Mine is a 3.4L and I'm running the Imagine Auto fuel head that flows more gas and is a tad more difficult to control without modifying your WUR. Here is my thread on Rennlisst:
The Factory Workshop Manual is a good place to start for determining how to test your WUR and other fuel delivery components and what the "baseline" (stock) values are. However in the end there is a certain balance that is achieved between your AFRs and WUR fuel pressures and cold/hot starting.
I followed the instructions for making my WUR adjustable (see my link above for the Pelican thread that I used) and since doing so have run "cold" WUR pressures from 2.2 BAR (rich) all the way to 3.5 BAR (lean). And using an Innovate LM-1 AFR meter, I was able to dial my AFRs to 13.3:1 at idle and 11.5:1 at WOT full boost (using the mixture control screw on the air meter housing) each time I tried a different WUR setting. HOWEVER, what I discovered was that even though I was able to achieve the same AFRs for each of these various WUR pressure settings, the car responded much differently. It obviously ran hotter with leaner WUR values and more on the cool side with richer WUR values. Too rich and the throttle response was very sluggish. And just so that we are clear by lean I mean higher pressure gauge readings and by rich I mean lower pressure gauge readings. Another rennlister named Tripster also ran into a similar scenario with his engine...at one point even though his AFRs were perfect, his header pipes would glow red hot after only a short trip. He too finally discovered the balance, I'm told and the car runs very well.
To make your WUR cold pressures drop (rich), you tap the adjustment pin in...to make the pressures increase (lean), you raise the pin.
Sorry this is so long and confusing!!!