T6.3544 Fuel starvation

Underway my port engine runs fine up to 1500rpm then dies from fuel starvation. I have replaced all filters, primary and final as well as the mechanical lift pump and checked all lines from the pickup in the tank to the injection pump and found no leaks. Engine still dies under load. To get it started again I have to bleed air out of the fuel lines. At the dock I have checked both the vacuum side as well as the pressure side of the lift pump and found that the lift pump will pull vac to the red zone on the raycor gauge and outputs pressure at 7psi at idle (550rpm) but drops to 0psi at 1500rpm. should there always be pressure on the output side, at all rpm's? I have bypassed the lift pump with a temporary electric pump and only loose 1psi at WOT, 23 vs 24 psi. What is going on? I have run out of ideas, any help would be GREATLY apreicated.

see if breather on tank is allowing air in above fuel level

The vent line was the first thing I checked, but worth a recheck. thanks

Still looking for an answer to my fuel question. " Should there ALWAYS be positive pressure between the lift pump and the injection pump?" If so how much? Thanks for any help.

Hi, you should have 5 to 8 lbs. Pressure. If you have 23 lbs. I believe the regulator piston is stuck or the fine mesh filter is plugged at the inlet fuel connection of the injection pump.
One other cause on some diesels is the injector sticking open causing compression to go backwards into the injection pump. The defective injector fuel line should be hot when the engine stalls.
Charlie w

Charlie, Thanks for the response. I was quite sure that the pressure should always be positive, and you have confirmed this. The 23# that I was getting was only because of the test pump that I put into the line. You gave me some other things to look at that I have not yet checked. I did not know that there was a screen filter at the injection pump other then the "spin-on" . Re your idea about the sticking injector, would a single failing injector cause all cylinders to go down or only one? Thanks again for the help.

Yes, one bad injector stuck open will send compression into the inj. Pump causing it to shut down. The filter screen is under the large nut where the inlet (fuel) connects to the inj. Pump. Also there is a pump housing pressure regulator where the fuel return line connects to the inj. Pump. If this is clogged it will cause too much pressure and shut down. Be careful removing the inlet nut to get to the screen as there are lots of springs and things to go flying. If you are confident that air is not leaking in anywhere from the tank to the lift pump and an injector is not the culprit, i suggest having the inj. Pump serviced by a pro injection shop.
Hope this is helpful.
Charlie

Charlie, Thanks again. I have performed the test to check for a missing cylinder. (Loosen each injector fuel line in turn to find which cylinder may not be firing - all seemed to be OK). I will check all the items that you noted before I remove the injection pump. I suspect that this a major issue and big bucks to have repaired.

Just in case there is a blockage in the fuel return line try disconnecting the line at the nearest connector and put it into a bucket--run it up and see if it stalls.
Most shops will want to rebuild the pump (approx $300.- $500.) if the housing pressure reg is bad about $60. If the inlet pressure reg is stuck or dirty filter screen about 30 minutes labor
charlie w .