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Old 11-26-2017, 10:44 AM   #1
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HELP my bus won't start.

These are words I see way too often, usually from nu bees and it just isn't necessary. Often followed by "I took out all of the xxxx wiring and now it won't start". Often it's after taking out the door and hatch switches.

Just a little background, I was an electrical troubleshooter on ground equipment in the Navy, had my own import repair shop in the 70s, worked at a restoration/import repair shop where I did most of the electrical work. Some of the more memorable were Lamborghini ( all the wires were the same color, no wiring diagram) Porsche,( tiny wires with a relay on pretty much every circuit, short in one of their molded plugs caused main harness to melt together) 29 Ford (complete rewire for "fail safe" Great American race) on the rare occasions that I had a wiring diagram I had to translate to English. Thankfully that was just colors. Granted this was all pre computer.

For those who don't have any electrical experience and don't understand electrical diagrams. If you want to disable the door switches. UNHOOK ONE AT A TIME and see if the bus will start. For the most part a door switch is normally open meaning that when the door is open the switch is open meaning the circuit is not complete. If the bus won't start after unhooking a switch tie the wires together and see if that works. If you want to completely remove the wiring for some reason. Locate the other end of the wires ONE CIRCUIT AT A TIME and do there whatever you did to them at the switch end to make the bus start. Check to see if the bus still starts, if so it is now safe to remove the wires.

"The engine turns over/cranks but still won't start so I replaced the batteries and it still won't start" Really? I've read this a few times in the last few months. I believe that one even said a dealer told him to do that. IF AN ENGINE CRANKS AT A REASONABLE SPEED THE BATTERIES ARE NOT BAD, don't go buy new ones.

The very first thing I would do is go to the starter and energize the solenoid. (make sure trans is in neutral and brakes set, chock wheels). If the engine turns over at a reasonable speed, starter is good, batteries are good and battery cables are good. (You should clean them anyway). Now, put a test light on solenoid energize wire and turn key to start position, it probably won't light.

If it cranks/turns over but won't start. Go to the unit that is supposed to get power when the key is "on", on pre computer models, probably the fuel cut off, post computer probably ecu.

I usually work backwards from what is "supposed to work"

With the exception of the rear engine buses a school bus is a truck with different body on it. The main chassis wiring came from the manufacturer of the truck part, IE, Freightliner, International, etc. The bus manufacturer has added the interlock bits to the original wiring. The newer one were probably ordered with plug "123xyz" so that bus manufacturer can simply plug into it and have everything work.

Dick
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Old 11-26-2017, 12:34 PM   #2
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dont you wish they would read this before cutting wires?
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Old 11-26-2017, 01:53 PM   #3
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Quote:
"The engine turns over/cranks but still won't start so I replaced the batteries and it still won't start" Really? I've read this a few times in the last few months. I believe that one even said a dealer told him to do that. IF AN ENGINE CRANKS AT A REASONABLE SPEED THE BATTERIES ARE NOT BAD, don't go buy new ones.
As an auto tech with over 20 years' experience, I disagree, when dealing with computer controlled motors. That might be true in the 1970's.

If the battery has one weak cell, its voltage may drop below 10V while cranking, even though the motor spins fine. The low voltage confuses the computer, or won't allow it to work at all, on some vehicles. Check the voltage at the battery with a voltmeter while cranking.

Many a vehicle I have seen have this problem. A new battery fixes it. Just don't confuse it with a lame alternator. Then just give your battery a good charge, and install a new alternator. My bus wouldn't start in cold weather with one, new, 810CCA battery. It spun just fine., but the voltage was dropping. Two connected in parallel, and it is OK, and starts immediately.
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Old 11-26-2017, 02:23 PM   #4
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Maybe a sticky titled "Read B4 disconnecting door buzzer/ interlocks" then those posting that question could just be given link to that thread to create a nicemoment.
And fixes/ discussion for that issue will all be in one place instead of searching thru builds/ threads for one persons fix.
Doug
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Old 11-26-2017, 02:48 PM   #5
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Quote:
Originally Posted by Mountain Gnome View Post
As an auto tech with over 20 years' experience, I disagree, when dealing with computer controlled motors. That might be true in the 1970's.

If the battery has one weak cell, its voltage may drop below 10V while cranking, even though the motor spins fine. The low voltage confuses the computer, or won't allow it to work at all, on some vehicles. Check the voltage at the battery with a voltmeter while cranking.

Many a vehicle I have seen have this problem. A new battery fixes it. Just don't confuse it with a lame alternator. Then just give your battery a good charge, and install a new alternator. My bus wouldn't start in cold weather with one, new, 810CCA battery. It spun just fine., but the voltage was dropping. Two connected in parallel, and it is OK, and starts immediately.
some navistar engines have a minimum RPM reading required to start the engine... I think a 444E is 160 and above (ill have to verify that in the book).. so just because it spins doesnt mean it will start.. weak or discharged batteries show themselves in many mysterious ways on these electronic engines..

-Christopher
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Old 11-26-2017, 03:04 PM   #6
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Interlock issues are a certain constant on this sight. There is no one size fits all fix. Many of us have the interlock to thank for a painful educational experience to varying degrees.

Like others here I also have learned to appreciate the buzzer when I occasionally forget to latch a door properly, usually when I'm fatigued.

You're not the first person to want to hack out all that wire. We all feel your pain on this subject.
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Old 11-26-2017, 03:16 PM   #7
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in my opinion, save the WIRE even if the circuit gets disconnected... when i took out a wheelchair lift I save the Wires.. sure made it easy when i wanted to hook up an auxilliary light .. I didnt have to run a wire all through the bus... the exsting wire was a nice 12 gauge.. toned it to the switch panel and bam.. easy for a light.
-Christopher
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Old 11-28-2017, 05:14 PM   #8
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Starting and interlocks

As i am learning this lesson the hard way right now, one of the big things that would have helped me is if i labeled each wire as i took a dome light off or unplugged a window or escape hatch. Take note of every wire, its color and the number printed on the wire itself and what it went to. Its too easy to get overwhelmed with the number of things that have wires going to them and confuse a dome light wire for a window or hatch wire. (for my vehicle the emergency windows, hatches and rear door interlock wires were all pink wires and so far they were the only pink wires. )

The interlock for those new to buses is a way of disabling the starter on a vehicle is one of the emergency windows or a hatch is open to ensure the safety of children. Disable these at your own risk and please make sure that your children are safe.

For my vehicle the interlock was in the form of an old starter solenoid with ground supplied to the center post from the rear door switch. I bypassed it by removing the two outer wire and joining them together.

An example of the solenoid is here https://www.macsautoparts.com/ford_m...passenger.html

A way to test it is to use a test light like this one https://www.autozone.com/test-scan-a...ter/186543_0_0

youtube instructions on how to use it if you never have. basically if you plug the end of the test light to the positive of the battery and touch a grounded circuit, the testlight bulb with light up as a bulb only needs power and ground and you are already supplying the power. This also works in reverse, if you clamp onto ground and touch a power circuit, it will light up. Test the center post to ensure it is getting ground. If not, thats why your bus isn't starting. Close the rear door, test the ground at the rear door, repair any cuts you made in the wire going from the solenoid to the rear door, etc. as long as you have ground on the center post of the solenoid, test for power on both sides of the solenoid. There is a direction of flow, meaning when you turn the key to start, one side of the solenoid should be getting power. As long as ground is present on the center post, the solenoid will connect the outer posts and allow power to go to the other wire. This can be bypassed by pulling the outer wires off and connecting them together. If you would like, they can be shortened quite a bit by tracing them back.

The buzzer for my bus was a simple matter of removing the pink wires from the one side and removing then joining the three black wires together from the other side.
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Old 11-28-2017, 06:59 PM   #9
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I took a different approach on my first bus. I found my framing hammer and pounded the buzzer until it didn't buzz anymore. The interlock system worked silently.

I don't disable the interlock system any more. There's been a couple times when it stopped me from a mistake.

You're actually making progress, so kudos.
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Old 11-28-2017, 09:48 PM   #10
Mini-Skoolie
 
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I think i like your method with the framing hammer better, gotta try that next time.
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