Fuel Pressure Too High at Idle

[2K_Silverado]

Yes, I've searched and couldn't find a suitable thread, so here goes:

My fuel pressure is reading 72 psi at idle and I need to know how to get it down to the required 58 psi.

I've got a 430 HP LS3 crate engine with a truck intake in a 2000 Silverado. The fuel system is the factory return-style with a Walbro 255 (TU432HP-2) that pumps through the stock lines (3/8" feed, 5/16" return) to a Corvette-style filter/regulator (WIX 33737) at the engine then through an Earl's 1.5" liquid-filled pressure gauge and finally to the fuel rail.

Yesterday I replaced the filter/regulator and that didn't change the pressure reading. The engine seems to run smoothly above 1000 rpm, but at idle (700) it hunts a bit and will stall with the clutch in coming to a stop sometimes. I can keep it from stalling if I downshift until I'm almost at a stop, but it will still hunt. I can't tell what the pressure is at cruising speed since the gauge is not visible while driving, but my AEM wideband tells me everything appears to be fine. At idle, the WB displays maybe .95 - 1.05 and cruising it reads .98 - 1.02, but for all I know the pressure could still be too high. All the info I've been able to find online tells me that this fuel system setup should be good, but in my case it doesn't appear to be.

So does anyone have any ideas on how I can resolve this issue? Will this pressure cause any damage to anything, like injectors? I've read that having the pressure too high at idle can cause the idle symptoms that I'm having so I need to resolve this issue before I look anywhere else.

[mbray01]

have you checked the pressure at the rail with an actual quality hand held fuel pressure guage. I cant tell you how many times ive seen guys chasing fuel pressure problems that dont exist because a hard plumbed guage was inaccurate

[2K_Silverado]

Thanks, Michael. I thought about the accuracy of the gauge, but there's no provision on the rail to connect another gauge. That's why I added the adapter and the Earl's gauge. Since I already replaced the filter/regulator with no difference, I think the gauge is good.

If I were to add an adjustable regulator, could I block off its return port and still get a good reading? I ask because I can't find a returnless regulator that can handle the pressure and I already have the return connected to the current filter. And if I were to do that, what brand regulator would you recommend?

Thanks for your help.

[mbray01]

replacing the filter/regulator only confirms that they are good. it does not confirm the gauge is good. if a regulator is commanding 58 psi, and the gauge reads 70, then a new regulator commanding 58 psi will still read 70 psi with the same gauge. Again, not telling you this is your problem, but, the only way to verify the accuracy of the gauge is with another gauge. the 255 shouldnt be over flowing the regulator, ive seen 450's do that, but not 255's. one other thing to check is if there is a restriction on the return line, causing the pressure to spike due to fuel not being able to return properly

[2K_Silverado]

OK, fair enough. I'll see if I can find another gauge to swap in just to verify its accuracy. I'll also run a separate return line into a gas can for a quick check, however the current return line is the stock 5/16" one that's been on the truck since new. Unless some contaminant got in there during the engine swap it should be adequate. I suppose another possibility is that there's a restriction of some sort on the pump itself. That would be a hassle to get to, especially since I just filled up. D'oh!

[2K_Silverado]

I disconnected the return line from the regulator and attached a rubber hose into a gas can, you, know, just as a quick check. With that setup the fuel pressure sits at a steady 60 psi. Now I have to figure out where the restriction is...