I have a 98 z28 with a 6.0L LQ9 swap. It has a stock fuel rail, lines, and regulator with 36lb injectors currently. A little while ago it started hesitating noticeably at WOT over like 4kRPM so I tested fuel pressure and found to have 60psi at idle as it should be but then as soon as it's under load particularly 3rd gear+ at 3k+ fuel pressure rapidly drops to 20 psi at WOT. So I changed the fuel pump to a very large walbro 450lph rewired the car with 8ga to power it, and pressure is still dropping exactly the same so I know it is not a pump related issue. The car also gradually loses fuel pressure as soon as you shut it off and after about 5-10 minutes it will have 0psi at the rail. Thinking maybe a regulator issue? Could it be leaking the pressure back through the return line? And if it is a regulator issue is the a particular aftermarket one that I should buy the handle the extra load?

Thanks

 

You did try a filter first?

 

I have not tried a new filter but that wouldn't explain why it loses fuel pressure when you shut the car off? It'll idle at 55psi then drop to 0psi after 10 minutes of being off.

 

I had a similar issue in my LT1, turned out to be the fuel pressure regulator. Pressure would drop off rather quick after turning the engine off with the ignition ON.

Did you pull the vacuum line off the back of the FPR? There should be no fuel in it. Mine was leaking fuel through it like crazy.

 

I haven't dond anything with the regulator I will have to check that. Does anyone know if I need a beefier regulator for the 450lph??

Thanks

 

look at the manufacture page and see if they recomend any. if the stock one is the correct pressure for your setup and no other is recomended then go with it.