04 Columbia Fuel System?

I am working on a 04 Columbia with a OM460, which I believe is the same as a MBE 4000. The truck died on the driver, he said it acted like it ran out of fuel. Both tanks are full and valves are on.

First thing I noticed is there is a lot of bubbles/fuel burbling around in both tanks when trying to start it. So I figured it was sucking air before the pump. I then made a test line to a 5gal can and hooked it directly to the port that goes into the Ecu. Which is after the water separater. After priming it and hitting it with some ether/wd-40 I got the truck started and running fine. Still bubbling like crazy in the tanks, while running from the test tank I hooked up. So that eliminates everything from the pump bank. Next I hooked it back up normal. Pulled the canister filter, while I was there I made sure the valve in the bottom was not leaking. I pulled the return line off to verify that. It seemed fine. Made sure filter was seated good.Put everything back together got it started again. Still bubbling. Let it run for an hour or so at 1k rpm. It sit overnight and lost its prime. Pulled plastic covers off side of engine. No obvious leaks anywhere, so I pulled the check valve out of the back of the engine. It was clean and operating fine. So next I pulled the return line back off the filter base, and breifly turned the motor over. When I hooked it back up I heard the pressure rush back to the tanks and it gurgled for a few sec.

I have no clue what the problem is. Any ideas? Its obviously sucking air somewhere I just have no clue how. It shouldn't suck air anywhere after the pump correct?

 

No the fuel filters wasn't changed before the problem. I also checked to make sure the canister filter was seated.

I believe about 3 months before the issue, this truck had head gaskets and a egr cooler installed. Which shouldn't be related correct? And I don't believe it was driven more than 1000 miles in that 3 months.

 

I havn't pressurized the tank. But I am pretty sure it isn't sucking air before the pump. Because of the test tank I installed going directly into the Ecu on the engine. I also don't think it would prime up and run if it was sucking that much air pre pump?

Would a injector being loose or a bad cup cause back pressure into the system? I am guessing it could back feed pressure through it's individual high pressure pump into the low pressure side. In turn blasting the check valve open?

I know I can make sure the injectors are tight, but how should I go about testing them? Short of pulling them out and getting them to a injector shop.

Thanks for the advice. Please keep any ideas coming.

 

Ok I do appreciate it.

 

Thank you for the diagrams. They are more detailed than the one I have.

But I am still hung up on how that much air is entering the tank. And still allowing the truck to run. This may sound stupid, but is there a way or do I need to bleed the fuel return line?