Superduty

" just replace it every three months"

What ? Are you kidding ? Are you guys verifying that these things are actually leaking at stock injection pressures ?

J.DAVY

"All the new CP3s will do is increase their VOLUME, not pressure capabilities. The best way to take advantage of these pumps is to keep the maximum rail pressure the same, ie stock and changing the TIMING AND DURATION. "

What is the maximum pressure a cp3 can achieve?

"Fuel delivery volume DOES NOT go up linearly with injection pressure. It takes 21% more pressure to get a 10% increase in fuel delivery. Much easier to just add 10% to the pulse width than to increase injection pressure."

What does 10% equate to in horsepower?If a truck was making 500h.p. @ 14000 psi rail pressure what would it make @ 24000psi?



"My advice: don't touch the rail relief valve unless it is obviously defective.[/QUOTE]"

What is the pressure they typically pop? I have heard if they pop to many times they can get scratched and not seat properly allowing some fuel to bypass.I had fuel around the banjo head fitting on top of mine.Would this have been evidence that it had popped at some point?

Superduty

"What is the maximum pressure a cp3 can achieve?"

If it is running at any sort of RPM, it will make enough pressure to cause leaks all over, in the connectors going to the injectors and in the injectors themselves. 30,000+ PSI

"Fuel delivery volume DOES NOT go up linearly with injection pressure. It takes 21% more pressure to get a 10% increase in fuel delivery. Much easier to just add 10% to the pulse width than to increase injection pressure."

What does 10% equate to in horsepower?If a truck was making 500h.p. @ 14000 psi rail pressure what would it make @ 24000psi?

500 x sqr(24,000)/sqr(14000) = 650 HP IF THERE IS ENOUGH AIR TO BURN THE EXTRA FUEL. Otherwise all it does is smoke (more).

"What is the pressure they typically pop?"

I don't have this spec. I think about 28,000 PSI.

"I have heard if they pop to many times they can get scratched and not seat properly allowing some fuel to bypass."

I doubt it. What is your source on this info ?

"I had fuel around the banjo head fitting on top of mine.Would this have been evidence that it had popped at some point?"

Nope. That is evidence that the banjo bolt is loose. The line that connects to the relief valve also connects to the back of the head and to the CP3 overflow, so there is always fuel in it and the fuel pressure should be the return line pressure, a few PSI, no more.

J.DAVY

Thanks for the info.

"I have heard if they pop to many times they can get scratched and not seat properly allowing some fuel to bypass."

"I doubt it. What is your source on this info ?"

I heard this from Keith at Diesel Dynamics about 3 years ago.I have read about it several times on the TDR since.

"I had fuel around the banjo head fitting on top of mine.Would this have been evidence that it had popped at some point?"

"Nope. That is evidence that the banjo bolt is loose. The line that connects to the relief valve also connects to the back of the head and to the CP3 overflow, so there is always fuel in it and the fuel pressure should be the return line pressure, a few PSI, no more.[/QUOTE]"

The banjo was tight so I thought it must have took a spike to make it leak.

chazecheez

go for it you only live once..

CrashCade

Is the Pressure cap the valve that comes up in the middle of the fuel rail with a Banjo bolt and a metal fuel line coming off of it? I just got a cap for mine and Want to have as much info before I start swapping it out. If that is the part it looks like it is only about a 10 minute job or so.

Is the rail under pressure without the ignition on?

Can the pressure release valve just be removed and the cap put in its place?

How do you cap off the return Line?

king d

these are good questions becuase i have to do the same thing you are going to do.without motor turning over the rail shouldnt be pressurized.i was thinking from the looks of it you just remove the old pressure valve and install the fuel cap on the rail thus leaving the old pressure valve to keep fuel from back flowing from the filter head,but i honestly have no idea and only looked at it briefly while holding my screaming 8 month old daughter

banshee

No, the rail is not pressurized when the engine is off. Yes, you can remove the valve and directly replace it with the cap. Cap the return using the two washers, a bolt and a nut.

doug60

I installed the rail cap today, I was surprised it didn't have a sealing washer between the rail & cap.
No leaks so far.

XLR8R

Why are you guys capping the return?

CrashCade

That was mainly my most important question? If it is not sealed is it going to cause air bubbles in the fuel rail system somewhere. I would think not because it is part of the return system. Is it something that it has to be done or just left zip tied out of the way?

banshee

It's hooked into the return line from the CP3 and from the injector return that comes out of the back of the head. Unless you want it to spit return fuel all over the motor you better cap it off.

XLR8R

I know, but WHY or HOW does it get opened up in the first place?

Dodge/Cummins didn't deliver it with return fuel spitting all over the engine...

There's no negative side effects to removing the pop-off valve on the common rail?

banshee

If you remove the relief valve then the banjo bolt that routes the relieved fuel will be left open since it hooks into the top of the relief valve and seals with two washers. Unless the cap you choose has a place to bolt the relief valve return line to (it will be closed, but bolted up to resemble a stock-like appearance) it will be hanging free and open. From the factory the entire return system is closed up, but if you remove this line and don't cap it somehow then the return system will be open, and that fuel will find the path of least resistance... all over the engine bay. As long as you either A) don't remove the relief valve or B) cap the return line if you do remove the relief valve then you won't have a problem with spilled fuel. As to the argument if it's hard on the rail and such... that's up to a debate. Not having any fuse whatsoever in the system is a bad idea IMO, but at this point it seems to be the only option.

XLR8R

I haven't formed an opinion yet about whether or not removing the common rail relief valve is a good idea; I'm just curious what the benefit is - to allow significantly higher rail pressures, I suppose? I don't imagine the rail itself being hurt, but the injectors might be a different story... how high are the rail pressures getting without the relief on a modded cummins?

Has anyone tried installing an orifice instead of the valve so pressure increases while retaining a measure of safety?