M923a2 fuel issue. runs and dies, runs and dies.

[Marc23760]

Thanks in advance to all that read this.

I bought a 1990 (I think) M923a2 5 ton cargo truck about 3 weeks ago. It was poorly serviced when I received it. I have changed all filters etc with the exception of the fuel system and the driveline. ( I know I shouldn't have waited on the fuel system).

For the past week I have been driving it every day. Ihave ran about 70 gallons of fuel through it and the other day coming home The truck died after starving for fuel.

Fighting with it for several hours I managed to bypass the cartridge filter due to the large amounts of rust and garbage in it. I still couldn't get it started so I changed the filter mounted on the engine and put a primer bulb in line to push fuel. I finally got it started and home which was luckily only a quarter mile away.

Now the frustration of not having a solution:

It Will run and only run for a few minutes then will stall out starving for fuel. I bleed it up to the bleeder just after the lift pump and am able to restart again only to have it run for only a few minutes, again.

This is just keeps happening over and over. Last night I walked away from it. Today I completely cleaned the canister, all lines and brake cleaned everything. Changed both filters and put the truck back in the stock configuration.

i still am stuck with the same problem. When I bleed the lines I feel as though the fuel coming out is frothy. It never comes out as a steady stream. I thought lift pump was bad or drawing air so I replaced it. Even when it's running and I crack the bleeder it's still foaming with what appears is air.

it turns out it's not the lift pump. My next move is to run it directly out of a diesel can and see if I can bleed it clear and clean. If it stays running (or if it doesn't) I am going to put a wheel valve on the fuel cap and pressurize the tank.

The only thing I can Think is, I am sucking air from a cracked fuel line or a damaged pickup in the tank ??

ive had several diesels and i know this has to be simple but I had to walk away from it again tonight. It's driving me crazy and I cannot figure out where the air is coming from.

Im up for any suggestions I know a lot of guys have had this issue.

 

[Rmtaunton]

Bingo , Bad fuel line or pick up in tank its , common for these trucks as they have sat for a long time

Good luck

 

[98G]

Bingo , Bad fuel line or pick up in tank its , common for these trucks as they have sat for a long time

Good luck

This. Replace all your rubber fuel lines and that should resolve it.

Check your filter gaskets too, but I presume you did this already...

 

[allie]

I'm having same issue with my m931. Only thing I did recently was cut out a bad area of fuel line and replaced it with a rubber 3/8 hose with hose clamps. I'm also wondering if I'm sucking air. Gonna first replace fuel filter and clean out the housing. We'll see from there.

 

[Marc23760]

Thanks for the quick responses guys. I have been researching some More and i now have more motivation to go right for the fuel tank in the morning. I have a gut feeling the joint at the top of the pickup is the culprit.
If it is the worst I did was spend $76 and an hour and 45 minute round trip to diesel injection for a un-needed lift pump.

I am hoping for a Lesson learned in the am.

 

[Marc23760]

It ended up being the "reversed" flared fitting that goes into the 90 degree elbow into the tank on the end of the fuel line. If anyone can learn from this common mistake, take the time to pressurize your tank, it will save loads of time trouble shooting.

What is particularly strange is the fitting that I see normally going bad at the top of the pickup was totally sealed and in good condition.

I ended up deleting the entire old pickup and all the fuel lines to the canister filter due to all the old fittings.

 

[M35A2-AZ]

My M923A1 had the same problem with the tank. Glad you found it.
http://www.steelsoldiers.com/showthread.php?79327-M923A1-losing-prime&highlight=fuel+tank

 

[TedCat]

I am replacing fuel lines due to age, algae contamination and prior owner involvment. Can you share any drtails abiut the pickup you put together? Looks great.

 

[Marc23760]

I had a tubes a hoses guy whom does hydraulic lines make the lines for me out of Hyrdo lines for no chance of a leak. I also had him make the pickup out of stainless steel. You'll need to find a shop that is set up to build this but its well worth it. Because your fuel pickup will eventually fail...