Fuel pressure drop questions

[STIMULA8]

Hey all, I hopefully have a quick problem to address.

So I have a heavily modified wrx with an Sti swap. 2011sti shortblock, v7 Sti heads (aka 2.0) bc280 cam, Manley Pistons, gates timing kit, amrt60, tial 38mm ewg, grimmspeed up pipe, grimmspeed cross pipe, Mooreperformance DP catless, hks hi power cat back, APS fmic, APS turbo inlet, blitz bov, etc...

I will post the mods related to the problem in the FUEL system here

fuel filter under the hood (wrx) just replaced

Walbro255
Perrin v2 rails
850cc injectors top feed
Stock fuel pressure regulator
Aeromotive fp gauge

So with the car off and fuel pump primed gauge reads 42psi, on idle on a cold start my car hits 43psi, then when fully warmed up it stays a steady 40psi. I have not touched the gas pedal as this point!!!!!!

Then when I blip the throttle under the hood on the throttle body the fp gauge would drop to about 35psi. Then go back to normal. If all was functioning properly on the fuel system would the fuel pressure rise when I blip the throttle and not drop?

Car bogs also when I blip the throttle, because of the fuel pressure drop on rpm blip...

does this mean my Walbro pump is on the way out?
Should I replace the stock fpr with a new one first?

Suggestions please! Car is jumping and hesitating! ?

Thanks for reading!


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[HolyCrapItsFast]

Hmmm... it doesn't sound exactly normal... It should be less than 43 psi at an idle always because it is under vacuum... On my car it sits right around 35 psi steady at idle. The base fuel pressure should be 43 psi when manifold pressure is at atmosphere. So when you adjust the FPR, you do so with the vacuum line unhooked and plugged up. When the fuel pressure regulator is operating above atmosphere and manifold pressure is showing boost then your fuel pressure should be 43 psi plus boost.

When you blip the gas you should go from vacuum to near atmosphere so your needle should rise from idle... then upon letting go of the throttle allowing it to return to idle, you should see it go back down significantly below normal for a quick moment because vacuum is high while the engine is decelerating, then it should stabilize fast back to idle vacuum. This sounds normal and since you have very large cams, your manifold vacuum will be lower than normal so 40 psi sounds right.

The cold start has me concerned. When you take into consideration the algorithm for the fuel pump on cold start up, it should be very high at around 56 or so psi because the pump is operating at 100% duty and then after a minute or so it should drop to normal.

Not sure what to take from this but it doesn't sounds entirely correct. You could have a combination of low vacuum because of your cams and possible fuel pump issues. One thing you can do is to ensure that the fuel pressure regulator has it's own vacuum line an that there are no other devices on the same line. Beyond that I would buy a better bigger fuel pump like an aeromotive 340 or deatschwerks 300.

 

[STIMULA8]

Hmm good thoughts holy, I'm getting a significant drop when blipping, it does not rise above 40psi, and now that I took it for a drive at idle it sits at 36-38psi


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