Got some strange fuel flow related noises at idle only which I only can hear from inside the car and is not always present. It sounds like cavitation / gurgling and started after I installed an 5bar FPR. Switching back to the 3.8FPR no noise....
Changed back to another 5bar FPR and the noise is back....

Hooked up a fuel pressure gauge and the readings are:
- engine off and fuel pump activated a steady 5 bar
- at idle steady around 4.7 bar
- at 3000 rpm in neutral around 5 bar
- during test drive under load/ full boost up to from 5 up to 6.3 bar

Are these readings normal and what could cause the flow noises with the 5bar FPR?

Mods are k16/24, 100 cell Europipe and tuned on a dyno 550HP/ 752NM torque.

 

The readings are normal. Sounds like a pump issue. Hows your voltage? have you checked your amp draw on your pump with both fpr? Also check you terminals for good contact.

 

The rest of the fuel system is stock?

 

This sounds like your fuel pump is getting ready to go. The 5bar causes your fuel pump to work harder.

 

Yes, the rest of fuel system is stock

 

check your terminals.... if its melted its the pump...

 

Checked the Terminals and these are ok. Just ordered a new pump and hope that this will solve my problem.

 

Solved
Got a new oem fuel pump installed and all is ok now. Got the feeling that engine runs more smooth as well in upper range under full boost. So these pumps can make cavitation / gurgling noises with a 5 bar FPR when going bad. Inspected all the hoses from the old pump and no signs of broken hoses and especially the U-hose so I suspect the electrical pump itself or maybe the in-line check valve.

 

You have gone threw 3 fuel pumps? Something isnt right.

 

No just one pump. The other thread with the guy replacing 2 pumps is not me.

 

Then yes sometimes it does go thats why people dont like 5bars it makes the fuel pump work harder.

 

Perhaps you can educate me...why does the 5bar FPR (vs. 3.8) make the pump work harder? My understanding is in higher power applications, the fuel pressure (to the rails) is potentially compromised, thus the 5bar regulator is used in order to maintain appropriate rail pressure.

 

I may be wrong but the way I understand it based on my conversation with Kevin at UMW, the function of the 5 bar is to "push" more fuel through the stock injectors. This comes at the expense of the fuel pump having to work about 20% harder which is not a huge deal. A good analogy would be someone walking around with elevated blood pressure for years which will cause their heart to work harder and shorten their life expectancy as a result. I believe Cup cars run the 5 bar stock fwiw. For my application where I drive the car at the limit for extended periods, Kevin felt that going with his injectors and enlarging the inlet of the fuel rail while retaining the factory 3.8 regulator, was a much better, more durable and safer fueling solution. This way my injector duty cycle is lowered providing a safety margin and the fuel pump does not have to work any harder to deliver more fuel. For mainly street driven cars the 5 bar is a simple and effective way to increase fuel volume.

 

Interesting, but not how I understand it...after searching on the topic:
FPR works by bleeding off a portion of the fuel flow to the injectors from the fuel pump to control the fuel pressure.

Fuel is pumped from the fuel tank to the fuel rail by the fuel pump. The FPR is normally mounted after the fuel rail to ensure that the fuel rail has priority in fuel flow. The valve in the FPR controls the amount of fuel that is bled from the fuel rail by opening an outlet port to allow fuel to flow back into the fuel tank.
All injectors need a pressure difference between the inlet and the outlet of the injector to spray fuel into the combustion chamber. This is called the base pressure.

When the pressure inside the bottom chamber of the FPR exerts a high enough force on the valve to overcome the spring force and lift the valve off its seat, it allows fuel to flow through the outlet port effectively controlling the fuel pressure in the fuel rail.

Oh and Kevin had me put the 5Bar FPR in my car...LOL

 

Kevin was going to use a 5 bar in my car but then called me and said he would feel better running a 3.8 with injectors for better fuel margins in my application so that my injectors would be running at lower duty cycles compared to the 5 bar where the injectors would be near their limits and effectively provide no "safety valve" in case of a momentary fuel pressure drop for example. He said that for track cars running all out for extended periods this would make for a safer set up compared to a street driven car which is subjected to much less frequent full throttle operation. That's the way I understand it at least..