Would you swap a return-style (-'03) fuel system into a 'returnless' (04+) truck?

I am assisting a friend with his truck build, and have a question to run by you gents -

A tale of two trucks! The first truck is a 2003 SilveradoSS with aftermarket valvetrain and Magnusson Radix kit - this truck suffered a vehicle fire (suspect = aftermarket stereo install) and it burned badly, was a total write-off. The second truck is a 2004 Silverado SS, bone stock. The project is to swap the drivetrain from the burned SSS into the stock 2004 truck.

The issue is: the 2004 truck has the "returnless" fuel system; the donor truck has the full-return system, and is in good order. As both trucks will be completely torn apart for this thrash, I am seriously considering swapping the entire 2003 fuel system (tank, evap, lines) over to the 2004 truck, so that it will have a full return *plus* an external fuel filter. I'm pretty sure that this is technically possible and there will be no issues with chassis wiring or PCM tune etc, but I want to hear your feedback as to whether there is any benefit (small or large) to doing this swap. Would doing this swap make the truck easier to tune, or more consistent in tuning? Any other advantages/disadvantages? I am heavily leaning towards doing this swap, is there any reason I shouldn't?!

Mr. P. :)

Especially with the increased fuel requirements that the supercharger will need, that means that you will be using a bigger pump. Bigger pump equals more heat at low loads (idle, and putting around town). Because of the increased heat, making it a non-return will only compound the problem. I would go with the return system and update your flash file to compensate for it.

You and I are on the same wavelength; I gotta check the manual and see if the EVAP control wiring is the same, if so then we're reverting to the better '03 fuel system.

Mr. P.

I'm not sure of all the differences on the EVAP stuff with a return system vs. a return-less system, but if you have the hardware, then after a full flash, the only left would be if there was some other solenoid / sensor that would need to be added to the wiring harness.

Hello Mr. P,

Your ’03 SS would have originally came with an LQ9 6.0 L 4L60E 4 x 4 (AWD). As long as your ’04 truck was a V8 with a 4L60E, the wiring will be straight forward.

Some facts about the fuel delivery systems:

• ’99 - ’03 trucks used a fuel feed and fuel return line – to / from the fuel rail
• ‘04’ - 07 used a “returnless” fuel system – just a fuel feed line, no return line
• this changes the required values of B4001 (Injector Flow Rate)
• OEM fuel systems using a return line are “manifold referenced” – FPR in the fuel rail
• in these systems a 2D graph of B4001 values looks like a straight (flat) line from left to right
• in returnless systems a 2D graph of B4001 values looks like a sloped line – from lower left to upper right

I would use the ‘04 PCM and “base” V8 tune, to make communication with the IPC, EVAP system, and fuel gauge / tank - less of a pain to deal with.

Then copy over the necessary tables (B4001, etc.) to make the boosted LQ9 feel at home in the new truck.


Regards,
Taz