I understand, but I've been here long enough that most people here realize that I don't go spewing off what I "think" unless they are asking for an opinion. I posted the procedures in the manual which was confirmed by JStieger. If you don't want to believe it, I can't do any more than that. To lay this to rest, lets just say that my procedures are for testing the valve in an 03 as stated in the 03 manual. Since your dealing with an 05, we will assume it may be different and anyone with an 05 that wants to test it should do their own research or pay the dealer. Lay it to rest with that.

 

"There are two very important things you are not taking in to account.

1) Pressure in the rail is regulated by the fuel return valve (or pressure control valve as Bosch calls it) in the CP3. If the rail needs more pressure, the valve closes a little and pressure goes up. If the rail has too much pressure, the valve opens a little more and pressure goes down. Simple. The fuel return valve in the CP3 gets all instruction on what to do from the ECM and is always connected to the ECM (via those two little wires you see going to it). If the ECM looses its signal from the rail pressure sensor, it will not allow the return valve to shut, forcing rail pressure into the stratosphere. For lack of a better term, we will call it fault protection."


I totally agree, except that you forgot something: the ECM needs the rail pressure sensor to know how much juice to give the FCA. The FCA itself knows nothing. It has no sensors. It is only an actuator. The rail pressure sensor makes the CP3/Rail/FCA/ECM/Rail pressure sensor a closed loop system. As soon as you unplug the rail pressure sensor the loop is open and the ECM drives the FCA hard trying to get a decent pressure feedback signal.

It is unclear to me what happens when the ECM loses the rail pressure signal. According to your first post, the rail pressure skyrockets. The ECM has fault codes for a missing rail pressure sensor signal, but it also has fault codes for being unable to control the rail pressure, so obviously both can happen.

"2) The CP3 runs off engine speed. The amount of fuel the CP3 is capable of producing directly correlates to the speed at which the engine is turning it. This test is done at idle speed."

Yeah... it is a constant volume pump except for the inlet metering, but lets leave that aside.

"So, couple "fault protection" (return valve open) with the fact that the CP3 is not capable of pumping enough fuel at idle to run a lawnmower, together with the fact that what is in the rail is constantly being bled out via the injection cycles, and you have yourself a scenario where the rail pressure will not be no where near what you are thinking."

Wrong. The CP3 is capable of full PRESSURE output even when it is turning slowly, ie at idle, and producing a low flow rate. Even at idle it produces way, way more fuel than the injectors require if commanded to. If the FCA is mis commanded the CP3 is more than able to spike the rail pressure at idle.

"Unfortunately, I have never measured it during that scenario, so I just don't know what that pressure is."

I've never measured them on an engine, but I've seen them run on test stands.

"All I can do is speculate that given the failsafe nature of the system, the engineers that gave this to us would never let it self destruct any part of itself under any scenario as long as it was still in control (i.e. without a pressure box fooling it)."

Wrong again. If the system was truly failsafe, then why would they ever need a rail relief valve ? Do you think Cummins bolts a $400 valve on an engine for the fun of it ?

"Sealing 26,000 psi is easy to do with metal on metal if that is what needs to be done. With the injectors, that needs to be done and pressure is not working against the needle coming in from the side. The solenoid provides the force to open it when it is time. The relief valve is purely mechanical and pressure is always pushing against the plunger in the direction it moves, trying to make it open. Big difference there bud."

The injectors use a pilot valve. In all valves the pressure works against the closing element.

"Now, realizing that we are way off topic and I'm spewing all this out and the 05's may be a different"

They aren't. They are almost identical in operation. A few parts may have been redesigned.

 

what did I start here

 

Here is the tool:
Page 60 in the service manual. The threaded part screws into the top of the relief valve and you attach your hose to the other end. The part number is the number listed below the picture. Still looking for the manufacturer, but not having good luck.

 

Something else to consider.....the relief valve is basically a safety "pop off" valve in case the rail psi gets too high. It is not designed to do this operation to many times. Excessive rail psi that causes the valve to open can actually cut the seat in the valve rendering it useless as it won't seal any longer.

 

Here's some pics of the test procedure in question from my manual that I bought from Tech Authority:

http://www.turbodieselregister.com/u...p?userid=15605

Here's the Tech Authority link - use Category = Training manuals and Sub Category = Fuel Systems:

https://techauthority.gltghosting.co...atalogId=10051

 

"It is not designed to do this operation to many times."

Where did you get this from ?

 

Where did I get this from??? the school of hard knocks. On the 03's sometimes it was difficult to isolate a "bad" injector. Tech would have us unhook the fuel control actuator which would drive the rail psi to the moon and would often show the suspicious componant on the power balance test, however, you had to be quick because if you took too long or repeated the test too many times damage to the valve could/would occur. It was explained to me that this "safety valve" was in place to protect the lines and injectors from excessive psi and that if there was enough psi to unseat the valve the impending fuel flow actually cuts the seat of the valve which in turn will cause a psi leak which will cause drivability issues and possibly no start conditions. I experienced one that turned into a "no start".