MY BUS STOPPED RUNNING! any suggestions

[Len Silva]

On a GM (my 4104) that's exactly what will happen if you try to start it from the rear without having the front run switch on.  It will run for a short while until enough air builds up to shut it off.

[chriss]

On a GM (my 4104) that's exactly what will happen if you try to start it from the rear without having the front run switch on.  It will run for a short while until enough air builds up to shut it off.

I did start it from the rear, but I had the front run switch on. The air pressure is down on the bus. I doesn't run long enough to build pressure.

[chriss]

Well, what was wrong with the bus?  Inquiring minds want to know.

I still haven't got it going yet. when I tried to start it today, It ran for about 30 sec. then slowly shut back down. then couldn't start it again. I checked the fuel filters and they were full of Diesel. I don't believe it was gas, because it smelled like diesel. I couldn't trace any gas smell. when I tried starting it back up, it puffed white smoke, so it seems to be getting fuel. I'm wondering if it could be an electrical problem? any suggestions?

thanks,
Chris 

This sounds a lot like an emergency shutdown like is found on the MCIs. I didn't think GMs had that, but maybe they do. 

First, do you have a switch somewhere (maybe in the engine compartment) for killing the engine that may be in the wrong position.

Second, when you started if, was the air fully built up. Try again, and this time, watch the shutdown cylinder on the engine. If it slowly pushes the fuel cutoff lever as the air builds up and shuts the engine down, then you have a problem with the shutdown system being activated. On the MCIs, the temp stats and oil pressure are hooked into this. There might also be water level sensors hooked into this. Usually, they activate by grounding, and the sensors can go bad. If you remove the wire from the terminal, it will disable the sensor, and should allow the engine to start, if that's what's causing the problem.

If it's not that, then it could very well have air in the fuel pump; possibly as a result of the turn into the fuel station, as I mentioned before. Your fuel pickup tube could be cracked or broken in the tank allowing it to suck air, or possibly the fuel level just got too low and you sucked air in when you turned. I've done many times.

If it starts, it's getting fuel. If it dies a slow death, it's running out of fuel for some reason. Probably one of the reasons stated above. Make sure you check the emergency shutdown flapper, too, in case it accidentally got triggered. I wouldn't expect it to start, though, if it is closed, as it wouldn't be able to get air to support combustion, but maybe there's enough there to let it run for a bit.

craig

I do have an emergency shutdown switch, but it shows that it is not engaged. I don't have any air pressure at all. It doesn't run long enough to build up. where would the flapper be located?
thanks
Chris 

[quantum500]

There is a 90degree housing right on top of the blower it should be there.  It is held open by a catch if you spring the catch it shuts with the help of spring.

[chriss]

There is a 90degree housing right on top of the blower it should be there.  It is held open by a catch if you spring the catch it shuts with the help of spring.

I'll check it out!
thanks for your help!
Chris

[makemineatwostroke]

Chriss;if you have a paper air cleaner check and make sure it's hasn't come apart,also there is a screen on top of the blower air inlet that will plug check all of your intake hoses make certain they are not collapsing you have a air problem somewhere if yiu are blowing some as it trying to start. does it blow black smoke when it starts    have a great day

[chriss]

Chriss;if you have a paper air cleaner check and make sure it's hasn't come apart,also there is a screen on top of the blower air inlet that will plug check all of your intake hoses make certain they are not collapsing you have a air problem somewhere if yiu are blowing some as it trying to start. does it blow black smoke when it starts    have a great day

no, it puffs out white smoke.

Chris

[chriss]

Well, what was wrong with the bus?  Inquiring minds want to know.

I still haven't got it going yet. when I tried to start it today, It ran for about 30 sec. then slowly shut back down. then couldn't start it again. I checked the fuel filters and they were full of Diesel. I don't believe it was gas, because it smelled like diesel. I couldn't trace any gas smell. when I tried starting it back up, it puffed white smoke, so it seems to be getting fuel. I'm wondering if it could be an electrical problem? any suggestions?

thanks,
Chris 

This sounds a lot like an emergency shutdown like is found on the MCIs. I didn't think GMs had that, but maybe they do. 

First, do you have a switch somewhere (maybe in the engine compartment) for killing the engine that may be in the wrong position.

Second, when you started if, was the air fully built up. Try again, and this time, watch the shutdown cylinder on the engine. If it slowly pushes the fuel cutoff lever as the air builds up and shuts the engine down, then you have a problem with the shutdown system being activated. On the MCIs, the temp stats and oil pressure are hooked into this. There might also be water level sensors hooked into this. Usually, they activate by grounding, and the sensors can go bad. If you remove the wire from the terminal, it will disable the sensor, and should allow the engine to start, if that's what's causing the problem.

If it's not that, then it could very well have air in the fuel pump; possibly as a result of the turn into the fuel station, as I mentioned before. Your fuel pickup tube could be cracked or broken in the tank allowing it to suck air, or possibly the fuel level just got too low and you sucked air in when you turned. I've done many times.

If it starts, it's getting fuel. If it dies a slow death, it's running out of fuel for some reason. Probably one of the reasons stated above. Make sure you check the emergency shutdown flapper, too, in case it accidentally got triggered. I wouldn't expect it to start, though, if it is closed, as it wouldn't be able to get air to support combustion, but maybe there's enough there to let it run for a bit.

craig

I just tried starting, and it ran until pressure built up and the shutdown cylinder pushed the cutoff lever, just like you mentioned, so it must the shutdown system. any other troubleshooting I can try in order to pinpoint?

thanks,
Chris

[makemineatwostroke]

disconnect your shut down cylinder and see if it will keep ruining the smoke part is what I don't understand, that is caused by fuel,air or low compression have a great day

[chriss]

disconnect your shut down cylinder and see if it will keep ruining the smoke part is what I don't understand, that is caused by fuel,air or low compression have a great day

I held the lever back manually, and it kept running just fine, so something is causing the shutoff to engage. 

[makemineatwostroke]

Chriss, follow your air line from the shutdown to the skinner valve (will have 2 air lines and 1 wire about 2 in round) and check for a broken wire or the valve itself could be bad ( power on closed, power off open to kill the engine) have a great day

[gumpy]

Again, is there a manual switch in the engine compartment for shutting down the engine, and if so, is it in the run positon. I'm not familiar with GMs, but the MCI has a switch that is basically run or off. If it's in the off position, it will act just like your's is doing. I'm not talking about the emergency shutdown switch, as that switch trips the air intake baffle. This would be a different switch that would shut down the engine normally from the rear control panel.

Next, disconnect the temp stats and oil pressure switch one at a time, trying to start between each. If it has an electronic shutdown system, these will be connected into it, and a sensor may be bad. If you starts and runs after you unhook a sensor wire, that's the bad one. Also check for a coolant level sensor and do the same with it.

craig

[jjrbus]

I cannot help much with a GM, but be very careful running the bus with the shutdown lever held open. You may have a real problem like no oil pressure or no coolant. HTH jim

[gumpy]

I cannot help much with a GM, but be very careful running the bus with the shutdown lever held open. You may have a real problem like no oil pressure or no coolant. HTH jim

Initially I was confused by Jim's statement, and reread it. He's absolutely correct. I've been telling you to unhook you sensors, but the first thing you need to do is make sure they are not activating for good cause. Make sure you have proper oil pressure and proper coolant level before continuing with my previous suggestions.

Thanks Jim

craig

[Beatenbo]

Sounds like a safety shut down. You said it ran a little the next morn. Try removing the air line from shut down valve an see if it contineues to run If air builds up and it shuts down could be a grounded shut down alarmstat or low oil, high temp ect.