M35A2 -good fuel to mechanical pump but dribbles from outlet?

[50shooter]

Howdy gang. I've been away and out of the game for a while, having read and searched posts for an hour, I miss this site. Long story short, my son wants to drive a deuce in the FFA event next week. Been 6 years since a deuce fired up.

1 Drained fuel and cleaned tank it was gummy shellac looking.
2 Changed all 3 fuel filters
3 Bought new in tank pump and replaced it ($$ adding up now)

Last night we turned on the switch and got good fuel flow all the way to the inlet side of the mechanical fuel pump at the IP. Determined that fuel was just tricking out the outlet side of mechanical pump, not enough pressure to climb the fuel line to the secondary and final filters.

1 The engine shutoff cable is functional and in.
2 The bleeders on secondary were open and closed and still no luck
3 I cranked the starter a couple seconds and did get the fuel to dribble faster from the outlet but still not much.

Could the mechanical pump just be gummed up like the tank and old fuel pump?
Should I try to run Acetone or something just through the pump with the in and out lines removed?
Removing it looks a bit scary to me with no gaskets, seals, knowledge on hand.

Thank you very much for any insights you may offer.

Unfortunately, the truck is in a bldg. with limited equipment and my brain is limited a bit less than our tool box.

 

[gimpyrobb]

The pump is a gear pump. Very doubtful it isnt working. If your sure though, you'll have to pull it to fix it.

 

[rustystud]

There is a pressure relief valve on the side of the pump you can remove and see if there is gunk inside. If there is and you don't clean it out you could damage the pump, possibly breaking the shaft.

 

[50shooter]

Thank you for the suggestions Gimpy & Rusty. I ended up pulling the lines from the boost pump and injecting some Acetone into it for a couple hours. I hooked the inlet hose back up and turned on the elec. pump to flush it. Worked great, Instead of the previous little dribble, fuel shot out about a foot.

Now the new problem. Truck fired right up after a second or two crank after 6 years. Idled pretty good then ran great for about 45 seconds. Then sputtered and died. Visible air bubbles in the lines between boost and secondaries. Opened the bleeder again and cleared the air. Tighten all fittings and 3 fuel filter canisters again. Same end result. Ran great for a bit, drove about 20 yards and sputtered out. More air bubbles in the same spot. Can't find a leak anyway in the system, from the fuel tank all the way to the injectors. Any thoughts? Going to keep reading threads for hints.

Thanks

 

[rustystud]

Did you change out the fuel pump hose when you replaced the pump ? They don't last forever. Remember to replace it with a submersible rated hose. Also check all the copper lines for any nicks and gouges. These could be potential leak points where the fuel is picking up air from.

 

[50shooter]

I did replace the fuel line and thought I was being smart. Now in the last couple days of reading posts to figure out my issue, I see reference to submersible hose. I'll have to order one and replace it again later.

Would it be possible that the engine is consuming fuel faster than fuel can be supplied thus causing air bubbles? It doesn't make sense in my head but wanted to ask as it could be possible there could still be some "gunk" someone in the lines from sitting and is causing a restriction. That should create a vacuum though not air in the line. To me the faster it burns fuel the mover fuel the boost pump would move and not air should be allowed in the system. Air "should" have to be coming in from a fitting, filter housing or hole in the suction supply line anywhere from the in tank hose to the boost pump.

 

[gimpyrobb]

God only knows what happened while it was sitting. If it started and ran, I wouldn't mention it but, I'd start with the fuel filters. Also might look at the fuel shut off rod and make sure it moves FREELY and the whole range of motion.

 

[dmetalmiki]

I changed EVERYTHING (including the kitchen sink!) and nothing. Despite bieng advised OVER AND OVER . Air Air Air,
They were correct.
I changed ALL and every fuel line, (throwing away the 'myriad' of t unions joints and connectors From the In tank Pump. To the filters, to the boost pump to the feul return line.
Bypassing the fuel density compensator.
Stars runs, drives like a train. (Nay, TWO trains). Good luck.

 

[dmetalmiki]

peee..ess

I just had a thunk! (same as a think but more in depth!).
DID you (per chance) NOT change that little filter/water trap under the wing? (fender). at the front of the and under the engine?. where the fuel crosses under the radiator.

 

[Floridianson]

Howdy gang. I've been away and out of the game for a while, having read and searched posts for an hour, I miss this site. Long story short, my son wants to drive a deuce in the FFA event next week. Been 6 years since a deuce fired up.
1 Drained fuel and cleaned tank it was gummy shellac looking.
2 Changed all 3 fuel filters
.

Think He did

 

[rustystud]

I normally would not suggest this. It is more a last resort kind of thing, but plug the fuel line at the tank and remove the line from the filter to the injection pump. Using a blow gun apply air to the lines. Have someone go along the lines and see if they can find a leak. It will be a small leak but you should be able to find it. It also could be the filter base gasket leaking. Either way the pressure test should find it.

 

[gimpyrobb]

Good call James, i missed that.

Id say a filter gasket is letting air in.

 

[Aussie Bloke]

G'day everyone,....

I just had a thunk! (same as a think but more in depth!).
DID you (per chance) NOT change that little filter/water trap under the wing? (fender). at the front of the and under the engine?. where the fuel crosses under the radiator.

Your talking the primary fuel filter here right?

The one at the front right corner just inside the chassis rail?



Aussie.

 

[50shooter]

You guys are awesome and a lot of good ideas for me or the next guy searching posts two years from now while his truck is causing sleepless nights. I am extremely happy to report my son got to drive the Deuce last night.

I decided we were going to start over at the beginning and test at each step. We pulled the in tank fuel pump back out and tightened the rubber fuel line fittings and the fitting that fuel line is attached to that is mounted through the fuel pump mount and attaches to the main fuel supply line. We reinstalled that and did a run test. SUCCESS on our first try!!. So the post-mortem - the air was coming from one of those two points. My advice for the guy reading this in 2024 is make sure each and every fitting and attach point is correct and tight before moving on. I thought I had done that but clearly I was wrong. Also, Air leak into the fuel system does not equal visual fuel leak.

Thanks again guys.

 

[dmetalmiki]

Roger that! Glad you had success. I should have heeded the advises given also..(Gimp and rusty (amongst others) Took "Virtual HAMMERS!" to my head before the advise finally sunk in and the NOT so obvious cure was applied.

 

[Aussie Bloke]

G'day everyone,....


Congratulations on the solution.

Now have fun with your Deuce and don't forget the pictures to share!




Aussie.

 

[50shooter]

 

[50shooter]

Can't get a photo to come up from my phone. My son has the Deuce at the FFA Barn yard zoo. Months of work and frustration paid off. Thanks all!!