6V92 starts, then shuts down

[chuckdrum]

Help!  I have a '79MCI 5C with a 6V92.  Haven't run it much this year but my most recent start (last week) was fine and a short outing about a month ago went well, too.  Then last evening I started it up, it ran for just a few seconds, then it shut down.  Subsequent tries were the same.  Maybe fuel related?  Fuel pump?  I'm nearly full on fuel.  The fuel filters are probably due to be changed (13K miles and 2 years) but I haven't noticed any loss of power or other problems until yesterday.

Also yesterday, I observed that the main belt (only one on this engine) had slipped off it's usual engine pulley and twisted onto the adjacent pulley.  I managed to muscle it around to the correct pulley and untwist it.  Haven't had that happen before and don't know if it relates to the shut-down problem.

I need to use the rig tomorrow and can't seem to find someone in the Seattle area who can check it out today.  Any help or hints would be appreciated.  Thanks!!

Chuck

[will4104]

I would suggest fuel filters first, then proceed from there. Simple stuff first then the more complicated, could be a myriad of things...

I'm not familiar with the coach you have but I'm sure more will respond who do...

Good Luck!

Will4104

[luvrbus]

Change the filters and prime it you will ok sounds like it lost the prime

[Jriddle]

You might check your rear start panel first.  Is the switch in the off position? Engine will start and when air pressure is enough to activate the shutoff the engine will die.
Been there done that LOL

John

[chuckdrum]

New development- Can't start it at all now.  Starter engages but doesn't have enough to start the engine.  Batteries are at 11.78V so it *should* start, right? Bus is plugged into shore power.

John- If you are referring to the panel at the back that gives you toggle switch options for front/rear start and engine shut-off, that is not operative on this coach.

luvrbus- haven't had to prime this engine how do I do that?

[bevans6]

11.78 is fully discharged, and it will never start with those.  They need around a 48 hour charge, although they might come back to around 80% after 6 hours or so on a 20 amp charger.  I would stop trying to start it at all until you have charged the batteries, you can do a lot of damage to the starter motor.  12.2 volts is 50% state of charge, 11.8v is officially zero, and fully charged is 12.7

Brian

[chuckdrum]

Thanks Brian.  Wonder why they are not being charged?  I have it on separate charger now.

Is it possible that when it started for me earlier there was enough juice to start but not enough to keep it running for more than a few seconds?  Or am I dealing with two separate problems here?

[bevans6]

If it is a mechanical governed engine then it "might" not need fully charged batteries to run.  There are some auto-shutdown systems that will turn it off if there is no electricity at all which may or may not be present and accounted for.  At the very least you need electricity to keep the engine stop skinner valve from opening.  I would get the batteries up to 12.7 volts and then see what happens.  Since it's an MCI I am presuming it has two batteries in series for 24 volts, and you can just charge them separately with two chargers, or one at a time with one 12v charger.  Aside from needing plus 24 volts to keep the engine stop skinner valve from opening, my engine can run forever with no electricity once it's running.  I once drove it 1200 miles with no alternator.  How big is your charger in volts and amps?

How long did it run before it stopped?  A few seconds can mean a couple of minutes for some people, to two seconds for people like me...  If it ran for long enough to get air pressure up to around 65 psi, then it might be an electrical problem telling the engine stop system to operate.  If it ran for 2 to 5 seconds, then it might have lost prime.  I have a priming pump installed on my engine but I don't know how to prime if you don't have a pump.  People use all sorts of inventive pumps and vacuum systems and garden sprayers and what not.  I am too dumb to figure out buck-shee things to do to prime it so I just went ahead and installed a little electrical pump.   

Brian

[bevans6]

with regard to charging, if your MC-5C has an alternator setup that is close to stock, it will not start charging until the air pressure gets up to around  70 psi.  There is an air pressure switch that turns off the field coil in the alternator.  The reason is that the stock alternator had an air cylinder to tension the belts, the idea being that if you needed to change a belt in the field you could dump the air, move the alternator over with a lever and the belts would all loosen.  Also to let the engine get running a bit before the load of the alternator and air conditioner could hit it, and to get enough air pressure for fast idle to work.

If you have the normal 8D starting batteries and they are fully discharged, as they seem to be, you can estimate the time to recharge by figuring that you need to push in about twice as many amps as you took out.  You took out 250 amp hours, that being the 20 hr discharge rate of a typical 8D battery, you need to put around 500 amp hours back in, 5 amp charger that is 100 hours, you get the picture.  This is just a WAG at predicting the recharge time, it's a lot more complicated than that.  I used to get peed off with my 5 amp 24 volt smart charger taking a week to top off my batteries until I figured that out...

Brian

[chuckdrum]

If you look up 'klutz' in the dictionary, you see a picture of me...

A tech came over to troubleshoot all this.  He hooked up a booster to the starter, it cranked over and quickly shut down, as before.  He said, "it's your Jake brake".  Well, this whole thing started with me trying to repair a non-functioning temp gauge which meant removing the dash plate/cover that houses said gauge.  The first switch next to the cover is the Jake brake, which I bumped into the 'on' position without knowing it.

The tech said the Jake normally cannot engage at idle, but did because of a (likely) bad switch that he identified to me.  I always just operate the Jake brake by manually switching in/out of it, so I had never been in idle before with the switch on.

I think I just temporarily drained the battery with my repeated attempts at starting and trying things... the battery is at about 12.6 now.

YAY!  Thanks for the input, Brian. Useful info.

Chuck

[bevans6]

Good for you, your bus works again and you've learned a few things today.    You could take a peek at Timkar's thread on the buffer switch, that is what normally keeps the jake brake from working at idle.

Brian

[luvrbus]

What is your address I am going to send you a used buffer switch for free it's bad business hooking those up direct but you must have good oil pressure   

[chuckdrum]

luvrbus-
Sorry, I didn't check back on this thread once I figured out the problem... Thanks for the offer of a free switch.  I'll send you my address shortly.

Since I only use the jake as needed and then shut it off, is a functioning buffer switch even necessary?  The jake seems to be working fine- used it a fair bit going over multiple hills last weekend.

Chuck

[bevans6]

The buffer switch is a "nice to have", it ensures that the jakes can only engage with the governor at no-fuel, so the engine can idle fine with jake switch on.  Now, I use my jake brake extensively in stop and go traffic, those annoying jams at construction on the interstate for example, and almost never on hills, so having a buffer switch means I leave my jake switch on and it lets me control my speed with all the little cars, and never tries to stall the engine when I shift gears or put in the clutch and slow down to an idle (mind you I also have a clutch switch in my jake control circuit so the jake cannot operate if the clutch is in).  I would absolutely install a buffer switch if I had jakes, in other words.

Brian