8-9psi at idle on the stock lift pump is considered "good." However if you're dropping down to near-zero psi on a full throttle run, you may want to look into an upgraded lift pump.
Well I took it for a goo ride today, and on ocassion, I was getting 4 PSI at the CP3. I pushed the pedal about half way down. Is 4 PSI getting a little too low? Do I need a FASS?
Change ALL fuel filters before the CP3 pump then take the pressure reading at idle. This is going to be your real lift pump output pressure.
Mine is 9 psi. A drop in pressure at idle would means a clogged filter or a defective lift pump. Of course when you are not in idle, the more you have your foot down the pedal the more drop would be the pressure.
As far as the pressure is above zero psi it's fine.
I have the factory lift pump in the tank and I added an extra CAT 2 micron filter kit to my truck. I installed a fuel pressure gauge after the filters and before the CP3 and at idle I'm reading 9-10 and WOT and driving it varies between 6-13... So I'd say your pressures are ok. Mine varies quite a bit while driving..
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