You probably removed more than just the pressure valve holder, spring and crush washer and havn't gotten the other parts back in correctly.
How many parts did you remove?
Here's the detail to refer to.
http://www.peachparts.com/shopforum/showthread.php?t=173991
Your best bet is to remove #1 frist, then #2 and copy #2 being VERY careful to note EXACTLY how everything you removed originally from #1 comes out of #2. Go no further down into #2 than you did on #1 the first time.
If that doesnt work the pump may need to be recalibrated on a Bocsh flow bench.