Been out of the game for a while, so I’m not sure what’s the go to plan anymore for fuel system upgrades. The last turbo truck I had, I just ran a walbro 450 in the stock bucket and bigger injectors. But it was a 2010 flex truck.

current toy is a 2006 rcsb l59 flex fuel truck. I’ve already done suspension, transmission and rear end upgrades. So now it’s time to make some power! Currently, the 5.3 just has a healthy cam, headers, tbss intake and supporting mods. I’m planning to pull the headers and exhaust off, slap a trick turbo hot side/manifold setup on it and a vsr billet 78/75 turbo with Intercooler. I plan to run 8-10psi of boost. If it makes 600-650 crank hp, I’ll be tickled shitless. it will be ram on 91 no ethanol fuel primarily, but I do have a content sensor plumbed in already and fill up with e85 occasionally when I’m in a town that has e85. Obviously, with the turbo, I’ll be more inclined to run e85 every chance I get.

So obviously I know I need to do some fuel system upgrades. I pondered converting it to return style for boost referenced fuel pressure, as I have a nice aeromotive fpr laying on my tool box. But I’m wondering if I’m creating more work for myself than necessary. Could I run a walbro 450 in the stock bucket (modified of course) with a Hotwire setup, throw some 80#/850cc injectors in it and call it a day?

 

The 450 will overpower the stock in tank FPR. Your idle fuel pressure will be HIGH.

 

Well, I know that’s the obvious first thought. I just wondered if you could enlarge the Venturi hole or any other modifications to the bucket itself to make it happy. Haven’t kept up with fuel mods in a few years. Only reason it worked on my 2010 I believe is because it was a pwm pump control and used the pressure sensor to dictate pump output.

I have successfully used 340lph pumps in stock buckets in the past. But I don’t think that would be enough for 650hp on e85

 

Enlarging the Venturi hole only helps post fuel pressure regulator. If you build a return set up and utilize the Venturi with it then you have to enlarge the hole if you’re running a bigger pump. If you’re running the stock in tank regulator then that is your limiting factor

 

Gotcha! Well I had planned to use the fpr I have and run a new feed/use stock line as return. Just wanted to make sure I wasn’t doing more work than necessary

 

You can do that

 

I got a trick turbo kit with the same turbo you want in my 07 classic. I run the drop in 72# injectors and a walbro 450. Truck made almost 500whp on 8.5#. Tuner said I was at like 65% duty cycle. It'll be fine.

With that said. I have a Holley FPR and rails and I'm getting ready to run either a dual 340 or 450 setup and go return style to convert to e85 and up the boost.

It may also help me that I bought a new fuel sending unit off rock Auto and it doesn't send the fuel thru that venturi thing at the bottom of the bucket. It just dumps the fuel right in to the bucket via a hose. From what I read of you drill out the venturi it helps. The flow and keeps the FPR from getting backed up. Either way my truck runs awesome and I have no issues.

 

I just put a Walbro 450 in my stock 2011 Sierra Denali L9H Flex Fuel bucket assembly. After all kinds of issues trying to put the 450 in the stock fuel bucket and cutting, modifying, and trying to attach hoses and things, I just gave up and it just kind of sits in the bucket but doesn't move.

Unfortunately it looks like I have exactly the same amount of flow with this 450 as I did with my stock Bosch 04421 pump. I run E85 basically 100% of the time, but I really think if I could get the FPCM to do what I want and command 100% duty cycle at higher fuel flow, then I think it would hold pressure at WOT. The FPCM will only allow it to go up to about 88% duty cycle, sometimes I saw it go to about 92% when I had the stock pump in there. It dosen't make any sense, since the demanded fuel pressure is almost 25 psi above the actual but it still refuses to go any higher on the duty cycle. I actually don't think its a hard maximum duty cycle limit either since it will get to the around 88% maximum and go up and down a few .1's of a percent, but not just hit an exact % and not go any higher.

I think we are missing the tables we need in HP Tuners to properly control the GMT-900 FPCM (FSCM). I am trying to think of ways I can just bypass it, like by unplugging the fuel pressure sensor and maybe forcing it to use the open loop tables, and then setting the open loop tables to 100%. I just haven't tried that since if I unplug the fuel pressure sensor then I won't know what the actual fuel pressure is.

And I agree 100% with trying to keep the returnless system. I think its way better than having to deal with a huge regulator and pluming new non-stock lines and creating a whole bunch of other mess when I think we can make do with what we have. I know people probably love to get rid of the returnless because they want to get rid of all "emissions" stuff. I think its a lot better being able to directly control with software different pressures for boost and all that, we just need HP Tuners to support what they claim to support and get things working right.

I do understand though once you hit a certain point, it may be a lot easier to just rip everything out and go return system, but I have been wondering how the stock FPCM would do if you tried to run dual pumps off of it and if there is enough room with the control and trims to back down the duty cycle at idle to run dual pumps.

 

I’m interested in the outcome. I am planning something similar. Right now I have a stock Delphi fuel pump with kb bap on a 2005 GMC Yukon Denali.

 

Not sure if you were talking to me, I think you have a returnless system too? I think they switched around 04 or 05 but maybe not on everything. I am also not sure how they were controlled, if they had some segment of the ECM controlling them or if they had soem logic in the ECM but a dumb type of driver on the pump sender/hat assembly thing?

But I think I might try putting in a 525 Walbro since they aren't that expensive, and I don't seem to have any more options. We won't get any support for FPCM tuning, and since I want to keep my stock style returnless and stock style lines, I can't convert to a returnless. My other option I guess would be to try to add an extra pump and find some type of triggering control on it, but not sure how I would fabricate a holder for it and how I would integrate the line from the extra pump to the main fuel line. I haven't seen any details on how people do that. I know some people go as simple as a switched based on boost to run straight battery voltage to a secondary pump but I just don't know how they are connecting the fuel line from the additional pump or if they are just tee'ing it to the orginal fuel line maybe with a check valve in line or something like that.