You dont have to delete the pprv to install a focus pump. its a direct fit. A little more detail to what the PPRV does and what happens when you remove it.
The most simple explanation of the PPRV is a check valve. ALL cars have some sort of PPRV device. Without one all fuel injection cars would be extremely hard to start because they wouldn not maintain any fuel pressure after the prime cycle had ended
The PPRV allows the pump to turn on for a short time to prime the fuel system at start up. When the pump shuts off what holds the pressure? The PPRV. The PPRV on some models also blows off excessive pressure. We're talking when its above 60 or 80 lbs.
What does the PPRV cause hesitation? - picture this. Your hammer down balls out near redline and the fuel pump is running wide open then suddenly you lift and the throttle shuts. What happens? The fuel pressure spikes, the ecu registers this at the FRPS and slows/shuts the pump down but the PPRV holds the line pressure way above the setpoint. As the pump slows down there is nothing to relieve the pressure so the pump continues to slow down thinking the pressure isnt dropping... because the pprv is holding all of the fuel pressure on the sensor. This all happens within a split second of doing a gear change. Now you hammer down and the car falls on its face for a split second. Why? because the ECU thinks there is excessive fuel pressure so the pump slows WAY down and the PPRV holds all the line pressure when your foots is off the throttle. When you hammer down the pump is not running near the capacity needed and there is an IMMEDIATE pressure drop. The car runs out of fuel for a split second and falls on its face. The ECU registers this and sets the pump into wide open to make fuel pressure. The power comes back and all is happy until the next gear change.
Why do only some cars have this problem? It relates to HP being made and how hard the fuel pump is running. If the fuel pump is not running as fast it doesnt spike as hard. The spike isnt as extreme so the ECU response isnt as extreme and there isnt as much pressure drop. This is why mostly 03/04 cobra guys rave about the issue with 400+HP and not bolt on GTs.
Why does removing the PPRV stop the hesitation? When you lift and the fuel pump slows down without the PPRV FUEL IS ALLOWED TO BACKFLOW THROUGH THE PUMP. This reduces line pressure and the fuel pump response isnt as dramatic so the fuel pump continues to run at a higher duty cycle instead of just basically shutting down. Now when you hammer down the pressure hasnt dropped as far because now that fuel is allowed to flow both directions the ECU can properly control the fuel pressure even when the motor isnt consuming hardly any after a WOT gear change.... which means the pump doesnt shut down.
With the PPRV inline pressure spikes and the PPRV HOLDS THE PRESSURE. It can be as high as 90psi. So the ECU freaks out and practically stops the pump. With the PPRV gone the spike isnt as high... the PID fuel pump controls dont slow the pump down as much and you dont have the dramatic pressure drop when back on the throttle.
This is alot to take in and I honestly have a hard time explaining it so that everyone will understand. Not all of this is exactly correct but it will help it make sense to you. If your interested as to why the pump reacts more or less with different pressures I can go into PID controls loops but hold onto your seat. I hope i didnt make this too complicated or ramble too much.
1999 GT 630rwhp on pump, TFS Heads, MMR 4.75L, Highly Modified Kenne Bell 2.1 @ 20lbs, Custom Intercooler, JLT High Boost CAI, CMS Custom TFS Specific Cams, 3.55s, MGW, T56