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Author Topic: Ignition problem - MCI '79 - need some help please  (Read 2107 times)
tnichol
MC-9 1979 - A work in progress
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« on: July 14, 2013, 01:35:40 PM »


Hey - I'm stumpped ( yes, again! )   Undecided

I'm a semi-happy owner of an MCI '79.  I'm about 80% of the way through the conversion.  We use it mostly for football games, and some small camping adventures...

Anyway - I've kept it running pretty well, regular service for the last 3 years.  All has been pretty well - but I'm now unable to get it to start. I mean - when I press the ignition button ( A below ) NOTHING happens - its like there is an override on, or something is dead. The battery is DEFINITELY charged.  I can hear the "low pressure" buzzer going as always).  I'm in neutral, with the brake engaged. Its all like it always has been - but this time, I'm missing something, or something has changed.

I'm thinking maybe I need to Hot wire it in the rear? I'd love some suggestions on a) what I should do, or b) instructions on how to hot wire this, so that ignition in the rear will work.

Oh, another detail.  I've never really understood the rear ignition option.  I think at some point it worked as designed. Because I remember pressing that toggle down ( B below ) and having the engine turn over... but now ( and for QUITE some time this has been the case.. NOTHING happens when I press B).  So - I've for at least a year been able to start it ONLY in the front ( A ). So - maybe the switch in the rear is bad? Bad wire somewhere? Short? I'm not sure - love your suggestions.   Oh, and YES I turned ON the Power/kill switch in the front ( the photo shows it off, sorry ).

ANY suggestions, no matter how simple are welcome.  I don't mind at all - just want to get it going again! I'm totally ok with a hacked/hotwired solution in the rear if thats the solution - but I'll need some idiot proof instructions on how to do it. 

First though, if you think I'm missing something.. or go cutting 30+ year old black stained wires.. I'd like to hear them

Thanks in advance!

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Dave5Cs
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1979 MCI MC5Cs 6V-71 HT-740 Allison, Roseville, CA




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« Reply #1 on: July 14, 2013, 01:48:24 PM »

After you turned your kill switch back on did you go to the back and reset your airn flapper. There is a little lever that you pull down until it clicks into a detent that holds it opened.

Dave5Cs from Galaxy S III
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Dave5Cs
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1979 MCI MC5Cs 6V-71 HT-740 Allison, Roseville, CA




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« Reply #2 on: July 14, 2013, 01:52:33 PM »

Also the back start will only work if you turn the key to on if you have one or flip the key or on switch first and then go to the back and hit that start switch.

The lever is on the right or passenger side of the motor back side door look up on the back side of the air intake you should see it. Pull down until it locks in place that opens your flapper shut down.

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tnichol
MC-9 1979 - A work in progress
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« Reply #3 on: July 14, 2013, 01:57:24 PM »

NO I definitely did not, because I don't know what or where that flapper is.  can you please explain it in slightly more detail and I'll try to find it? Its in the rear - like in the main compartment behind the double doors in the rear, or behind one of the smaller doors in the rear on the side in back?

Tim
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bevans6
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« Reply #4 on: July 14, 2013, 02:11:53 PM »

Here is a link to the relevant section of the manual.  http://www.buses101.com/PDF_Files/MCI%209%20Maint%20Manual%20in%20PDF%20format/MC-9%20-%20Maint%20Manual%20Section%207.pdf

You can start to investigate, learn the names of the switches, etc.  The front switch that you call the power/kill switch is called the master switch, it needs to be on for the rear switch to work.  If you tripped the emergency shutdown, it's a flap inside the cover on top of the blower with a big round electrical solenoid to operate it.  The most likely place to start is to get a test light and see if the solenoid on the starter is getting +24 volts when the starter switch is pressed - either one, the front one you call an ignition switch (diesel engine, no ignition switch) or the rear one that you have great pictures of.  They send a signal to a relay in the rear electrical box which sends a signal to the starter motor solenoid on the start motor.

Stupid thought - the battery disconnect switch in the front luggage bay is on and good, yes?

Don't start cutting wires, that would just be dumb.

Brian
« Last Edit: July 14, 2013, 02:15:43 PM by bevans6 » Logged

1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
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« Reply #5 on: July 14, 2013, 03:01:37 PM »

Tim,

Sounds like the problem is that the engine wont crank. The emergency flapper won't affect that. It may keep the engine from starting, but won't prevent it from cranking.

When you say the battery is charged, you should have 2 batteries in series for your 24 volt system, unless your bus has been converted to 12 volt. In my mind, the batteries may have enough charge to operate the low air pressure alarm, but not enough to crank the engine. I'd be load testing the batteries, first thing.

What you are calling the ignition switch, I would call the starter button. Your on-off switch to the left of the starter button energizes a master relay in the front electrical compartment. If that relay is not working, you won't be able to operate the starter motor.

If your MC9 is an ex-hound, most of those had a hidden anti-theft device whereby you had to turn the chime switch on in order to crank the engine. That switch is on the switch panel by your left leg. Don't know if that applies to your bus or not. 

Bob
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P8M4905A-1308, 8V71 w/V730
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tnichol
MC-9 1979 - A work in progress
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« Reply #6 on: July 14, 2013, 05:37:06 PM »

OK thanks all for the good suggestions, and the patience with me being a bus newbie.  Sorry about the names being wrong on the pictures for the buttons/switches.

Yes BOTH batteries are fully charged. Thats always been my first step.  Yes I also confirm that the battery disconnect is  (OFF) in the up position thats confirmed because of the buzzers and the lights are on.  I always disconnect them when its going to sit for a bit.  I know I sound like I just picked it up today - but I've been driving it for better part of 3 years now.  I agree if I'm asking for help, I should use the right terms. 

I have no key - only the master switch.  It was definitely ON before I pushed the starter button.  Again on mine - the buzzer for the low air pressure is blissfully silent when that master switch is off.  Thanks again for the coaching on the names of the buttons.  Tomorrow morning I'll check the chimes switch - thanks for that tip.

Just to be really clear - there is no sound at all to indicate the starter is getting any power - I hear nothing, no crank, no attempt, no click to indicate the starter has engaged.  There is no sound from the front starter button, nor the rear starter switch.  But as I said, that rear starter switch has not seemed to work for some time - I remember it working at one point, but not for a long time. I've been starting it in the front with the starter button.  Its never failed to fire for me before since I picked up the bus in 2010.

Thanks again guys. I'll try to locate the flapper in the back, and the chimes switch in the front. 

Tim
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Rick 74 MC-8
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« Reply #7 on: July 14, 2013, 06:36:26 PM »

Tim

 There is a small wire coming off the starter motor solenoid ( curbside rear engine compartment) it runs to the top of the fuel filter and then to ground
 check those connections and maybe jump them to ground. It is a fuel pressure cut off switch if its not grounded or the switch fails the starter solenoid will not engage. It's part of the safety shut down system it disengages the starter as soon as it gets fuel pressure

Rick
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challenger440
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« Reply #8 on: July 14, 2013, 08:19:42 PM »

Can't start my mc7 without the step light and chime switch in the on position.  Early anti-theft I guess.  Power is on at the dash but it will not start.  j m
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John M.
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bevans6
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« Reply #9 on: July 15, 2013, 04:07:57 AM »

The starter motor section of the manual I gave you the link to starts on page 7-15, there is a generous section on troubleshooting the motor itself but the motor is probably fine.  The first step I would take is to test the starter motor itself.  You can test that by momentarily jumping the low-current solenoid terminal on top of the motor itself to +24 volts, that bypasses the whole starter control section of the wiring except for the fuel pressure switch.  The fuel pressure switch is mounted on the secondary fuel filter head and it provides the ground path for the solenoid - it's normally closed and opens when there is over around 7 psi of fuel pressure so you can't crank the motor when the engine is running.  So if your test of jumping the solenoid connection fails then try bypassing the fuel pressure switch and connecting the solenoid ground connection directly to ground.  If you do that and the starter motor still won't spin when you jump the low current lead to positive, then it's possible the solenoid is bad.  Your choice at that point (and what I would probably do) is take the starter motor to a repair shop and get them to overhaul it.  If you don't want to do that, then you can very carefully jump positive voltage directly to the high current post on the starter motor.  That should make the starter motor spin but since you aren't energizing the solenoid the motor should not engage the flywheel to start the engine.  But - this is potentially a lot of current and there could be sparks, welding and tears.  The starter motor control schematic is on page 7-48.  There are a lot of parts that need to work in order to get a positive signal to the starter motor solenoid, one is the neutral switch if you have an automatic transmission.  They are all there in the schematic.  If your testing shows that the actual starter motor works then I would personally just start working backwards and see where the signal gets lost.

Brian

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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Spicer 8844 4 speed Zen meditation device
Vintage race cars -
1978 Lola T440 Formula Ford
1972 NTM MK-4 B/SR
Dave5Cs
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1979 MCI MC5Cs 6V-71 HT-740 Allison, Roseville, CA




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« Reply #10 on: July 15, 2013, 07:42:27 AM »

I'm with Bob. Flip the chime switch.You probably hit it by accident. I ve done that before. The wife always asks if I did.lol

Dave5Cs from Galaxy S III
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tnichol
MC-9 1979 - A work in progress
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« Reply #11 on: July 16, 2013, 10:38:16 AM »

 Smiley Smiley Smiley Smiley Smiley Smiley Smiley Smiley Smiley Smiley Smiley

Thanks a million guys! It wasn't "just" the chimes switch though, I had to have all of the lights switches ( except driver light and hazard light switches ) ON.  Then the starter button worked perfectly and the bus started right up!

Thank you sincerely for the patience and coaching - I just knew that it had to be something stupid like that.

Respectfully,

Tim
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