starting problem

[harry]

1957 GM 4104 - starts -runs 7 minutes then stops - must wait about 1/2 hour before it will start again - then repeats - runs for 7 minutes then stops. Where do I look for the problem?

[TomC]

Try opening your fuel fill door to the fuel tank and then run it again.  If it doesn't stall out, then you have a blocked fuel tank vent.  Good Luck, TomC

[gumpy]

Wow Tom, you never cease to intrigue me with your interesting suggestions. I'd not have thought of a blocked vent on the fuel tank, but I see how that could cause the problem he's experiencing. 

I was going to suggest a cracked fuel line sucking air, but don't think it would restart after the first time.

I don't know much about the 4104, but I suspect they don't have the emergency shutdown system like the MCIs, which exhibit similar behavior if there's a bad sensor or the shuddown switch is in the wrong position. I suppose there might be a similar system on the 4104, and probably a rear kill switch that should be checked.

Oh, and the last suggestion I have... check the system snooze button. Maybe it's been wired backwards. 

[oldmansax]

Harry,

I don't know if the GMs have the same system as MCIs but you can check out this thread:

http://www.busconversions.com/bbs/index.php?topic=2448.0

[Jeremy]

Interesting...an unvented fuel tank can quickly stop a carburettor engine running, but injected petrol engines are usually immune as the much higher fuel pressure will overcome the problem. I had always assumed that the same would be true of diesel engines, which are 'fuel injected' too.

The cap on my Lexus doesn't have a vent, and after using a tank of fuel there is an incredible flow of air as you remove the filler cap - seriously - it feels like it's going to take your hand off sometimes.

Jeremy

[Lee Bradley]

Jeremy,
Fuel injected cars generally have the high pressure pump in the fuel tank and they use a sealed fuel system, to prevent unburned hydro-carbons from escaping to the atmosphere, with controlled venting to keep from collapsing the tank . The Detroit's have a low pressure transfer pump, to get the fuel to the injectors which provide the high pressure for injection, which would be easily stopped by a block tank vent. 

[Jeremy]

Got It!

Thanks

J

[gus]

A 4104 has a switch for mechanics to use to cut off the engine from the rear. If this is accidentally bumped it will do just as he said when the air pressure reaches 50-60 psi. It is easy to bump off when starting the engine from the rear. Don't ask me how I know this!

There are four switches there. One to take the starter out of the circuit so it can't accidentally be started, one to start the engine, one to shut off the engine and one for the compartment light.

These are located high on the right side of the engine compartment.

[harry]

Thanks everyone for the replys. I will try the vent cap first and then check the switches.
I have another 4104; that doesn't have a problem. So will check the switch positions on that one.

[Busted Knuckle]

Thanks everyone for the replys. I will try the vent cap first and then check the switches.
I have another 4104; that doesn't have a problem. So will check the switch positions on that one.

While Tom has a very good possible cause, I'd be looking at the shutdown solenoid myself as it usually takes 5 mins or so to build enoguh air for the cylinder to pressurize. Just my 2 cents worth! BK 

[Stan]

Like several others, I lean toward a fuel supply problem. If you start with no air pressure in the system, the seven minutes to shut down would indicate a problem in the shutdown circuit. However, unless there is a massive air leak, (air pressure back down to zero)  it should shut down almost immediately when restarted after 30 minutes.

To confirm if it is the shutdown circuit, just watch the top of the governor ater you start it. Shut down is done by an air cylinder piston extending and pushing on the shutdown lever. That is, air to the cylinder shuts it down. The air comes from a normally open solenoid valve which should be energized  (thus closed) when running.

[gus]

Harry,

You can't go by the position of the switches because they get changed over the years and are easily installed in reverse. 

On my 4104 the starter switch was a plain toggle, it is supposed to be a momentary-on type. One time Ileft it on  without knowing it. My starter wouldn't cut out after the engine started, a real disaster until I ran around and disconnected the battery. It was pure luck that I tried to shut it off just after starting it, otherwise it would have burned out the starter and maybe burned up the whole bus!!

After that I installed battery disconnect switches on all batteries.

[gumpy]

After that I installed battery disconnect switches on all batteries.

Hope you changed that switch, too!

[Hi yo silver]

Speaking of switches, many of you already know this, I'm sure.  I found out a source of heavy duty switches, relays, and such is www.colehersee.com.  Trust me, if I had any stake in this co. I wouldn't be nearly this poor! lol Happy Thanksgiving, all.  I'm thankful for people like you guys who share all so much.   

[harry]

To all who offered solutions or read the post.  Problem has been solved -- bus was parked on a slight grade and tilted to the passenger side - all air bags down. -- fuel level in tank was too low - engine would pull fuel  untill level dropped just below the pickup then stop - while engine was running the air bags would fill a little. After engine stopped fuel would bleed back down to the tank - this took about 1/2 hour - then engine would start again.  Added  50 gallons to tank - Problem went away.