I just recently switched from the stock FPR to the AEM and put the Walbro 255lph fuel pump in. I set my idle fuel pressure on the AEM FPR to exactly what the stock was, 47 psi(I checked it before putting the AEM FPR on). But now in boost I am running high 9 to low 10:1 A/F when I was 11.5:1 with the stock FPR. I had to adjust the AEM FPR down to 30 psi at idle to get the A/F back to 11.5:1 in boost and the way it used to be with the stock FPR.
Does anyone know if the stock FPR is 1:1 like the AEM? Meaning that it raises 1 psi of fuel for every psi of boost.
Could my fuel return orifice of .100" be too small for the flow of the 255lph fuel pump? Should I change to the .150" orifice and see what happens?
Also, I want to mention that when the AEM FPR was set at 47 psi at idle, I would come off of throttle and the idle rpm would drop way low for a few seconds and become rough and then stabilize back to normal.
What have most of you guys who are running my basic setup done to get their AEM FPR working correctly?

 

Did you disconect the vacuum from the AEM FPR when setting it?

 

No, but I also didn't disconnect it from the stock FPR when checking it at idle either.

 

You need to disconnect it when setting the fuel pressure.

 

So then; set it to 47 psi with the vacuum line off?

 

yes.


I made your mistake too and the car was runnig very rich, when I took of the vaccum line I was above 55 psi!! at ilde

 

I'll try it tonight. Thanks Juan and Sideways.