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PPRV cutaway
- Thread starter Aaron175617
- Start date
those pics are really small it's hard to see what your talking about?
I clicked on them and they got bigger. Pretty interesting. Why in the world would they put that in a fuel line?
It's designed to open when it sees about 67 psi and does it most of the time with no problems, but not reseating after blowing-off IS the most common failure of the part.
If it fails, you'll know it......Car wlll crank longer before it starts as there won't be residual pressure maintained in the line.
:burnout:
Here is my take on the subject.
http://www.svtperformance.com/forums/engine-tuning-214/281209-frps-6.html#post7581013
Using Aaron175617's images.....
Here is what happens when things are running normal.
Pumps are pumping, fuel is being used at a reasonable rate, little bit is being dripped back into the tank through the small nipple, and the flow is going through the larger, straight shot valve.
Something has caused a pressure spike. Normally, the pumps running hard during a WOT, high RPM run and the throttle body shuts closed. ECU reacts by significantly reducing the duty cycle of the fuel injectors. Pumps keep pumping, pressure spikes through the system, and the ECU hasn't reacted. Fuel is still going through the straight shot valve and more is leaking though the small nipple due to increased pressure. Because the pumps are still creating pressure, that pressure is being applied to the side valve keeping it shut.
Computer basically goes 'oh crap!' and needs to bring fuel pressure down by cutting the pumps. As the pumps are reducing speed and pressure on the pump side of the PPRV is reduced, fuel flow doesn't pass through the straight shot valve. Instead, it pushes open the relief valve on the side and passed back through the pumps. Any pressure between the pumps and PPRV will also have some fuel come out of the small nipple.
The ECU has WAY over reacted and shut down the pumps completely in an effort to get fuel pressure under control. Cars with bad hesitation issues will actually see 0psi if they datalog. Problem is that the spring holding the side valve is designed to maintain about 67psi. Pressure will only be reduced further through the injectors. You can't really see a steady ~67psi cause the injectors are always working and reducing pressure in the system between. If the PPRV was used in a controlled environment, you'll see it holds 67psi +/-7psi.
Why they designed it that way, I have no idea. I'd like to pick the engineer's brain on that one.
I would have done something like this....
Block off the chamber between the inlet and small nipple so no fuel can pass. Open up the small nipple hole to allow a lot more fuel to pass. Set the spring pressure so that fuel pressure can be raised to 39psi (delta) plus actual boost (say 20-25psi). That means it'll blow off at roughly 59 - 64 psi. Setting it up that way might also help FRPS damages. Only down side I see is that if the side valve were to fail, then fuel pressure couldn't be maintained. However, that type of failure would be similar to a return style fuel system FPR (Fuel Pressure Regulator) failing, which is relatively rare.
http://www.svtperformance.com/forums/engine-tuning-214/281209-frps-6.html#post7581013
Using Aaron175617's images.....
Here is what happens when things are running normal.
Pumps are pumping, fuel is being used at a reasonable rate, little bit is being dripped back into the tank through the small nipple, and the flow is going through the larger, straight shot valve.
Something has caused a pressure spike. Normally, the pumps running hard during a WOT, high RPM run and the throttle body shuts closed. ECU reacts by significantly reducing the duty cycle of the fuel injectors. Pumps keep pumping, pressure spikes through the system, and the ECU hasn't reacted. Fuel is still going through the straight shot valve and more is leaking though the small nipple due to increased pressure. Because the pumps are still creating pressure, that pressure is being applied to the side valve keeping it shut.
Computer basically goes 'oh crap!' and needs to bring fuel pressure down by cutting the pumps. As the pumps are reducing speed and pressure on the pump side of the PPRV is reduced, fuel flow doesn't pass through the straight shot valve. Instead, it pushes open the relief valve on the side and passed back through the pumps. Any pressure between the pumps and PPRV will also have some fuel come out of the small nipple.
The ECU has WAY over reacted and shut down the pumps completely in an effort to get fuel pressure under control. Cars with bad hesitation issues will actually see 0psi if they datalog. Problem is that the spring holding the side valve is designed to maintain about 67psi. Pressure will only be reduced further through the injectors. You can't really see a steady ~67psi cause the injectors are always working and reducing pressure in the system between. If the PPRV was used in a controlled environment, you'll see it holds 67psi +/-7psi.
Why they designed it that way, I have no idea. I'd like to pick the engineer's brain on that one.
I would have done something like this....
Block off the chamber between the inlet and small nipple so no fuel can pass. Open up the small nipple hole to allow a lot more fuel to pass. Set the spring pressure so that fuel pressure can be raised to 39psi (delta) plus actual boost (say 20-25psi). That means it'll blow off at roughly 59 - 64 psi. Setting it up that way might also help FRPS damages. Only down side I see is that if the side valve were to fail, then fuel pressure couldn't be maintained. However, that type of failure would be similar to a return style fuel system FPR (Fuel Pressure Regulator) failing, which is relatively rare.
ok
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I keep having worse trouble now though with delete . Keep blowing line off in tank
nice
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Unfortunately, it had been almost 3 years since I messed around with PPRVs to remember whether or not the barrel moves. From what I recall, it doesn't. There should be a matching grove in the cylinder for the barrel's ring. If you still have that cut away, could you please remove the barrel and take a pic of the cylinder? Even if that barrel moves, I can see that only affecting spring seat pressure and maybe fuel flow through the small nipple causing a reduction in flow rather than a quick drop.
The PPRV is definitely a check valve and key to quicker starts. Some people going with an aftermarket hat install aftermarket check valves to help with starts.
I believe helping over pressure while running is the misconception. There is no "blow off" feature. As designed, the relief valve on the PPRV would remain closed due to pump and spring pressure. So if the pumps were running at 100psi, the rails will see 100psi. The relief valve doesn't open until the pumps are commanded to reduce pressure and pressure in the lines is more than pump and spring pressure. I believe that it is the small hole in the nipple that helps reduce the speed of pressure spikes. When going with aftermarket pumps that flow more fuel, the hole becomes inadequate and causes excessive spikes resulting in hesitations.
However, I believe you are correct on not worrying about fuel pressure after shutting down without a PPRV. If the system doesn't hold pressure when shut off, there is no increase of fuel pressure due to heat. :beer:
Great writeup Derek but there's SO MANY 99-04 Cobras out there with pprv's still intact whether in a stock car or Modded? This debate sparks tons of opinions for and against retaining this part. The only route I'd go otherwise would be your hat setup with the Gates Immersible line,metal tubing, and reinforced clamps. I'm keeping the pprv when I put the 04 tank in next month.
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I don't think it's really a matter of debate. I believe that it is more of a personal preference. Each side has its pros and cons. As I see it:
Retaining the PPRV
Pros: easy hot starts
Cons: Significant restriction, more prone to hesitation issues
Removing the PPRV
Pros: One less restriction removed from the fuel system, elimination of shift hesitation (if caused by PPRV)
Cons: Trouble with hot starts
Personally, I chose to remove the PPRV after I saw how much of a restriction is was and because of the hesitation issues I had. Most of the hesitation was removed by the tune, but there was still a 'hiccup' in datalogs. Since I've had the PPRV removed, I have gotten use to a start up procedure that doesn't give me any issues with hot starts. So between the two, removal of the PPRV was the lesser evil.
Now, if I had my way, I'd incorporate similar functions of a PPRV into my Fore hat. That would include a check valve(s) to retain fuel pressure after engine shutdown, and a true blow off valve that can be calibrated to release pressure at a given amount just like an adjustable FPR.
The check valve is pretty easy. There are companies that already make fuel check valves that secure onto AN fittings. As for the blow off function, I seriously considered mounting a FPR near the hat so that it would bleed excessive pressure. Another idea was to drill, tap, and install some kind of check ball/spring onto the under side of the Fore hat so that excessive pressure could be bled within the tank and not need any additional exterior fittings. Only problems were experimenting with the proper spring/spring height combo to get the proper blow off pressure I was looking for. Down side is that a check valve installed outside of the hat would defeat the under hat check valve. A check valve would have to be installed between the pump and hat (not a very long hose) or before the fuel pumps (not much room between the bottom of the pumps and tank.
Considering that my only real issue is having to perform a special procedure for hard starts, I abandoned the ideas to "fix" the hat. It would be nice if a bit more time was spent in designing fuel hats so that they included check valve and proper blow off valve functions.
Retaining the PPRV
Pros: easy hot starts
Cons: Significant restriction, more prone to hesitation issues
Removing the PPRV
Pros: One less restriction removed from the fuel system, elimination of shift hesitation (if caused by PPRV)
Cons: Trouble with hot starts
Personally, I chose to remove the PPRV after I saw how much of a restriction is was and because of the hesitation issues I had. Most of the hesitation was removed by the tune, but there was still a 'hiccup' in datalogs. Since I've had the PPRV removed, I have gotten use to a start up procedure that doesn't give me any issues with hot starts. So between the two, removal of the PPRV was the lesser evil.
Now, if I had my way, I'd incorporate similar functions of a PPRV into my Fore hat. That would include a check valve(s) to retain fuel pressure after engine shutdown, and a true blow off valve that can be calibrated to release pressure at a given amount just like an adjustable FPR.
The check valve is pretty easy. There are companies that already make fuel check valves that secure onto AN fittings. As for the blow off function, I seriously considered mounting a FPR near the hat so that it would bleed excessive pressure. Another idea was to drill, tap, and install some kind of check ball/spring onto the under side of the Fore hat so that excessive pressure could be bled within the tank and not need any additional exterior fittings. Only problems were experimenting with the proper spring/spring height combo to get the proper blow off pressure I was looking for. Down side is that a check valve installed outside of the hat would defeat the under hat check valve. A check valve would have to be installed between the pump and hat (not a very long hose) or before the fuel pumps (not much room between the bottom of the pumps and tank.
Considering that my only real issue is having to perform a special procedure for hard starts, I abandoned the ideas to "fix" the hat. It would be nice if a bit more time was spent in designing fuel hats so that they included check valve and proper blow off valve functions.
A couple guys recently complained of the hesitation between shifts and they did the PPRV delete and both still have a stumble so it seems like blaming this All the time is inaccurate?
i learned one thing.. if you are powershifting and still hesitating, dont blame on the poor pprv and save yourself some time and money and get it tuned to fix the issue. I insisted that my issue wasnt pprv cuz i powershift but a couple local guys insisted that it was the pprv and i should rule it out and I did. it was NOT an easy job for me, it took quite a while and guess what? hesitation is still there.
Of course it is inaccurate. A PPRV delete isn't the answer to all hesitation issues. There are other things that could cause a hesitation. A datalog can usually spot a PPRV related hesitation. A PPRV hesitation typically shows up as a pressure spike right after a WOT run (low TPS counts), pressure spike plateaus, duty cycle drops to compensate, TPS counts go up indicating the throttle has been floored again, and fuel pressure drops like a stone. By the time the fuel pumps respond, the car noses down from lack of fuel/power.
Will a tune related hesitation be cured by a PPRV delete? Not always. A tune could be so far off that a severe fuel spike still happens and the ECU still over compensates.
Will a tune related hesitation be cured by a PPRV delete? Not always. A tune could be so far off that a severe fuel spike still happens and the ECU still over compensates.
I only had hesitation when downshifting and getting on it . If just drove straight and hard I had no issues
looks good
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