Not Enough Fuel Pump?
 

Hey guys. When I first did my vortech install the shop told me I that they upgraded to fuel pumps to a dual Walbro 340's. I never checked since I never had a problem. Now I have installed a smaller pulley, bigger 103lb injectors and e85. At only 10psi and 671rwhp with low timing, I'm losing fuel pressure past 6k rpms. It's going from about 75+ to 50psi. Looks like I'm maxing out the pumps. Will dual 400s do the trick? Aiming for 700rwhp.

When we were suspecting the fuel pumps, I took video of the gauge. As you can see, when the pull starts it starts to lose pressure. Another concern is how much the needle is shaking. Not sure if its being caused by engine vibrations or a bad/clogged fuel filter/pressure regulator. Its a 2002 so the fpr is built into the filter. Anyway to be safe I ordered a new filter since I cant even remember the last time I changed it.


LS3 with v2si.
Dynoed 671/577 at 10psi and low timing, didn't pull it all the way to 6500 due to the fuel pressure dropping.

C5 Losing Fuel Pressure - YouTube

Are your fuel lines big enough? Maybe that's why youre choking out. For E85, you need some really good flow.

Looking at HP capabilities of the 255, just one can support 600hp. Are you sure they are Walbro and not Aeromotive? Aeromotives don't flow as much in the upper psi range. Pus, I can find a Walbro 340.

I think you're right. Been looking up stuff and I think they did a twin aeromotive setup. I have a return-less system and that's holding me back a bit. I just picked up 2 walbro 400's. I guess they'll get it done for now but I'm gonna have to build a return system with a boost referenced fpr, -8an feed and -6an return lines

I found a graph comparison of the Aeromotive and Walbro fuel pumps with the same flow ratings but at different pressures. They aren't the same when pressures start rising. I should have saved it when I found it.

Thanks Damian. I really think that probably one of my pumps went out. I'll see when I pull them out on Sunday. Either way with the walbro 400's I know exactly what I got now and that they're better high pressure pumps.

Make sure that you're getting actual Walbro fuel pumps, there are a lot of knock offs out there. Quite a few SyTy guys get them, they crap out shortly after because the bought Chinese knock offs.

New Walbro 450's ready to go in


Pulled out the old setup. There were no markings or part numbers on the pumps. They look just like Aeromotive 340's and i dont know if the marking got "washed" off by fuel. I'll post pics of the pumps tomorrow.


Squeezed the two Walbros in the bucket. The bottom already had an opening so that the strainers of the fuel pumps could stick out. I had to basically just had to open up the bottom of the bucket to fit the 450's.






Needless to say, we were able to squeeze them in and everything checked out and the car runs just fine. Next step will be to get back on the dyno, keep an eye on the fuel pressure and finalize the tune. Then I can start on that fuel return setup.

Had a chance to test it out yet?

Sorry for the late response. It worked out well. The volume is there. I was able to scale back the injectors and the car was rich so I know its getting fuel now. Next step is to convert to a return style system. Seems Im maxed out on what the stock non-return fuel lines can supply.