M929A2 Fuel Tank Selector

[8543BOB]

Good morning,
This question may seem basic, but I want to make sure. when the selector handle is rotated all the way clockwise I am feeding off the passenger side tank, correct? and counterclockwise, the driver side tank? The reason I ask: I have to bleed the injector pump after shutdown and it sits for 15 to 20 minutes. I am trying to troubleshoot the air leak. I am going to feed the lift pump from a separate fuel container; bypassing the selector valve. we will see
Thanks
BOB

 

[jcappeljr]

I have a m931 that does the same thing,Its loosing its prime somewere.

 

[smittyjr355]

Almost all the M931 and M929 trucks I have had needed the rubber hoses replaced that go to the selector valve. This is where I would start if you have a prime issue. Usually pressurizing the fuel tank with air will show the leaking lines, but not always.

 

[dilligaf13]

Ditto

 

[M35A2-AZ]

Ditto, On the hoses, but all the way clockwise is the drivers side tank and counter clockwise is the passenger side.
There should be a data plate on the floor that is marked the tanks.

 

[gottaluvit]

Ditto, On the hoses, but all the way clockwise is the drivers side tank and counter clockwise is the passenger side.
There should be a data plate on the floor that is marked the tanks.

Thank you for verifying this. I was bewildered one day when I pulled into a station thinking my passenger tank was down only to find it full. My data plate is faded so I just assumed pointing the valve lever in the right direction should do it. It had me thinking the guage selector wires were crossed as I had to replace that.

I too, had one tank that wouldn't let the truck run only to find out the hoses were crossed on the selector valve by some private, I assume. I found a nice picture of the hose configuration in a thread that shows a teardown and cleaning of the valve.

 

[Andyrv6av8r]

My 932A2 was losing prime also. So, like everyone else, I assumed that the selector valve needed rebuilding or hoses needed replacing. I replaced the o-rings in the selector which was easy and actually looked very good inside. I figured while I had the fuel system down that I'd go ahead and replace the main fuel filter located inside the left front wheel well. And this is where it gets interesting. After taking the canister apart, I noticed that there were 2 small o-rings down in the bottom of the can. I recognized these as the ones that fit underneath the square washer on the thru-bolt. Upon closer examination of the bolt, I didn't find the o-ring in place. I believe that soldier A or B or their cohorts thought the o-ring went on after the bolt was dropped in from the top bracket, then the filter canister went in place. I reassembled with a new o-ring under the bolt head, bled the air and the truck has run flawlessly on both tanks ever since.


Moral of the story is: make sure the o-ring, item 4, is in the proper place on your filter canister or you will continue to lose prime.


As a side note, I noticed after fixing this issue that you can actually hear and feel the lift pump pumping as you touch the selector lever and I couldn't before the fix. It has a very distinct " thump " to it if it is pumping with no air leaks in the system.

 

[8543BOB]

Hi all and thanks for all the feed back. I ran the 929 a2 off a separate fuel supply; I piped into the inlet side of the lift pump, bled the injector pump, started right up. let it run for 5 - 10 minutes, shut it down for an hour. stared right up. so my air leak is between the lift pump and the selector valve. I think i'll by-pass the selector valve and see what I get. keep those cards and letters coming, again thanks
bob

 

[gottaluvit]

Hi all and thanks for all the feed back. I ran the 929 a2 off a separate fuel supply; I piped into the inlet side of the lift pump, bled the injector pump, started right up. let it run for 5 - 10 minutes, shut it down for an hour. stared right up. so my air leak is between the lift pump and the selector valve. I think i'll by-pass the selector valve and see what I get. keep those cards and letters coming, again thanks
bob

The canister filter is between the tank selector and the lift pump.

 

[8543BOB]

Good evening, here is what I got today; with the fuel selector turned all the way clockwise she starts and hold her prime for over a day, drivers side tank. Selector counterclockwise, passenger tank, she will run, but after shut down she loses her prime in 15 minutes. So I figure it to be the hose from the selector to the line that feeds the primary filter. But at least I can drive her, park her and come back in an hour and I know she will start. Thanks again for all the input.
BOB

 

[gottaluvit]

Good evening, here is what I got today; with the fuel selector turned all the way clockwise she starts and hold her prime for over a day, drivers side tank. Selector counterclockwise, passenger tank, she will run, but after shut down she loses her prime in 15 minutes. So I figure it to be the hose from the selector to the line that feeds the primary filter. But at least I can drive her, park her and come back in an hour and I know she will start. Thanks again for all the input.
BOB

I would name the line from the passenger tank to the selector as my primary suspect. If the driver's tank works good than you must be good from the selector all the way to the lift pump or either tank should lose the prime equally.

 

[8543BOB]

Good thinking. I will probably not get back to it till after thanksgiving. Thanks bob

 

[gottaluvit]

It is frustrating but you will figure it out and then celebrate!

 

[tomtwigg]

Does anyone have a detailed port diagram for the fuel selector valve?

 

[simp5782]

Does anyone have a detailed port diagram for the fuel selector valve?

best I can come up with from the parts TM

Also this thread is helpful https://www.steelsoldiers.com/showthread.php?76086-5-ton-fuel-tank-selector-valve-cleaning-rebuild

 

[cwedge411]

is the 8 series much different?

 

[simp5782]

is the 8 series much different?

I know the valves are all the same. Should be the same line connections I would think.

 

[tomtwigg]

Thx for the info on the fuel selector valve

So far I have replaced the hoses to the valve, still no fuel from the drivers tank

I removed the fuel line to the tank and no restrictions

Does anyone have a diagram of the fuel selector vale?

 

[162tcat]

Thx for the info on the fuel selector valve

So far I have replaced the hoses to the valve, still no fuel from the drivers tank

I removed the fuel line to the tank and no restrictions

Does anyone have a diagram of the fuel selector vale?

Can you elaborate? Is it sucking air? It's a very simple setup. 3 supply ports and 3 return ports. Has it ever worked? Give us some info to help diagnose this.


Sent from my iPhone using Tapatalk

 

[simp5782]

Thx for the info on the fuel selector valve

So far I have replaced the hoses to the valve, still no fuel from the drivers tank

I removed the fuel line to the tank and no restrictions

Does anyone have a diagram of the fuel selector vale?

Make sure the pickup in the tank isn't broken off or cracked. This will cause a no flow problem.