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Old 10-27-2016, 02:32 PM   #1
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6BTA dies randomly while coming to a stop

'92 Blue Bird. I only have access to one side of the tank, as I don't have the key for the other side. Planned on drilling out the lock, haven't had a chance.

It's happened 3 times. I drive it 20-30 mins and it warms up, then I come up to a stop sign or light and it dies. 2 out of the 3 times its started right back up, 3rd time I had to use starting fluid.

How do the dual tanks work in these busses? I don't see a switch,m. My gauge reads half and I put some diesel in the driver side tank before it happened to me today.
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Old 10-27-2016, 03:10 PM   #2
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I would think that they would work like big rigs with dual tanks..... they have a line connecting them so if you only put fuel in one side it will eventually balance out between them.... and also the fuel draws from one tank and the return line goes to the other. But that's not a foregone conclusion, BB may have done it differently.
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Old 10-27-2016, 03:12 PM   #3
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Yeah just trying to narrow down to tank issue or fuel filter/pump related. It sat 8 Months prior to me buying it.
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Old 10-27-2016, 03:22 PM   #4
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A couple of quick and easy (and fairly cheap) things you can try....

Pull and drain the water separator.

Replace the fuel filters.

If it's an issue with fuel supply one or both of those may help. If not then you'll need to dig a little deeper.

I tend to think the fuel itself is probably ok, I'm presuming it was running all right prior to just shutting down?
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Old 10-27-2016, 07:42 PM   #5
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Yeah, it will start and run all day long, including idle. Just dies randomly when coming to a stop, most notably not on flat ground, but it has happened on flat ground once. Where's the water separator on these busses?
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Old 10-27-2016, 08:16 PM   #6
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It should be somewhere near the fuel filters... there are plenty of YouTube videos out there showing how to do this.
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Old 10-28-2016, 01:32 PM   #7
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Have you checked the fuel pick up(s) in the tanks?
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Yeah, it will start and run all day long, including idle. Just dies randomly when coming to a stop, most notably not on flat ground, but it has happened on flat ground once. Where's the water separator on these busses?
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Old 10-28-2016, 01:55 PM   #8
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I haven't. Going to check water traps and fuel filters first. Very familar with these motors in truck form, just not in a bus lol
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Old 10-28-2016, 11:27 PM   #9
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A lot of tanks have a filter inside. Not sure about yours but worth checking since it sounds like a fuel flow issue.
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Old 10-29-2016, 10:13 AM   #10
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Quote:
Originally Posted by AlleyCat67 View Post
I would think that they would work like big rigs with dual tanks..... they have a line connecting them so if you only put fuel in one side it will eventually balance out between them.... and also the fuel draws from one tank and the return line goes to the other. But that's not a foregone conclusion, BB may have done it differently.

That's only true of older trucks.

The government (in their infinite wisdom) at some point decided that crossover tubes presented an unacceptable risk of dumping all of your fuel on the road should it get broken.

They banned crossover tubes, and on trucks made since then you see all kinds of crazy BS involving float triggered switches for tank-to-tank transfer pumps, and return line pressure monitors to decide which tank to return fuel to, and a number of other things that engineers dreamed up to make a two tank design work without a crossover.

That's not to say the old crossover tube system was perfect either. I have a Mack Superliner that a previous owner put an aftermarket fuel pump/dryer system on while doing some hot-rodding work. That thing moves a tremendous amount of fuel. Enough that with a slight blockage in the crossover, after running for about 45 minutes the right tank was completely empty and the left tank had plenty of fuel in it. In the amount of time it took to drain some fuel to fill the fuel filters, the fuel level had evened back out. Just had to stop every 20-30 minutes and shut the engine down for a couple minutes, let some fuel move from the return tank to the supply tank, fire it back up and head on down the road. Got it back home, cleaned the tanks, put a bigger crossover on it, and haven't had a problem since.
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Old 10-29-2016, 02:31 PM   #11
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Quote:
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The government (in their infinite wisdom) at some point decided that crossover tubes presented an unacceptable risk of dumping all of your fuel on the road should it get broken.
If it was the government that stopped this practice, then all I can say is... I agree with them wholeheartedly!

If I were designing a two-tank interconnected system there's no way in heck I'd put a tube that could break and drain the entire system only 6 inches off of the ground... No thanks.

It's my understanding that the most common system these days is to have a tee going to both tanks for intake and a tee going to both tanks for return. Basic hydrodynamics says that the more full tank will feed the intake first. Likewise, there will be a higher siphon effect pulling return fuel towards the empty side. As long as all the lines are equally clear and routed with minimal twists and turns it'll work just fine..
That doesn't address the issue of filling the tanks. I'm not sure how they equalize the tanks while filling. The simplest system would be to fill the tanks individually.
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Old 10-29-2016, 05:06 PM   #12
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On the big rigs (or anything else with dual tanks) that's what you do, fill them individually.

Hey, I never claimed to know HOW the tanks were interconnected, only that they are. A crossover line 6 inches off the ground is not a smart move... but they have to be connected some way.... I parked my truck one time and it was leaning at about a 15-20 degree angle with the driver's side lower.... some way most of the fuel drained out of the right tank into the left, and the engine was NOT running. When I moved it back to level ground they equalized again... again with the engine NOT running.

This was some hole in the wall truck stop up north, can't remember now where it was, all the parking was full except up on a hillside.... needless to say that wasn't a comfortable feeling (I had a high COG load) so I moved as soon as a spot opened up on level ground.
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Old 11-03-2016, 10:18 AM   #13
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Check all fuel line connections. If they are only leaking slightly they can pull air in the line shutting down the engine.
I had some connections on my 1992 TC2000 that were leaking and it would shut down at idle.
I went through and replaced all of my fuel lines, from the fuel tank to the engine, resealed or replaced fuel fittings.
That made things better for me.
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Old 11-03-2016, 10:48 AM   #14
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Years ago, I came within a whisker of dumping almost 200 gallons on the road, after running over some metal debris which bounced up and hit the bottom-to-bottom crossover line.
If you must have one, the fittings and line should be behind the tanks, not below.
I would see about a larger tank, rather than installing a second.
If your bus came with two tanks and old-fashioned bottom crossover, you might want to take a real good look at it and see if you can protect it better.

As for the stalling engine... what the others said about filters.

On Millicent, air in the lines affected cold starting only. When I bought her, she needed very long cranking to start after being parked.
That turned out to be the fuel return hose, which had become porous with age, and air molecules snuck in when she was parked. Yes, the return line, which makes little sense to me. But that's what it was.
So for the stalling problem, I would start with the filters.

Also, what's the idle speed? Can you "save" the engine by taking the transmission to Neutral?
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Old 11-11-2016, 07:51 PM   #15
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Lift pump is leaking. I could never see it because it was parked in the grass. Have a nice big puddle under the bus.
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Old 11-11-2016, 09:22 PM   #16
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I replaced Millicent's lift pump recently -- 1992 model.
My local NAPA Auto Parts had the pump in stock, because it is also used on Dodge pickups.
It was a straight forward enough job -- two bolts, assorted fittings. I may have run back to the store for a fitting or two, since the replacement pump had just slightly different connections.
Keep the new pump straight as you bolt it on, so the push-rod goes where it belongs.
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Old 11-12-2016, 03:40 PM   #17
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Thanks, Cummins has a warehouse here in Austin, so I'm just going to grab one from them on Monday. There is a difference in lift pumps from what I've seen.

Also, I think part of the problem is an incorrect reading fuel gauge. It sits at half so I've only put diesel in it once. I foresee myself dropping the tank in the future to replace the sending unit.
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Old 11-12-2016, 04:04 PM   #18
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Quote:
Originally Posted by Onetype View Post
Thanks, Cummins has a warehouse here in Austin, so I'm just going to grab one from them on Monday. There is a difference in lift pumps from what I've seen.

Also, I think part of the problem is an incorrect reading fuel gauge. It sits at half so I've only put diesel in it once. I foresee myself dropping the tank in the future to replace the sending unit.
on a Bus you should have an access plate in the floor that you can pull up that is above your fuel tank.. then you can service the sending unit from up above..

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Old 11-12-2016, 05:26 PM   #19
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Yeah, that would be awesome if not for the hardwood floor, and subfloor.
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Old 11-12-2016, 06:09 PM   #20
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Yeah, that would be awesome if not for the hardwood floor, and subfloor.
4 plunge cuts with a circular saw and there you are.
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