I have a walbro high flow fuel pump(255)...Why is it that when I install my stock FPR, fuel pressure is high(like around 45psi)..Stock psi is around 34 psi, so why doesnt the Stock FPR read 34 insted of 45-50 psi?

 

If your using a walbro intank fuel pump, its advised to switch your stock FPR, over to adjustable fuel pressure regulator to turn down base fuel pressure. Its normal that your seeing 45-50 psi at baseline

-matt

 

The answer to your question is that you are overpowering the stock FPR it cannot handle the high flow. It was designed to handle approx 1/2 that amount so it can't discharge all the extra to the return so pressure builds up. Like Matty said you will need an aftermarket FPR to regulate the pressure.

 

what if u did the 3.5 swap on ur 98 lets say and u used a stock 98 fpr and through in a walbro you dont need to turn it down do you?

 

Not sure if anyone has tried to see exactly what the pressure is on a 3.5 swap with a 255 where the pressure required is 51, but if it did it would be pure luck. Just have to pass it off as one of the necessary requirements when you put in a pump. No stock FPR is going to handle a Walbro 255 and keep the stock fuel pressure on a 4th Gen. If you put in a hi-flow pump you also need an aftermarket FPR.

I'm putting a 190 in my 3.5 swap and still going to use an aftermarket FPR.

 

Can the stock 4th gen fuel pump handle a fully modded 3.5? From what I remember neither the injectors or pump needed to be upgraded until 300 whp or so. Correct?

I know we need an aftermarket FPR, though.

 

Don't think we are going to run out of fuel with a stock 4th gen pump in a 3.5, although the extra pressure will tax it a bit more than stock.

I think a 190 is good for over 500 HP so the stock one should handle a bunch all right. For FI you have to have a pump but certainly running N/A wouldn't really need it. The only reason I am running the 190 is that my old stock one failed and I just replaced it.

 

Ok perfect. One less thing to worry about.