M35A2 Fuel Related Issues

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jrnekos

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Hey there everyone,

First time poster here. Hope all of you are staying safe with everything going on right now. This will probably be a longer post as I want to give as much info as possible.

Bit of backstory -
I’ve always wanted an M35A2, I finally found one that was the right price with the setup I was looking for. Everything looked great, started and ran no problem after sitting in the cold for a few days. Checked all fluids, added some diesel and made my way home. I got about half way home (Home being near New Paltz, New York) and I was pulling off to a rest stop when the truck just died on me. First thought - “Did I run her outta fuel??” The answer was no. Had about half a tank of diesel left. Long story short, I could not get her going again so I had it towed home. Jumping forward a few days I was checking over the fuel system and I noticed I could not hear the in tank pump running so just out of curiosity I cracked the main fuel line coming from the pump it was bone dry. Pulled the pump out and it was clearly a bit messed up. The rubber line that is part of the pump was ripped in a spot and the pump itself has definitely seen better days.

Now for the situation at hand -
After replacing the pump and changing all fuel filters I seem to not be getting any fuel. I triple checked and the pump is working great pushing fuel through the line up until the first filter. I used the bleeder on the bracket for the secondary and final filters to attempt to get the air out of the lines but I never had any fuel come from the bleeder. I was going to check the petcock on the primary filter to see if there was fuel in it, but a previous owner snapped it off. Before I go digging into the truck, is there anything basic I should double check first? This is my first interaction with a Deuce so maybe I am just missing something simple. I did notice the filter that came out of the primary filter housing was much longer (I am assuming that’s for water separation) in comparison to the filter I installed. I used the spring and such to make sure the new filter was sitting properly but maybe I messed something up there? I wanted to get some outside opinions before I head over to work on it again as it sits about 30 mins from my house. Any tips, tricks and whatever else is greatly appreciated!

Again, sorry about the long post but I figured a first time post should be somewhat thorough.

Thank you all,
Justin
 

Elk1111

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Open the bleeder to the second set of filters and put some air to the fuel tank. Assuming nothing is clogged you should get fuel coming out of the petcock.
 

cattlerepairman

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You seem to have a good step-by-step mindset already.
You can put a pressure gauge into the plugged port where the fuel lines comes up on top of the tank. With the in-tank pump running, you should see 5-7 psi there.
Loosening the fitting and removing the fuel line on top of the tank, removing the lines at the filters (some use the bleeding ports; whatever) and blowing the lines through with compressed air is a good suggestion Generally, I like to do that in segments and prefer to blow crud backwards towards the open fuel line on top of the tank, but I am sure different ways of doing this will work.

Elk1111's way may work, however I do not like blowing stuff forward from the primary to the secondary filters because there is a booster pump in between and you do not want this pump to eat all the muck you might be sending its way! Blow stuff backwards from the secondaries.

If you put a pressure gauge on the port at the secondary filters, you should see 10-ish psi when cranking and 20 plus (up to 60?) when idling.

I quickly looked through the troubleshooting manual TM9-2320-20-2-1 organizational level troubleshooting and it does not add much to what was already said.
 
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Elk1111

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I was just thinking he was loosing prime between the primary and secondary filters maybe due to a weak lift pump. The air to the tank was to pressure the system and get any air pockets out of the lines. Have soldier B shut off the petcock as soon as you get a steady flow of fuel coming out of the petcock.
 

jrnekos

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You seem to have a good step-by-step mindset already.
You can put a pressure gauge into the plugged port where the fuel lines comes up on top of the tank. With the in-tank pump running, you should see 5-7 psi there.
Loosening the fitting and removing the fuel line on top of the tank, removing the lines at the filters (some use the bleeding ports; whatever) and blowing the lines through with compressed air is a good suggestion Generally, I like to do that in segments and prefer to blow crud backwards towards the open fuel line on top of the tank, but I am sure different ways of doing this will work.

Elk1111's way may work, however I do not like blowing stuff forward from the primary to the secondary filters because there is a booster pump in between and you do not want this pump to eat all the muck you might be sending its way! Blow stuff backwards from the secondaries.

If you put a pressure gauge on the port at the secondary filters, you should see 10-ish psi when cranking and 20 plus (up to 60?) when idling.

I quickly looked through the troubleshooting manual TM9-2320-20-2-1 organizational level troubleshooting and it does not add much to what was already said.

Very sorry about the delayed response, work was pretty packed this week. I am heading over to work on the truck either Saturday or Sunday and I will report back with anything I find. I am going to go section by section and make sure all of the fuel lines are clear and usable. Once I know they are good to go, I am going to see where I am getting fuel up to and start working off that. Would that booster pump possibly stop fuel from passing through? Is there anything else I should double check while I'm at it? I am pretty mechanically inclined but again this is my first time ever working with one of these trucks so I wanted to gather some external opinions before proceeding.


Open the bleeder to the second set of filters and put some air to the fuel tank. Assuming nothing is clogged you should get fuel coming out of the petcock.
When you say put air to the fuel tank, I am assuming you are talking about throwing a fitting on the tank and hooking up a compressor?


Thanks again,
Justin
 

Elk1111

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Yes. You don’t need much pressure. 20-25 pounds. You just need to push the fuel up to the secondary filters. As Cattle said, it would be a good idea to clean the lines out first though.
Once you get all of the air out of the lines by priming everything via pressure even a weak lift pump will still work.
If you don’t want to install an air connection just use a plastic bag and your hand to seal the tank opening around your air hose. You will just need another person to close the bleader once you have steady fuel coming out.
 

Floridianson

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Forget the air to the fuel tank you said your in tank pump is working and getting fuel to the primary. Now check to see if the copper tube that runs from the primary to the booster pump under the frame rail is crushed. If that is ok then remove the line at the Injection booster and see if you have fuel there. You might have a obstruction just before the fuel enters the IP booster pump. If that is clear and you have good fuel to there then move to the secondary fuel filter. Then the bleed screw between the secondary fuel filter. If good disconnect fuel line to IP Head and see if you have any fuel going to the head. The in tank pump will remove all air if the lines are cleared of any obstruction. If you must put air in the system as someone else said open the feed line from the tank and push air backwards out of any lines not forward. If the obstruction was at the IP booster pump you do not want to push it through the booster but back out.
 
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M37M35

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You don’t need much pressure. 20-25 pounds.
DO NOT put that much pressure to the fuel tank!!!!! It will bulge or rupture with that much pressure!!! 3-5 psi is plenty to push fuel through the lines.
just use a plastic bag and your hand to seal the tank opening around your air hose.
This is a better way of doing it. Makes it harder to apply too much pressure.
 

jrnekos

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Alright so here’s where we are at. I have fuel up at the secondary and final filter, but only the secondary filter has fuel in it, not the final. When I cracked the line that comes from the booster pump, the fuel comes out but very very slowly. I’m clearing the lines out as we speak and we will see what happens. Will post an update once done.


Sent from my iPhone using Tapatalk
 

jrnekos

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Update -

Have fuel coming from the tank, through the first filter up until the mechanical booster pump. Clean and well pressurized fuel. The line going from the booster to the secondary and final filter has little to no fuel coming through it. (It dribbles out.) The secondary filter had about 2-3 inches of fuel in it. The final filter was bone dry. When cranking the engine, the fuel line after the booster pump had a bit more fuel but it still seemed less than it should be.

I know the fuel up to the booster pump is good and has good pressure too. (Did not pressure test it, but it seems to be more than enough.) Is there a possibility of the booster pump being clogged up with stuff? How would I go about cleaning that?

Thank you,
Justin
 

Floridianson

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If we believe booster has a restriction then I might remove the rubber line that comes off the booster at the copper cross over fuel line. Remove line from booster to secondary and apply low pressure air blowing back through the booster and out the rubber line. The booster IP is a pain to remove so maybe try back flow low pressure air.
That booster pump is such a pain to remove I rather be kicked in the chestnuts four times, have a bad case of hemorrhoids and two root canal's.
On a side note are you sure you primary filter is working as it should with all correct parts and pieces? It should have stopped most large enough stuff that would have clogged the booster.
 
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M37M35

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If we believe booster has a restriction then I might remove the rubber line that comes off the booster at the copper cross over fuel line. Remove line from booster to secondary and apply low pressure air blowing back through the booster and out the rubber line. The booster IP is a pain to remove so maybe try back flow low pressure air.
That booster pump is such a pain to remove I rather be kicked in the chestnuts four times, have a bad case of hemorrhoids and two root canal's.
On a side note are you sure you primary filter is working as it should with all correct parts and pieces? It should have stopped most large enough stuff that would have clogged the booster.
It's been a couple years since I replaced the seals in my booster pump, but I 'think' I remember there being a check valve/bypass valve in it. (someone correct me if I'm wrong here). It would make sense cause the booster pump is a gear pump and the in-tank pump wouldn't be able to flow fuel through it if there wasn't a bypass/check valve. That would say you couldn't blow air/fuel backwards through it. But if it's stuck, then some low pressure air blown forwards might unstick it...
 

Floridianson

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It's been a couple years since I replaced the seals in my booster pump, but I 'think' I remember there being a check valve/bypass valve in it. (someone correct me if I'm wrong here). It would make sense cause the booster pump is a gear pump and the in-tank pump wouldn't be able to flow fuel through it if there wasn't a bypass/check valve. That would say you couldn't blow air/fuel backwards through it. But if it's stuck, then some low pressure air blown forwards might unstick it...
I can not explain why fuel will go around the gear pump but it will. That is why we can with the engine off and just the in tank pump running test for pressure or bleed air after the booster on the bleed screw. So yes I believe it will back flow. The tm says it starts to open at 60 psi but as said 4 to 7 pounds can be seen at the bleeder engine off. Also with just the in tank pump running it will circulate fuel back to the fuel tank. That also tells me fuel will pass through the booster engine off.
 

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Floridianson

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No have not played with my Deuce or it's fuel system in quite a while is it in a TM? I would still think it would be better to push what ever is blocking the booster back the way it came not through it some how.
 
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jrnekos

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If we believe booster has a restriction then I might remove the rubber line that comes off the booster at the copper cross over fuel line. Remove line from booster to secondary and apply low pressure air blowing back through the booster and out the rubber line. The booster IP is a pain to remove so maybe try back flow low pressure air.
That booster pump is such a pain to remove I rather be kicked in the chestnuts four times, have a bad case of hemorrhoids and two root canal's.
On a side note are you sure you primary filter is working as it should with all correct parts and pieces? It should have stopped most large enough stuff that would have clogged the booster.
I should have added in my previous post, I did attempt to back flow the booster with some air. I had fuel come out, but once all put together the fuel will still not pass through the booster unless cranking and even then it would come out with barely any pressure. I genuinely do not think the fuel filters were changed in the past quarter-century, so who knows what actually got past the primary. All of the filters were absolutely disgusting.

It's been a couple years since I replaced the seals in my booster pump, but I 'think' I remember there being a check valve/bypass valve in it. (someone correct me if I'm wrong here). It would make sense cause the booster pump is a gear pump and the in-tank pump wouldn't be able to flow fuel through it if there wasn't a bypass/check valve. That would say you couldn't blow air/fuel backwards through it. But if it's stuck, then some low pressure air blown forwards might unstick it...
At this point, I am going to attempt to put some air through it the right way just to see if we get anything freed up in there. Will report back if I get somewhere. Just a side question, what would be the best way to clean out the fuel tank of rust? I used a magnet to pickup the large chunks but I can tell there is a lot more to be cleaned out.

Thanks everyone for the responses,
Justin
 
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