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BUS not TRUCK

Posted By budx Friday, September 25, 2020 3:22 PM
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richard5933
 Posted Tuesday, September 29, 2020 3:58 AM
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Couple of things...

Could be that the auto shutdown system is kicking in for some reason. If your bus has one (they were optional) it senses low coolant, high temp, and low oil pressure. The way it works is there is a heat tab in a relay in the system, and when one of the sensors detects a problem a ground is completed to the heat tab. If the fault remains long enough for the heat tab to snap over, it opens the circuit and shuts off the fuel.

I have a problem in the shut down system on my '74 GM 4108 bus. Traced every part of the system and cannot find it. I finally disconnected one of the two wires going to the heat tab in the relay preventing the auto shut down from functioning. Means I have to watch the gauges carefully but it stopped the engine from only running a few minutes.

The other issue can be something as simple as a switch on the rear engine bay panel being in the wrong position. This is a very common problem, especially for first-time bus owners. The switch that allows you to start from the rear has three positions: front control, rear control, and rear start. It has to be in the front control position to operate from the front. There is also a on/off switch back there which sometimes trips people up, but it would stop the bus from starting in either position. Lots of times people use the rear start switch and then forget to put it back to the front control position.

Which particular bus model do you have? Do you have a manual for it? If not, I would be happy to post pages you need.

There are a few great bus owner forums out there with more information than you'll ever need. Also a few great resources for new parts for these buses.
Norm W.
 Posted Saturday, September 26, 2020 1:59 PM
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There should be a damper on the air intake, make sure that it is in the "Open" position. If the "Kill" switch has been moved the damper is probably closed. There is an air cylinder that shuts of the fuel by putting the rack in the "No Fuel" position. If the air is "0" on the gauge the engine will start, but when the air pressure builds, the air cylinder will shut off the fuel. The switches in the rear of the bus are usually, remote start, front start cut out (so the bus can't be started from the front, safety for the mechanic} and run switch. The front/rear start switch should be in the "Front" position in normal operation.
budx
 Posted Friday, September 25, 2020 6:38 PM
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Wolfcreek_Steve,

Thank you so much for ur reply. I bought the bus from an old (older n me) gentleman who has owned bus for 10+ years, lost his DL and told me bus just needed batteries to start and move. He knows nothing about bus wiring or mechanics. I side point all lights work, just the started switch stuck in cab stuck, kill and other switches on panel seem hard to push. As I said the engine starts immediately (after sitting 2 years) but shuts down after 2-4 (Or so) minutes. Truthfully I have no idea where the fuel solonod is. I know i know if a person doesn't know about somethng they should not not it. Thanks again.
Wolfcreek_Steve
 Posted Friday, September 25, 2020 3:39 PM
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Hot wire the fuel solenoid, (include a toggle switch to shut it down) fire it up and if it shuts down by itself, you have a fuel problem. If it doesn't shut down, you have a wiring problem.
Just a wild guess, is that there is a circuit with a timer in it to control idle speed and someone hooked that wire to the fuel solenoid. Someone with more knowledge of GM busses may have better ideas of what could be wrong.

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Central Wisconsin

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budx
 Posted Friday, September 25, 2020 3:22 PM
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I bought a 1964 gm pusher rvv'ed bus, has an 8v71. it starts perfectly from rear (buses have starter switch in rear) however will not start from cab, and it will only run about 3 minutes and shuts down. kill button front stuck, key stuck..... but why wont it stay running when starting from rear? and under control panel there is a zazillion wires, but most are just the normal wiring og a gm bus. CAN ANYONE HELP....IM IN OREGON.

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