I just installed a Walbro 400 and hot wire kit into my 01 5.3L with otherwise stock return fuel system, 72# (@ 4bar) injectors. My fuel pressure at idle is now around 67psi with the vacuum line attached. Does this mean I'm overpowering the stock fuel pressure regulator? I was told this would not be an issue.

Until I can get it fixed, will there be any downside to driving it like this? I will adjust my injector flow rate table to account for the higher pressure. And I will not go WOT because I suspect the fuel pressure will actually drop as the engine uses more fuel and the FPR is able to reduce the pressure.

 

Did you check it before the swap? Mine was right around 70psi with 255 pump.

 

Yes, before with the 255 it would idle around 54psi with the vac line attached, and around 58psi with the vac line removed.

 

pump is probably getting more volts

 

This is all true, but the fuel pressure regulator should maintain 58psi (varying with engine vacuum) no matter the pump volts or volume flowing through the regulator. But it would appear that the Walbro 400 is exceeding the flow capability of the stock regulator causing a higher fuel pressure. Also when the vacuum line disconnected the fuel pressure does not change, another indication that it is being overpowered.

So what are the options here? Leave it be and adjust the tune? Fuel pressure may be more unpredictable as flow rate and engine vacuum vary.
Aftermarket FPR?
Port the regulator? Anyone done this?
Bypass/gut the regulator? This would remove the ability of the regulator to increase pressure in boost.

 

If you can't modulate fuel pressure with vacuum, you have a problem. I'd try a hand pump and see if you can or can't.

If you can't, you may need to pull the tank again & look very closely at the assembly of your bucket. I think yours is the style that has the return fuel going into one of the "legs" that attach the upper & lower sections of the bucket. There's a good chance that it's put together wrong, and as a result not flowing enough fuel back into the tank/bucket. I have seen this first hand on a Walbro 255, and an A340.

Hope that helps.

 

The regulator was able to regulate pressure with engine vacuum just fine before swapping the pump. Yes, that is the kind of bucket/return I have. There is no wrong way to assemble it, only goes together one way. There is no way to obstruct the return line in the module.

 

I assure you that your problem is in the tank. I have had this problem 2 times, and both were corrected after taking it all apart again & rechecking my installation.

 

Can you elaborate on the issues that you had? Or did you just take it apart and reassemble it and it was fine?

I could take the return line off the module and if the fuel pressure drops then that would mean the issue/restriction is in the bucket somewhere. Correct?

 

So I made a bypass plug to replace the stock fuel pressure regulator and the idle pressure went from around 65psi to 38psi, so the stock FPR was a major restriction. I suspect there are other restrictions in the return line, bucket, or rails that are preventing it from going below 38psi, but I'm not too worried about it. I can now use an aftermarket regulator to dial in the pressure I want, as long as I'm not attempting to get less than 38psi.