt

(OEM 2 cylinder air compressor on passenger side of Detroit)

[gumpy]

Hmmm, are you sure you're looking at the right compressor?  The air compressor is a single cylinder device, and there are no "schrader" valves on it. Yes, it's on the passenger side, but it's mounted on the back side of the engine. Are you looking at the large compressor in the right rear corner of the engine compartment which is driven by a couple belts off the crankshaft? That would be the air conditioning compressor. 

There is a drain line where the tag axle valves are located in the right rear engine access door, on the tax axle fender. This is where you want to attach shop air.

[GI-Jane]

Oh, great.  Wrong compressor.  Regroup and retry, tomorrow am.  Thank you.

[brmax]

A photo if you can, and it may need resized to below 150. Had me wondering on the schrader valves, like whaa, maybe someone tried putting some on the gov.
Anyway as Craig said probably do the r&r on them schraders n couplings and look for the air drain line at right rear access door. Probable hand valve on the connection.

Floyd

[GI-Jane]

Okay, now that I have given my best effort at the Bus Darwin awards for this year, lets get serious.  I open the passenger side rear access door.  Mounted to my immediate right are two valves with an air fill valve between them.  The decal on the inside of the door identifies them as the Rt. and Lft tag axle air valves.  Mounted lower, and bolted to the tag axle fender is another air line that is plumbed to the ground and a decal that says "drain daily".  I took a photo but can't figure out how to attach to this reply.  My goal is to air the system up with whatever method I can, in order to move the bus about 100 yards. (new parking spot)   

[GI-Jane]

I will attach my air compressor to the drain line as per Grumpy's instructions. 

[bevans6]

Good old "drain daily"     That is where I plumbed in an air fill chuck, along with a ball valve to make sure it doesn't leak.

[brmax]

Something you might find is an air leak sound. Some tanks up front have an air pressure relief valve. These typicaly are set lower than many home compressors. Just be aware, its not out the norm. I found on mine the valve to connect to and am sure it finally was made a factory 3 way, with one a drain other had a schrader. I no longer had a clip on air chuck so just put a plain open lincoln style.
Just beware following Gumpy's instruction you may find yourself following his family bus to Alaska or some other great destination 

Good day everone
Floyd

[GI-Jane]

We have had a long hot summer here in Central WA.  Alaska sounds inviting.
Plumbed air through the drain line.  Major air leaking from the area of the top of the 2 front air reservoirs.  I am looking through the manual to see how to gain access to that area.

[GI-Jane]

Can I gain access to the top of the 2 front air tanks by removing the center isle ramp?

[brmax]

Does the gauge on dash build air in any amount close to 100
There may be a drain and air fill/connection point in the compartment access outside below driver, this just for the parking side of the air system.
I think i might look at different jacking options. Rather than removing the ramps floor area and actually not sure if that will give the particular access.
Just wanted to check on if tanks will hold any amount below 120psi.

Floyd

ps: i always like wheel chocks in these situations

[gumpy]

Can I gain access to the top of the 2 front air tanks by removing the center isle ramp?

No.

You'll need to jack it up and block it up and crawl under it. Sounds like maybe one of the tanks is leaking, or, potentially an air beam.

[bevans6]

Easiest way to assess what's happening up front is to jack it, block it, and take one or both front wheels off.  That makes it easy to get in.  Your MC-8 is probably similar to my MC5C.  There would be two air tanks on the rear wall of the front axle bay, passenger side is emergency tank and drivers side is the wet tank.  There would be an air filter and a pressure protection valve mounted on the emergency tank.  There is an air dryer mounted on the front wall of the axle bay.  There are two suspension air beams that are prone to leaking, above the air springs.  You can't get to the air tanks from the inside of the bus at all, there is a major chase-way full of pipes, cables, tubes under the center aisle.  If the air beams are leaking you have to remove the floor above them to try to fix them, but most people simply block off the top of the air springs with plates.  With leaking air beams you need to asses structural integrity - they are what the springs are mounted to, so they hold up the entire bus and need to be strong.  A few pin-holes causing a leak is one thing, major rot would possibly ruin the bus.

[Oonrahnjay]

Hi, Kirt.  Welcome to the craziness.  May I make a "back to basics" suggestion?  The air systems of these buses are complex but once you look at sub-systems, they become much easier to figure out.  Do you have/can you get a chart showing the layout of the system (air compressor, piping, tanks, valves, etc.)?  Such a chart is vital to understanding your system. 
You need to understand what's going on and how the system works to analyze problems.  There are arrangements of pressure valves in the system and you'll need to understand the way that they work to figure out what's wrong.  For instance, there may be a one-way valve on the main brake tank -- the purpose of this would be so that if there is a big failure in some other subsystem, the air in the main tank (used to operate the brakes) will not flow out back out through that valve - it only lets supply air into the tank - and be lost through that leak but will remain in the brake tank so that you can safely maneuver and stop the bus.  If your bus is built like this, and you have pressure in the main brake tank but not in the rest of the system, that would tell you that the compressor is working OK but you have a leak in some other subsystem. If you have no pressure in *either* system, that might indicate a more basic problem -- compressor, governor, air dryer, valves,
etc.  (Note:  this is way over-simplified for example purposes, most recently-built buses have a main air brake tank system, an emergency/secondary brake tank system, and an "accessory" air and tank system; the "emergency/secondary" air brake system interacts with the main air brake system in many ways.)
Also, you *know* that if your bus loses all air while you're rolling down the road (or when stationary), the emergency air system automatically applies and "slams on your brakes", right?

Another thing, some buses have an air accelerator/speed control system (I'm loathe to call them an "air throttle" because there's not really a "throttle" on a diesel).  If there's no air, pressing on the accelerator won't do anything.  Plus, some buses have systems that have air interacting with functions at start-up; with these you might see "lockouts" between regular idle and fast idle, generator/alternator charging not functioning soon after start-up, etc.  If you're seeing a "limp" accelerator at start-up, it very well could be related to your most prominent air problem, or it could be another separate air problem, or it could be a problem that's unrelated to your air system.

BTW, you'll find a wealth of information on this board.  Many people will be happy to help you -- it will be good if you read through the info on the Bendix website to get familiar with general terms and basic systems so you have background when you're asking for help.  Lots of people here have owned buses for decades, others are newer at this.  Especially, you'll want to pay special attention to info from "Gumpy" (Craig), "bevans6" (Brian), "brmax" (Floyd), and "RJ" (RJ) -- they own (or have owned) MCIs near to the model of your bus and they're technically very experienced and savvy.  Others will give you good info, too; they may be experienced bus/truck mechanics, pro drivers, long-time owners of other models of buses, etc.
One thing that will help you a lot is if you set up a photo account.  I had been using "photobucket" but they're been getting really unreliable lately (charging fees, etc. -- "f*" that!) so you probably want to try something else.  You upload a photo to your photo account then you can copy an IMG link.  Paste that IMG link and describe your question -- you'll get good feedback fast.

Sorry to not be a lot of direct help, but you're in the position where you are fighting the very bottom of a learning curve.  Just hang on and learn your way up.  BH,  North Carolina

("f*" that -- forget that!)

[lvmci]

Hi Kirt, just last month my MCI wouldnt hold air on startup. Gary from B&B told me to race the engine and hold it at a high rpm. It worked, but didn't fix the problem. I had wiggled the two release valves on the tanks between the front wheels, previously described and they reseated. These pull valves release water and air daily from the air systems, to keep the air system from rusting and other problems. My 120lb release had become a long hiss releaseing air, so I knew a problem was developing. Those two tank valves were supposed to have cable pulls to make it easy to rid the tanks of water that would spray out as a mist. upon closer inspection the bendix filter was in bad shape also. The updated filter and two release valves are in place, rust was the culprit, the valves would not close intermittently causing the leak, keep g them from closing, Gary's emergency fix pushed the system to force it closed with high pressure. The valves and cables aren't expensive and you can probably replace them yourself, if not rusted in place. You should get a maintainece and parts books or CD. Hope this helps, lvmci...