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GMT900 Fuel Setup For Big Power

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Old 01-05-2017, 09:44 PM   #1
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Default GMT900 Fuel Setup For Big Power

Ok figured I would post up my take on building a good high hp return style fuel setup for the GMT900 trucks with the FPCM.

My setup is easy, straight forward and can be done with several different pumps, regulators, exc... I happened to use a Maganfuel 4303 fuel pump with a Magnafuel boost referenced regulator.

First off starting from the back of the truck going forward. Lets get power to the fuel pump. In the very rear of these trucks mounted on the drivers side above the spare tire you have a FPCM (Fuel Pressure Control Module) that powers and controls your factory return less fuel pump. If you pull the connector off and remove the cover for the pins you will see the pin numbers and wires going into the connector. The wires we need are the main ground coming in (Black wire 10AWG) main power ( Pink/white stripe 10AWG) and pins 47 and 16 directly opposite of the power and ground. These pins, 16 being pink (Pump ground) and 47 being grey (Pump power). Also Pin 13 will be used (dark green/white stripe) for relay trigger.

Whole point of de-pinning the FPCM connector is to re-pin to a weather proof fuel pump relay.

What I did was ordered up a Painless weather proof fuel pump relay from Jegs part# 764-30131 and connected the black ground from the FPCM harness to the pink 12AWG pump ground and pin 85 on the relay. Pin 30 on the relay goes to the 10 AWG pink power wire from the FPCM, pin 87 on the relay to the grey 12AWG fuel pump power wire, and the green trigger wire to pin 86 on the relay. Now I chose to just use the factory 12AWG fuel pump power wires. They seem to work just fine for me and the pump doesnt pull more then 14 amps so I think I will be fine. You can run your own fuel pump wires if you want, doesnt change anything, I did it my way since everything was there and ran by the factory so didn't see the need to cut the harness open and run new pump wires. The main power and ground wires that feed the FPCM are 10AWG and should be plenty to feed a big single or dual pumps.

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Ok so now we have the power we need to feed an aftermarket fuel pump, you can reconnect your FPCM connector just so its not hanging under your truck. As for the relay I just mounted it next to the FPCM and taped up everything. With the harness retaped and cleaned up, other then having a relay now still looks and even still functions like factory. You will not loose your remote start function, everything will still work like factory.

In the tune all thats needed is to turn off a couple "loss of communications to fuel pump" codes which I believe are P0230 and U0109. With those codes off you won't throw a check engine light and everything will be happy.

OK so power side done lets move to the fuel pump...

My truck runs a healthy 427 LSX with twin turbos so I needed a big pump. I went with the Magnafuel 4303. Should support about 1100 on e85. Ill be adding a second one later but for a majority on here its plenty. Now like I said before you can run any pump you like I'm just giving an example of what I used.

My truck started off as a flex fuel truck but all works the same weather yours is a FF truck or not. So pretty self explanatory pull the pump out of the tank and remove all there internals...

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Removing the internals is very easy, just push in the tabs and pull the entire center part out. This will give you a nice open bucket to work with...

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Little shot of the old stock FF pump that has had a great run and supported quite a bit of power vs the new fuel pump that will handle a lot more HP...

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To make this pump fit I used a stainless "sock" filter from Fuel Lab part# 83801 and connected it to the inlet of the fuel pump. Made a window in the bucket to fit the sock through and also to keep the bucket full even under WOT conditions. So far so good, fuel pressure stays solid. Was kinda worried I would suck the bucket dry but fuel pressure has been solid with no signs of fuel starvation. Time will tell when I really turn it up. The stock feed which is now the return feeds the bucket so hopefully it keeps it full.

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Now that the pump fits I drilled a hole on the lid of the bucket and ran a -8AN bulk head fitting from Russel. After that I removed the springs on the bucket because I had to run a hard line on the pump outlet to the bulk head fitting. Reason be the 4303 fuel pump is so tall, normal hose end fittings wouldn't be short enough and just wouldn't have room. No issue for me since I used some 1/2 (-8) stainless tubing with some B nuts and sleeves and flared the ends to match the 37* flare of the AN fittings...

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Alright, you got power and the fuel pump of choice in the bucket. Now to finish off the rest of the system. Basically this is the easiest part, I ran a -8 hose to a fuel pump post filter then to the back of my Holley fuel rails and mounted the fuel pressure regulator to the front and connected the return from the regulator to the factory feed line. Since the stock internals of the fuel pump bucket are removed there is no restriction in that line and works perfect as a return. I ran a -6 AN line from my regulator to the factory feed line since the factory uses 3/8(-6AN) tubing. You can find the adaptor to convert the factory tube fitting to an AN fitting from JEGS, Summit and even Nitrous companies sell these fittings. Run a hose from the regulator to that fitting and done.

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Before I forget the factory feed line has a fuel pressure sensor that uses a female 1/8th NPT thread, I tapped and ran a double male 1/8th npt fitting on my fuel pump post filter and now I can monitor and data log fuel pressure on HP Tuners like factory. Obviously once removed don't forget to cap the fitting on the stock feed line.

Thats it! Very straight forward, hopefully this helps the guys who are thinking about adding more power to their trucks and helps clear up any questions about this swap. Ill be refining this post to be easier to understand and update it as time goes on with any new findings.

Last edited by Three6GMC; 01-05-2017 at 09:52 PM.
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Old 01-06-2017, 08:28 AM   #2
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Awesome write up. Thanks for sharing.
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Old 01-06-2017, 09:08 AM   #3
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Great job on the write up. Surprised you didn't use -10 hose for the fuel pump. Do you plan on adding another in the bucket or somewhere else?
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Old 01-06-2017, 10:33 AM   #4
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Quote:
Originally Posted by Atomic View Post
Great job on the write up. Surprised you didn't use -10 hose for the fuel pump. Do you plan on adding another in the bucket or somewhere else?
I thought about using -10 but the outlet of the pump is only a -8 and the rails are -8 so figured no point in upping 6ft of hose just to neck back down. A second pump will be installed with a diesel sump on the stock tank. I'll post more info on that when I get it all in.
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Old 01-07-2017, 09:50 AM   #5
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Great write-up man! I just may have to file this away for my future FF upgrade needs. I particularly like your supply power upgrade and may "borrow" that method for my current setup as Atomic already warned me against using my factory wiring on my walbro 450. The only saving grace may be that I'm still using FPCM with the PWM fully enabled so its not demanding the high current for very long periods of time...not sure but we'll see.

Thanks!
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Old 08-15-2017, 12:34 PM   #6
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Default Oem flex fuel sensor.

I have a 2011 gmc sierra 5.3 that's factory flex fuel and returnless. I'm wanting to convert it to RETURN style and dual walbro 450 intank pumps as I'm looking to run pump e85 once I turbo my truck. How do I run my new feed line so my flex fuel sensor can still monitor my ethanol % and can i run both pumps off the power supply for the fpcm as you mentioned above?
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Old 08-25-2017, 07:15 PM   #7
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How much power are making or going to make? That is a very nice set up you have created. Best of luck!
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Old 09-23-2017, 01:36 AM   #8
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Quote:
Originally Posted by NuB4life View Post
I have a 2011 gmc sierra 5.3 that's factory flex fuel and returnless. I'm wanting to convert it to RETURN style and dual walbro 450 intank pumps as I'm looking to run pump e85 once I turbo my truck. How do I run my new feed line so my flex fuel sensor can still monitor my ethanol % and can i run both pumps off the power supply for the fpcm as you mentioned above?
need the same info
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