A story of a failing rail pressure relief valve
I was towing my boat to the coast for a fishing trip. The engine was running good, until I was on an uphill passing lane going around slower traffic. By the end of the passing lane, I had lost power and was down to 50 mph. After a downhill section, normal power came back.
What could the problem be? It acted like a fuel supply issue, so I changed the fuel filters, but neither of them was particularly dirty. Next, I checked the fuel supply pressure, it was maintaining 5 psi under acceleration, but I was still losing power on hard acceleration.
I connected my scan tool to monitor rail pressure. At idle I unplugged the fuel control actuator (FCA) and saw the rail pressure jump to 22,000 psi, then drop to 11,000 psi. Test-driving the pickup showed the rail pressure dropping to 10,000 psi on hard acceleration, and never going over 15,000 psi at any time.
To verify leakage you could hook up a return line off the pressure relief valve return and verify it is bypassing fuel when it should not be. However, I was certain the fuel pressure relief valve was causing the problem, which I replaced. Then I rechecked my previous test results.
After replacing the fuel pressure relief valve I rechecked rail pressure. At idle, when the FCA was unplugged, the pressure jumped to 26,500 psi then settled at 24,800. The high rail pressure will cause a rattle and clatter, due to the excessively high rail pressure, and I shut the engine off right away. I reconnected the FCA and took it for a test drive. Rail pressure now would reach 24,000 psi on the test drive easily and would not drop until I released the throttle. Rail pressure was also much more responsive at moderate throttle. Problem Solved!