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Author Topic: 8v71 won,t stay running  (Read 3262 times)
4shore
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« on: March 21, 2009, 12:03:56 PM »

 Huh Well here is what I have done so far, let me preface all of this by saying the bus ran fine when I parked it; the engine lost prime so I got bug sprayer and connected to inlet on fuel filters (which were full before connecting sprayer) pumped about 2 qts fuel into engine then I unhooked sprayer and put plug back into the filters. I started the bus and the engine started but only briefly, rehooked bug sprayer refilled everything this time though I left bug sprayer hooked up refilled it and then while cranking engine I pumped the sprayer. Bottom line is I found out the engine will only run while I am pumping fuel out of the sprayer into the filters, sprayer gets empty the engine slowly runs out of fuel. I can repeat the process with the sprayer and it will start and run, although it will not run over idle. Any suggestions what might be happening. Thanks Guys for all of your help I appreciate it. Kevin

1978 mci 8
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NJT 5573
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« Reply #1 on: March 21, 2009, 12:14:53 PM »

Maybe you tripped the emergency shutdown. Did the air/electric shutdown stick in the closed position? Were the filters full when this started or half full or did you just start pumping before looking? How much fuel is in the tank? Did someone steal your fuel while parked?
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4shore
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« Reply #2 on: March 21, 2009, 12:19:44 PM »

The fuel filters were full before pumping, the bus is not out of fuel (little less than half) now the shutoff switch not sure I think it is located next to the fast idle switch, which way should the piston be to tell me if it is locked or not. Thanks
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4shore
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« Reply #3 on: March 21, 2009, 12:22:14 PM »

Let me clarify I believe the main shutoff in the blower is open and the bus would start and run but just until fuel in sprayer was empty.
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luvrbus
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« Reply #4 on: March 21, 2009, 12:30:30 PM »

You have fuel pickup problem check for stoppage or air leaks between the fuel pump and the tank, if that is ok check the pump starting with the drive  they do round out on the drive fork and the pump doesn't turn, then check the pump turning it with a drill in a small amount of fuel. The gear drive pump DD uses do not fail often. good luck
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blue_goose
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« Reply #5 on: March 21, 2009, 02:45:24 PM »

When it quits are the fuel filters still full.  If you have lost the fuel in the fuel line from the tank your fuel won't pick it up.  You will have to reprint the line.  There is a one way valve in the fuel line to keep it from returning to the tank.  If it is bad yo will have to replace it.  If you can connect a suction pump to the filter that will fill the line and filters.
Jack
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Don Fairchild
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« Reply #6 on: March 21, 2009, 02:57:40 PM »

While you may have a critter problem or a pick up issue,  If it will stay running when you prime it with the bug sprayer I would suspect the fuel pump gave up.

Don
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Van
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« Reply #7 on: March 21, 2009, 03:12:39 PM »

Dont know if the pump is the same as the 92 ,but sounds like the same symptoms I had when my pump went south,new pump and an electric primer pump in line plus new supply line from tank took care of the issues .good luck
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« Reply #8 on: March 21, 2009, 03:15:37 PM »

As Jack says, you have to make sure the fuel supply line from the tank to the primary filter is full. Either suck from the primary fuel filter inlet or pump from the tank.

When there is no air pressure the normal fuel shut off at the engine head is open even though the switch at the front is off. In other words, if there is no air pressure the engine will start even with the front switch off.

If there is an engine run switch closed somewhere that valve will close when air pressure builds up. There is also another engine run switch back at the engine for mechanic's use. Sometimes this switch gets bumped accidentally (Don't ask me how I know this!). Check this switch.

Also, as Jack said, check the fuel supply line check valve, usually at the primary fuel filter inlet. Mine failed and did just like yours is doing now. This is a very simple but important valve.

Remember that your engine fuel pump sucks through the primary filter and pressurizes the secondary filter. In other words, the fuel pump is between the two filters.
 
So, you should be pumping into the primary filter, not the secondary filter, so you prime the engine pump in the process.
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« Reply #9 on: March 21, 2009, 05:02:02 PM »

Martha go get me the shotgun, we's going hunting buses...

Sheesh. Settle down. Read what he wrote.

Before we scare 4shore silly, or convince him to replace the entire fuel system, now that we listed pretty much all of it....I'm surprised no one thought to mention anything grave about the injectors....

4 shore, go with Don's hunch first, confirm or deny the fuel pump is able to move fuel, then get back to us.

There are times when this board is a hindrance to finding the problem.

happy coaching!
buswarrior
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Lin
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« Reply #10 on: March 21, 2009, 05:28:11 PM »

How did the engine lose prime?  That does not happen just randomly.  Perhaps there was no prime issue to begin with, just the fuel supply problem.
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4shore
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« Reply #11 on: March 21, 2009, 05:35:45 PM »

Thanks everyone for your response, I am leaning towards Dons reply. When I originally started the engine it only ran a few seconds and shut off. I checked fuel filters they were full of fuel, I then went through the above steps.
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busshawg
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« Reply #12 on: March 23, 2009, 12:19:20 PM »

How's it going? or should I say running. Another issue that might be food for thought is a collasped fuel line? Just a thought , I did have that happen to me once. With the engine trying to suck the fuel the line may just be collapsing?
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4shore
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« Reply #13 on: April 04, 2009, 03:03:45 PM »

Ah yes sweet music today as she fired up after a fuel pump replacement and a few lines and fittings. In my humble opinion the 8v71 is one of the best engines they put in a bus; especially for the application we use. Everything is pretty much mechanical no sensors or computers needed to diagnose. I do drive a truck and have done so for over 25 years and the new engines are okay but there are still issues with them. Thanks for all of your help. Kevin
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buswarrior
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« Reply #14 on: April 06, 2009, 07:38:12 AM »

Excellent report.

Score another one for Don.

happy coaching!
buswarrior
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bobsw
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« Reply #15 on: April 06, 2009, 08:50:29 PM »

A lot of people say that the fuel pump on the 8-71 / 8-92 are almost bullet proof but I have had to replace mine twice. This is one of the spare parts that I don't travel without.
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« Reply #16 on: April 06, 2009, 11:55:00 PM »

Here at Big Transit, with a forest of 6V71 running not so long ago...

I have a distant memory, oh, back a decade or a little more, about a broo-hah-hah over the drive for one of the accessories.

The one that was being used was failing prematurely, and there was an upgraded one. One cast, one machined.

Wonder if it's related...?

happy coaching!
buswarrior

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JackConrad
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« Reply #17 on: April 07, 2009, 04:34:58 AM »

I recently watched a mechanic replace the fuel pump on a  8V92.  He also replaced the little "drive thingy". When I inspected the drive , I noticed it was not cast and that both of the "ears" were bent slightly. I do not know what caused the ears to bend slightly, but the mechanic said "that is why I always replace the drive when replacing a pump"  Jack
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« Reply #18 on: April 07, 2009, 06:57:37 PM »

I did it right the second time and replaced the drive ears.
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« Reply #19 on: April 07, 2009, 07:24:37 PM »

I have an extra fuel pump that I found in the bus when I got it.  How would I tell if it is any good (without installing it, of course).
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« Reply #20 on: April 07, 2009, 08:01:27 PM »

First check the voltage, then take the pos wire and put it on a good batt, tapping the ground wire on the post to see if you have fire.

~Paul~
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Lin
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« Reply #21 on: April 07, 2009, 08:33:15 PM »

It's a mechanical fuel pump like the one on my 8v71 engine.  Sorry I did not mention that.
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Van
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« Reply #22 on: April 07, 2009, 08:42:48 PM »

In the manual ,when replacing the fuel pump,it's strongly advised to check the little drive connector plate when removing the pump.Bringing our Eagle home blew a fuel pump in Amarillo,fuel pump main shaft sheered in half due to fuel starvation (collapsed supply line),new pump and 1 drive key later back on the road.

to check the pump you will have to disassemble the pump and inspect the drive gear,pinion ,bushings etc.try turning the square end of the drive shaft,any major resistance? Usually there is a big core charge ,you can get them new(reliabuilt)from DD,a very good spare part to have in the pinch.good luck .  Van
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« Reply #23 on: April 07, 2009, 08:44:19 PM »

Lin, spin the pump with a drill in a little fuel covering the pump if you can not stop the fuel with your finger it will be good or you can check it with a gauge on the out side at 65#. make sure no fuel leaks from the weap holes and you are good to go

Are you coming this way soon we will be leaving here around the 17th heading to Texas and on to Breaux Bridge for the Eagle rally and will be back May 10/12  

good luck
« Last Edit: April 07, 2009, 08:48:38 PM by luvrbus » Logged

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Dreamscape
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« Reply #24 on: April 08, 2009, 05:26:27 AM »

It's a mechanical fuel pump like the one on my 8v71 engine.  Sorry I did not mention that.

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~Paul~



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