This is my first post so forgive me if I break any rules.

Thanks for all the wisdom in here. I've read every post very carefully a number of times. I think almost everyone on here is correct. I think there are multiple problems that all have exactly the same symptom and I think that it's just a significant amount of detective work and a little bit of luck required to get to the answer.

As I see it the symptom that everyone observes is low fuel pressure at the injector/fuel rail.

Low fuel pressure at the rail has three main causes.
1. Faulty High Pressure fuel pump
a. Low Hydraulic Fluid in pump Issue
b. Fuel Pressure Solenoid O-ring deterioration
c. Fuel Pressure Solenoid Coil deterioration
2. Fuel Delivery Restriction
a. Fuel filter clogged
b. Other fuel line / Passage restriction
3. Faulty Low Pressure Fuel Pump.
a. Damaged Pump
b. Fuel Relay connection point damage (JBE Module)

There may be other issues but these are the issues that I'm aware of.

I am rebuilding a vehicle that had overheated and blew a head gasket. I've never seen it run normally so don't know what issues it had prior to my possession.
My low pressure fuel pump died outright so I had to change it to even try to start my car once I got the engine back together.

Once I changed out my low pressure fuel pump, I was able to start my car and it ran fine and performed as normal until the engine temp reached about 180 degrees F. At this point it started to falter on wide open throttle.

Due to the fact that the car had sat for a significant amount of time, I thought it would be wise to change the fuel filter to eliminate that as a possible cause. I did this.

The issue still existed. Since I had changed the LP fuel pump and fuel filter, I turned my attention to the HP fuel pump. The depth of my temp compensation piston was at 22mm and I thought it might be on the edge so I refilled it with hydraulic fluid and brought it back well within tolerance.

The problem persisted so I pulled the fuel pressure solenoid on the pump in hopes that it would be something as simple as the solenoid O-rings. The O-rings were in perfect condition. They were nice and pliable and appeared to have no damage.

I figured the ONLY thing that could be an issue was the solenoid on the HPFP so I purchased a brand new one. I replaced it today and am having the EXACT SAME ISSUE.

I drove it until my car heated up to 180 degrees F and the problem started like before. I parked my car, let it "cool down" for 10 minutes and started it again. This time although the temperature of the engine was 215 degrees F, it ran fine for a few minutes. After about 2 minutes, it started doing it again.

I'm 99.9% sure it's been the solder joint on the fuel relay the entire time. I think that the time for the coil (amp draw) on the fuel relay to heat the solder joint up on the board is the same time required for the engine to bring the coolant up to temp. If the heat of the engine is a factor in the loss of fuel pressure, once it was at 215 degrees F the fault would be constant.

Because the 10 minutes I turned it off would be sufficient to cool down the JBE board it worked as normal until the heat from the coil (amp draw) heated up the bad solder connection again.

Sorry for a long post but I though my troubleshooting and explanation might help someone else.

 

I'm definitely chasing a similar issue with a 2009 R56S........The car would start rough and start shaking very erratically after
a few minutes it would smooth out and throw the check engine light on......checked with mini scanner...
fuel rail pressure low......High pressure fuel pump.......pressure to high and a few other codes I'll add the codes when I scan the
vehicle again.....