K-Jet testing question - Static pressure vs cold pressure?

[raueda1]

As usual, the more I learn the less I know.  After a long shake-down trip my cold pressure is low so I'm rechecking my WUR settings (I'll refer here to the CIS Diagnosis manual in the site's technical section).  I'm now confused about how Test 4, Static Pressure Test, differs from Test 7, Cold Control Pressure.

Starting at the beginning per Test 3, system pressure is tested with engine OFF, fuel pump ON and gauge CLOSED.  It's fine, 5.8 bar.  With pump off pressure drops to 2.8 bar and stays there where it should be.  This suggests that fuel accumulator, pump non-return valve and primary system pressure valve are all OK, since they're all "behind" the gauge and holding pressure.  So far so good. 

However, per the manual, this is not the proper static test, which is done with the gauge valve OPEN.  When I run the pump with valve open the pressure is only about 0.8 bar.  This is identical to my cold control pressure - it's set too low, which is what got me started in the first place.  Moreover, the cold control pressure test seems to be the same as static pressure except that cold pressure is tested with the engine RUNNING. 

This doesn't quite make sense to me.  Why would non-running engine have higher static pressure than the cold control pressure established by the WUR? As long as the gauge valve is open then wouldn't there be fuel flow through the WUR thereby reducing static pressure?  Maybe the static pressure needs to be tested at operating temperature.  Then the operating pressure would be above the the pressure that opens the injectors, so it would drop to that (~2.5 bar?) and stop?  But I don't believe this theory cause then the injectors wouldn't open before the engine was warm, a paradox.  I'm obviously missing something and don't really grasp it all.  Can anybody help?  Thanks and cheers,

[daantjie]

Dave, not sure if you have watched this vid before, nice and retro   but there are some good nuggets of info here that might spark a thought that might help you in your quest:

https://www.youtube.com/watch?v=a4fJAfXYxWk