Fluctuating fuel pressure

[Fla Eagle]

I have a 2007 5.3 non flex fuel and checked my fuel pressure out of curiosity since I have 170k miles and got a reading of 42 psi. So I went ahead and replaced fuel pump. Replaced and checked pressure, went up to 70 psi when turned on then slowly dropped to 45 psi. If I leave it for 30 min it drops to 20 psi. While running it starts at 70 and drops to 45 and holds steady but about every minute it shoots up to 65 psi then drops back down. It's my understanding I don't have a fuel pump regulator so I'm at a loss. Truck starts and runs great. I was getting some spark knock under mid to heavy throttle on several different tanks of 89 with the stock tune is the reason I checked fuel pressure. Abby ideas?

[rjgti]

fuel pressure regulator

[Fla Eagle]

I thought these trucks did not come with a fuel pressure regulator since it is return less system or whatever they call it?

[rjgti]

sorry missed the year of your truck

[DanDaMan956]

PLEASE TELL ME YOU FOUND A SOLUTION TO YOUR PROBLEM!!!! I AM HAVING THE SAME THING WITH MINE!!! SAME YEAR AND EVERYTHING!!!

[silveradosid]

there is still a regulator it is built into the pump assembly

[Supreme Pizza]

On 5/31/2015 at 12:05 PM, Fla Eagle said:

checked my fuel pressure out of curiosity since I have 170k miles and got a reading of 42 psi. So I went ahead and replaced fuel pump

 

   Maybe carbon on the pistons is causing the knock. It gets red hot and causes pre-ignition. Try a SeaFoam piston steam clean.