My '03 5.9L is bogging down. Short story, I had bad batteries when the problem started. I would disconnect while at work to keep them alive to start it and get back home. Did that for two weeks, due to cash flow. Its started bogging when getting on the accelerator with medium to hard pressure. Felt just like a clogged filter. Replaced filter, no change. Popped P2509. Replaced both batteries and erased code. Problem still there but all codes are gone. Starts perfectly, idles perfectly. Checked tank module and cleaned screen, checked FCA (no code) and it passes test, new fuel filter. I think its starving but I have no codes for low pressure or anything. Could I have jacked with the ECM memory by disconnecting the battery so often? Flash ECM? Does lift pump give a code if its low pressure or fails?

 

The lift pump will not through a code if the pressure drops.The lift pump appears to be your problem, running but not supplying the fuel needed for the increased power.

Put a longer hose on the fuel filter drain. Open the drain and bump the starter but do not start. The pump will run for about 25 seconds and you should get at least 2 qts of fuel. If you get much less then the pump is not supplying the fuel needed. A fuel pressure gauge would be a better way to know what the lift pump is doing.

 

Could also be APPS.

blacksmoke

 

Sounds right.