By now it should be apparent to anyone with even a passing interest in the mechanical workings of a vehicle that a lot of the time the smallest things can cause the biggest problems. That’s certainly the case with this month’s focus: the fuel pressure regulator on a 2005 LLY Duramax.
As the name plainly states, the FPR regulates the pressure of the fuel flowing through your system. It manages how much fuel to send to the engine for different actions, so it’s constantly working. The symptoms of a bad regulator usually manifest as a surge when idling, though sometimes the surge can happen at speed while driving. Other symptoms include power loss on acceleration or hard starting. Sometimes it can get bad enough to force the truck into limp mode with a low rail pressure warning.