Bus wont start

[joedelauter]

some additional clarification.
The bus is a 1988 MCI 102 A3.   DDEC 6V96.   Auto transmission - Allison 4 speed.

[jraynor]

So your bus is only a few years older than mine. seems like the only thing different is the fact that yours is a DDEC. Send me your email in a personal message and ill send you the transmission section that I have to see if I have the missing pages you need. In the mean time I will look at some schematics to see how the neutral plays into starting to see if I can locate where the switch is

[joedelauter]

Email is:  joe.delauter@homeinstead.com
The manual i have - cover page has following:  MCI 96-102 series model, Maintenance Manual.  TMC, Roswell, NM, Custom Coach, Columbus Ohio, MCI Pembina, North Dakota, Universal Coach Parts, Inc., Des Plains, Ill.

[luvrbus]

Ok,it has a 740 Allison the neutral switch is on the drivers close to the shift linkage it has 2 wires pull the wire and use a paper clip to jump with and if starts the switch is bad and he won't have a DDEC engine unless some installed another engine.A 88 model would have been a DDEC 1 and I never saw a DDEC 1 in a MCI they used 2 -boxes on the DDEC l

[jraynor]

Ok,it has a 740 Allison the neutral switch is on the drivers close to the shift linkage it has 2 wires pull the wire and use a paper clip to jump with and if starts the switch is bad and he won't have a DDEC engine unless some installed another engine.A 88 model would have been a DDEC 1 and I never saw a DDEC 1 in a MCI they used 2 -boxes on the DDEC l

After looking at the diagram for the bus, I think the neutral switch is actually on the transmission itself. From rear junction box stud #24 or #25, a wire labeled 3-BK-16 (so its a 16 gauge) wire goes to the neutral relay terminal 7. This is an icecube style relay with only 4 terminals being used. From terminal 2 of that same relay, the same nomenclature on the wiring runs to the neutral switch and then to ground.

So with it coming from the rear junction box, I believe that its on the transmission. Plus I have looked in the shifter tower and I don't think there is a switch there that the lever hits. I know there is sometimes a switch there for the park break that is used for the retractable step

[joedelauter]

Jonathan,
Thank you,
The rear junction box.  help me with this.  Where is that box located?
The Neutral relay indicated on the diagram - is that a unit that we would replace?

On the tower, there is a separate area where there is the parking brake lever.  It is a push pull type of knob.

[jraynor]

Jonathan,
Thank you,
The rear junction box.  help me with this.  Where is that box located?
The Neutral relay indicated on the diagram - is that a unit that we would replace?

On the tower, there is a separate area where there is the parking brake lever.  It is a push pull type of knob.

open the side door behind the rear tag axle on the drivers side. it is to the left of the air intake. Not the easiest to really access and debug. And no, the relay is is not the item to replace, this is just what to look for to follow the wire that should lead out to the transmission to where the neutral switch is. That neutral switch may be your issue.

Just thought of this: Have you tried to shift just outside of the neutral position on your shifter to see if maybe the cable needs to be adjusted?

[joedelauter]

Thanks for sticking with me on this.
We moved the shift lever several times through the gears and jiggled it over and over.  It did catch one time and started.  Several days ago.  But we cannot seem to get it to catch.
That is what led me to think that it might a a unit that can be replaced or fixed.  But if it might be a cable, how do we diagnose this and then what is the process to adjust - correct?

[luvrbus]

Just take a light and look on the drivers side of the transmission at the linkage if you see 2 wires that is your neutral switch start there bypassing the switch, it relieves a lot of heart burn and saves a lot of time wasted chasing the circuit.To check the adjustment just hold the starter button down and move the shift lever in both directions.If the fuel pressure switch goes bad your MCI will start either     

[joedelauter]

If this works, what would the adjustment be to correct?

[jraynor]

Thanks for sticking with me on this.
We moved the shift lever several times through the gears and jiggled it over and over.  It did catch one time and started.  Several days ago.  But we cannot seem to get it to catch.
That is what led me to think that it might a a unit that can be replaced or fixed.  But if it might be a cable, how do we diagnose this and then what is the process to adjust - correct?

I would troubleshoot the neutral switch first. you can bypass it more easily by taking the ground directly to terminal 2 of the relay base. Disconnect the existing terminal connection and connect the terminal to ground as shown in the picture. If it starts, then you'll have to go deeper into why the neutral switch isn't working anymore (or why its working intermittently) or adjusting the cable can still be the fix. I wouldn't mess with adjusting the cable unless you can repeatedly get it to work by slightly moving the shifter. (verification by reproduction)

If it doesn't start, then its another issue

[luvrbus]

We still need to find out if he indeed does have a DDEC engine I never saw one in that year model of a MCI but it is possible he has a DDEC a photo of the front top  of the engine would clear that up,if he has a throttle cable with air cylinders on top it's a mechanical engine and he can stop looking for a plug in port   

[jraynor]

If this works, what would the adjustment be to correct?

Joe,

Take a picture of your engine from the back with the doors open. Try to make sure you capture the top portion of the motor as well near the turbo. trying to find a picture with one and one without but im having trouble finding one

[jraynor]

So I found these 2 images. The red engine is about as close as I could get to finding one with the DDEC. apparently DD mounts the Boxes in different places on the engines. saw a really good picture of one before but I never saved it

[luvrbus]

They are all mounted there on the 2 stroke engines they set on top of the governor