HEMTT air in fuel and losing prime

[jjb]

Does anyone have a manual for the HEMTT that shows the fuel tank pickup tube? Its not in the parts manual for some reason. I suspect it may be broken. That or the check valve is bad but I don't see how the check valve would allow air in the system.

Also, does anyone know what the box is that connects to the fuel/water separator (racor) is? Its has 2 3/8" fuel lines connecting to the in and out of the racor. That is also not anywhere in the manuals. I'm wondering if that is allowing air in the system somehow?

I have replaced the fuel lines (supply and return) from the tank all the way to the fuel pump. I believe the problem is between the racor and the fuel tank as I can see air bubbles in the racor when the truck is running. Its not constant air bubbles but its pretty frequent.

 

[Gunzy]

Just pull the pick up tube from the tank and inspect it. My thoughts are it has some holes corroded into it. Another check could be to fill the fuel tank full and it the air bubbles stop that would also indicate holes in the pick up tube.

 

[jjb]

Just pull the pick up tube from the tank and inspect it. My thoughts are it has some holes corroded into it. Another check could be to fill the fuel tank full and it the air bubbles stop that would also indicate holes in the pick up tube.

I'm hoping it's the pick up tube. Do you know if I can get it out without removing the tank?

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[Gunzy]

I'm hoping it's the pick up tube. Do you know if I can get it out without removing the tank?

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I have never tried.

 

[74M35A2]

Member TedCat makes them in any length, TIG welded stainless, if you remove the original, it looks questionable, and you never want to doubt it again. Stainless tube and top threaded fitting, if it is a thread-in ordeal like on M939xx.

 

[deuceman51]

So I just dealt with this last weekend on 5 different trucks at drill as my unit has over 50 HEMTTs, typically we have found it's the check valve just outside the tank or possibly the water drain cock is stripped out as it's just plastic. Just had a truck pulling air bubbles in through the water separator. We usually just crack a line at the engine and pressurize the tank to push fuel. Check you check valve and the water separator.

 

[jjb]

So I just dealt with this last weekend on 5 different trucks at drill as my unit has over 50 HEMTTs, typically we have found it's the check valve just outside the tank or possibly the water drain cock is stripped out as it's just plastic. Just had a truck pulling air bubbles in through the water separator. We usually just crack a line at the engine and pressurize the tank to push fuel. Check you check valve and the water separator.

if it was the drain i would think it would leak. I see lots of air so it must be a big air leak?

Where do you typically see the air leaks on the separator? I replaced the gaskets, orings and filter recently.

How much pressure do you put to the tank? 5-10psi?

 

[jjb]

I just went and check the pick up tube and it looks like its in excellent shape. I reached in and tried to wiggle it but it seems sold. No evidence of rust on what I can see of it.

 

[jjb]

The check valve is leaking bad. Do you think that is my issue? The pick up tube doesn't look it can be removed.

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[deuceman51]

Most of the time it's the check valve. We use a blow gun to the tank and just try and regulate (guess the pressure the best we can). I also have a soldier up top bleeding who will yell when the fuel starts to flow where it is bleeding. I did have one where the plastic threads on the separator didn't really drip much while sitting, but would suck air in when the truck was running making bubbles. Threads must have barely been holding, but allowed air in while running. I found a bolt stuck in the drain hose by the operators and that was my first indication something wasn't right there, lol.

 

[jjb]

Most of the time it's the check valve. We use a blow gun to the tank and just try and regulate (guess the pressure the best we can). I also have a soldier up top bleeding who will yell when the fuel starts to flow where it is bleeding. I did have one where the plastic threads on the separator didn't really drip much while sitting, but would suck air in when the truck was running making bubbles. Threads must have barely been holding, but allowed air in while running. I found a bolt stuck in the drain hose by the operators and that was my first indication something wasn't right there, lol.

The check valve is aluminum and it has a big crack in it. According to the manual it's a refrigeraton valve.

The pick up tube it welded to the bung and then they welded in the bung. So if its bad it's a huge pain to fix it

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