I have an LLY and it has an Airdog 150 lift pump on it that has approximately 9 psi fuel pressure when key is on. I can crank the truck for 30 seconds and it won't build any rail pressure, if I pinch lift pump return line and get 15 psi+ it fires right up, then I can un-pinch it and truck runs and drives great. Shut it off 10 seconds, same problem. I took engine return line loose at quick connect by driver's valve cover and run in a jug, at 9 psi lift pump pressure it won't return an ounce of fuel and won't start. At 15 psi lift pump pressure it just nearly trickles into the jug while running. Also if I get it running with 15 psi and unplug lift pump it dies IMMEDIATELY! Factory fuel filter head is now bypassed since this started happening. Fuel tank also has billet sump installed on bottom. I used a piece of clear hose bypassing stock fuel filter housing and was expecting to see lots of air bubbles, but no real fuel movement like I expected to see. The pressure sensor is T'ed into the clear fuel line between FICM and fuel line fitting on passenger front of valve cover. Also with engine running and clamp removed it runs about 11-12 psi at idle and when I command rail pressure to 23,000 psi it maintains 21,500 psi, just a little short. It's an 05 LLY with 210,000 miles.
What do I check next?
What do I check next?
