Hey all,

I've put my fuel pressure gauge on the truck and tried to get her to idle the best I can.

With the vacuum line on the fuel pressure regulator, my vacuum gauge needle bounces around constantly between 50-55psi. If I remove the vacuum line, the needle stays pinned at 55psi. This happens regardless of whether or not I have the vacuum line covered with my finger.

Is my FPR bad? I read a thread that said if your oil is dirty after a change and much higher than the fill line, it's possible the FPR is bad and is dumping too much fuel into the cylinders, causing rough idle and allowing fuel to leak into the crankcase.

Does this sound true? I'm trying to diagnose a rough idle and and want to make sure the FPR is working properly.

Thanks!

 

Is the needle fluctuating from 50-55 or oscillating? Fuel pressure should increase 5 psi when you remove vacuum line from FPR.

Needle oscillation is common on non-fluid gauges. But if fluctuating then, you may have problem. I would change fuel filter, but I think you just replaced tanks and pumps. If filter was ran with any trash, I would replace or inspect for good flow. Other possibility is clogged injector screens.

 

Basically, when the gauge is hooked up and the vacuum line is attached to the FPR, the needle moves rapidly between 50 and 55 psi. It doesn't hold a steady pressure. When I remove the vacuum line on the FPR, the needle stops moving and settles at 55 psi. I can't really tell if that's a jump of 5 psi or not. And the psi remains constant, regardless of RPM.

The gauge is air-filled. Fuel filter is new, but replaced before I did the tanks. And you're correct; both tanks and FDMs are new.

I also pulled the injectors and ran pure seafoam through them.