| Author |
Message |
dave spurgeon (206.148.81.177)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, October 21, 2001 - 11:44 pm: | |
Air builds to about 80 lbs at start up, hesitates, then falls back down to about 60. It does this repeatedly (so far for up to 1/2 hour). Finally it will build up to 90, shutting buzzer off and working fine. I can hear no air leaking. An e-brake diaphram was changed and the bus did right for two mornings, then started same thing again. Second bus garage couldn't fix what they couldn't find. They heard no air leaking, either, but I lose 20 lbs of air pressure in a few seconds. I am perplexed. I am on the road with my family and need some advise, make that HELP!!!! |
Scott Whitney (63.151.68.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 22, 2001 - 12:58 am: | |
Hi Dave,
The fact that it builds to 80psi fine, and then has troubles after they seems like maybe it is something in the air suspension or auxillary air system? Maybe a check valve or something? But why you can't hear the air going anywhere is a mystery. Can you use shop air to pressurize the system, trying to repeat the events, so you can listen without the racket of the engine going? The air must be going somewhere.
I had a problem with an air cylinder gone bad. All the air was going out the exhaust of the air cylinder. It was going out very fast, but I could definitely hear a whooshing sound, and finally tracked it to the source. You might try taking a stick and hold one end to your ear and touch the other end to various air lines, valves, drain cocks, tanks etc. to listen. (Sort of like a crude stethascope) Or get a proper mechanic's stethascope. The air must be leaving the system somewhere - if nothing else, you should be able to determine which tank it is leaving from. Sorry, can't be of more help.
Scott |
Buswarrior (Buswarrior) (152.163.201.206)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 22, 2001 - 9:50 pm: | |
Hello Dave.
You need to get outside and all over the underside to locate where that air is going. Also try down through the little access panel in the floor at the back of the coach. It's noisey, but the compressor is right there too.
I'd be very suspicious that a valve of some kind is sticking open, and then finally works right. The 80 pounds starts getting close to the governor cut-in, and that is another little air event that works in mysterious ways. Unfortunately, the governor is mounted on the compressor, which is back in that roaring engine room. Also the air dryer purge valve likes to stick. Dryer is up under the front, behind the front axle.
When the air starts dropping, shut the engine off and then see if you can find the source. A bunch of assistants positioned around the bus would sure help here!
What year MC8? Before or after FMVSS 121?
Let us know some more observations, and we'll keep trying to help!
happy coaching!
buswarrior |
Scott Whitney (63.151.68.130)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, October 22, 2001 - 10:04 pm: | |
BTW, you probably know this. . . but make sure the bus is blocked before you go under it when on the air suspension. It is a life and death matter.
Scott |
Steve Gibbs (12.148.43.6)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 23, 2001 - 9:43 am: | |
Dave,
I recently had similar problem with the air dryer purge valve sticking open. I was not able to hear the leak after shutdown since air will only escape through that valve when the compressor is running. As stated before, apply shop air with the compressor located remote enough to avoid noise.
The purge valve is under the air dryer and the assembly can be removed without removing the dryer itself.
If it is passing air during the charge cycle then the valve is stuck.
Removing the govenor from the compressor will place the compressor in charge cycle and ensure that the govenor is not faulty. Just be ready to shutdown if the air starts to build or you will start blowing safety valves at about 135 psi.
Remember, air builds to service and emergency brake tanks first then a valve opens at about 80-90 psi to allow flow into the accessory tanks. Leaks in the air suspension system will drain this tank fast. Also if the bags or beams are leaking, they will have to be completely refilled at just about every restart.
The manual explains the air system very well and I am working on redrawing the line diagram since it is unreadable in most of the reproduction manuals that MCI supplies for the older models.
Hope this helps some.
Steve Gibbs |
dave spurgeon (206.148.81.2)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 25, 2001 - 12:35 am: | |
I took the advice of airing up using shop air. That allowed me to locate where the air is coming out. That's a start. I don't know the mechanics, but I'll try to describe what I found. On the rear of what I assume must be the compressor is a cylindrical shaped deal with a couple air lines going to it and a threaded hole, pointing straight up toward the access panel in the rear. Is this the govenor?
The air starts leaving the hole slowly at about 75lbs and increases loss rate till about 80lbs. This is where the needle stops. It then begins to drop back down to about 65lbs. I went thru this twice today, then I could feel the bus rising and I knew it had risen on up past where it normally was stopping. It got to 90lbs, buzzer went out and it went on to pop-off at 120lbs.
This has been going on for about two weeks. Once she airs up, there is no abnormality in the function of the system during the course of driving the bus. I am talking about for hundreds of miles. I have no problem shutting down to fuel, even for an hour, and then re-starting and airing back up normally.
My first concern is "Do I have a safety issue with this while traveling?" and my second is "Is this going to cause me to have to be towed?" I travel full-time as an Evangelist and my wife and three daughters travel with me.
I appreciate the responses and the advise I have received and pray the Lord Jesus Christ will bless you for it. I would also appreciate any other advise about how to remedy the problem. Are truck mechanics familiar with this type of compressor/govenor, if that's what it is? Are possibly needed parts available thru parts channels or are we talking MCI stuff.
By the way. My coach is a 1976 MC8. I don't even know what FMVSS 121 means. Again, thank you, and may God bless you. |
Scott Whitney (63.151.69.220)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 25, 2001 - 1:05 am: | |
Hi Dave,
Sounds like you have located the governor. At the risk of giving you bad advice, I hesitate to suggest what to do next, because I don't know if what you describe is the correct or incorrect operation of the thing. However, any truck shop can get you a replacement governor for about 25 bucks. If you have a some basic tools it might be an easy swap out to see if it solves the problem. Normally, I would try to determine, with certainty, the problem before just swapping out parts. . . but for the price a new governor, it might be worth a try if you are out of other options. Maybe someone else can describe the proper operation of this unit. . . At worst case you have a spare governor on hand for the future and have learned a bit more about your engine. . . What doesn't make sense is that if it IS a bad governor, why it would work eventually after finally airing up - since the governor cycles constantly while driving and using air for brakes etc.
Scott Whitney |
C. Ray Powell (Raypowell) (152.163.195.182)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 25, 2001 - 10:01 pm: | |
Scott, I still cannot access your web site for the camera info using http://63.151.68.130/wahoo3/bus/backupcam.asp
I don't know what IP address means.
Thanks
C Ray |
Scott Whitney (63.151.69.220)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, October 25, 2001 - 10:19 pm: | |
Hi C Ray,
Just after I posted that link, my IP address changed on me. . . sorry. Basically, every computer on the Internet is assigned a huge number called an IP address. Since humans stink at remembering lots of large numbers like that, we assign regular names to them, called domain names. (Usually just referred to as a Web site i.e. Yahoo.com, Amazon.com, Busnut.com etc.) But each of these names is actually just referenced to an IP address. Anyway, not meaning to bore you with Internet protocol, I host my Web site from home over my cable modem to save mula. The downside is that every now and then my computer's IP address changes rendering all links bad. . . And since I still have not come up with my bus name and hence new domain name, I just use the IP address. So, you can now access the camera stuff here:
http://63.151.69.220/wahoo3/bus/backupcam.asp
For how long, who knows. . . Last time my IP address stayed the same for about six months. . . .
Scott |
Steve Gibbs (12.148.43.7)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, October 30, 2001 - 12:08 pm: | |
Dave,
You have located the governor. It should have two lines attached. One line is monitoring the air pressure in the resevior tanks. The other line applies pressure to the purge valve on the bottom of the air dryer(between front wheels).
The shop air you hear leaking out of the governor is coming from your resevior tank and SHOULD NOT be leaking out. When pressure reaches "pop-off" this air is used to apply pressure to the compressor's unloader valves and back to the purge valve. You have a leaking governor and the good news is you can get a rebuilt one for about 19 bucks from www.mcicoach.com.
The bad news is that it should not fix itself and start building pressure. Nor should it be leaking enough to prevent buildup. However, it may be that after a couple of cycles it starts working fine.
Again, I would check the purge valve. Take it off and lubricate it to make sure its free in its seat. This started out as a very infrequent problem until it decided to stick open one day and I was going nowhere.
Good Luck,
Steve |
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