First: which is higher pressure... tightening the screw in turn looseining the spring? or loosening the screw in turn tightening the spring? I'm thinking loosen the screw which forces the cup up tightining the spring makes more pressure, am I correct?

Second: will the pressure effect the way the car runs as a whole includeing idle?

I drilled out the cap and put the pressure where I had thought it was originally so I could tune from there, was that original position with the tab 3/4 up or 3/4 down? (when you are looking at it on the car)

 

making the spring tighter is raising the fuel pressure as far as i know. thats how i have done it on mine

 

I would like to know the result of higher pressure and idle charachteristics also. Anyone?

 

i havent ever seen any difference in idle.and i mess with mine all the time just to see if it gets any better

 

An adjustable AFPR doesn't do too much for idle & part throttle performance unless the fuel pressure was too low to start with. In that case you may see the throttle response & part throttle performance you should have from the beginning.

There is certainly a minimum pressure required for the engine to idle & run properly. However, the ECM very accurately controls how much fuel enters the engine in order to maintain the proper air/fuel (A/F) ratio, except at wide open throttle (WOT). It does this by controlling how long the injectors are open. At WOT the ECM basically runs the injectors full open and the injector size & fuel pressure control how much fuel is allowed to enter the engine. So, having an adjustable fuel pressure regulator allows you to adjust the A/F ratio at WOT.

There's a tech article on this site to determe if your A/F ratio is correct. You can also make up a serial cable for a laptop PC and use software like WinALDL to determine this.

 

Two things. First, your description of WOT fueling is incorrect. The ECM has just as much control over PE (power enrichment, aka "WOT") fueling as it does part throttle. The only difference is, you lose the closed loop control via the O2 during PE. But via EPROM burning, you can dial in any amount of PE fuel you desire, so long as you are operating under 100% duty cycle.

Second, there is no way to determine A/F ratio by talking to the ECM through the ALDL port. That's not to say it's useless to do, on the contrary. There are a LOT of useful outputs, it's just that reading the O2 sensor to determine PE AFR is only going to tell you that you're running richer than 14.7:1. How much richer is completely up in the air (O2 voltage varies not only by AFR but also EGT).