2006 Volvo S40 2.4i

So my car is acting up once again.

Code P0305 - Cylinder 5 misfire (new spark plugs and already tried switching coil packs to determine if that was it, but it was not. same code came back on.)

Dry Compression test on cylinders 1-4 was ~150psi.
Cylinder 5 was ~120psi.

The car does not start on first try. The fuel pressure (using a gauge) only goes up to like 10psi with the first key turn to on. Then I take it out and do it again to prime the fuel pump again and it goes up another 5-10ish. After a few of these I can get it up to 40psi. But it won't go any further than that.

I start the car and it is a little hesitant to catch and stay on, but it does. The pressure is now at 55psi (the spec that it should be at). When I turn the car off it goes back down to 40psi.

So with the pressure at 40psi with the car just turned off, I watched the gauge and it dropped 2 psi in a minute or two then slowly dropped to 30psi over the next ~30 min.

The fuel pressure regulator I guess is part of the fuel pump, so my only thought is that I have to replace the fuel pump. But I wanted to get a second opinion of it before I go through my time and money fixing something that may not be the problem.

Anyone's 2 cents on this?


**Update

I'm thinking I have 2 problems. One the fuel pump. That would explain the lack of fuel pressure before starting and also the sudden drop to 40psi after turning it off.

The second problem being, a leaky injector (hopefully) or maybe a valve problem causing the misfire.

 

Anyone?

 

There is no fuel pressure regulator on the newer models like there is on the older 2000-2004 models. The newer models use variable voltage through a fuel pressure sensor to vary the voltage to the fuel pump. Normally you will get a warning message about being "down on power" or similar. This is the clue to look at the fuel pressure sensor. It is located on the end of the fuel rail on the passenger side. In this pic it's just in front and below the oil fill cap.