LS Flex Fuel Injectors 12613412 12609749 12613411

1999-2003 4.8, 5.3, 6.0 all had a fuel rail with 3/8" supply line and a 5/16" return line. The fuel pressure regulator is on the fuel rail and has a vacuum line to the intake manifold. In 2004, truck engines went to a single 3/8" supply line, with NO RETURN LINE (return less) except 5.3L L59 Flex Fuel vehicles. For 2004, Flex fuel engines KEPT the return line, BUT used a fuel pressure regulator with a lower pressure rating. 2005 5.3L L59 Flex Fuel engines switched to a single 3/8" supply with NO RETURN line in 2005. Non flex fuel engines, fuel pressure spec is 55 to 62 psi with vacuum line disconnected, fuel pump running. 5.3L Flex Fuel engine 2001-2004, 48-54 psi with vacuum line disconnected, fuel pump running. 2005+ with return less fuel rail all shared same fuel pressure spec, 55-62 psi. There is no vacuum reference on these, so fuel pressure should remain constant under all operating conditions. The computer is programmed differently for fuel flow rate depending on type of fuel rail. This is important to know when having a PCM programmed. (Exception: 04 express van and 04 trailblazer/envoy still used return style fuel rail, 05+ single line, return less rail)

Fuel injector flow rate is very important to have programmed correctly in your PCM. Find a small 8-digit number located on side of each fuel injector. Here is the breakdown.

25317669, 25320287 - 1999, 4.8L and 5.3L - 21.8 lb./hr. @ 58 psi

25317670, 25320288, 25323974 - 1999-2000 6.0L, 2000 4.8L and 5.3L - 24.8lb/hr. @ 58 psi

25317628 2001-2007 - 4.8L, 5.3L, 6.0L - 25.2lb/hr. @ 58 psi

25326903 - 5.3L L59 Vin Z, flex fuel 5.3L - 36.6 lb./hr. @ 58 psi, Return-Less (05-07) These are taller than the non-flex fuel injector

12580426 - 5.3L L59 Vin Z, flex fuel 5.3L - 33 lb./hr. @ 50 psi, Return Style (02-04) These are taller than the non-flex fuel injector

12554271 - 1997-1998 5.7L LS1 - 29.6lb/hr. @ 58 psi

12555894 - 1999-2000 5.7L LS1 - 27.3lb/hr. @ 58 psi

12561462 - 2001-2004 5.7L LS1, LS6 - 30lb/hr. @ 58 psi

12613411 - 2010-2017 4.8/5.3 - 36 lb./hr. @ 58 psi

12613412, 12609749 - used in 2010+ Flex Fuel engines, these are drop in high flow injectors, that fit the rails on the 4.8/5.3/6.0 non flex fuel engines. (Same injector height). These are 50lb/hr. injectors. Good performance injector, and CHEAP on eBay. These do use the EV6 connector, like the L59 injector.

HP Tuners Format P01 P59 12613411

Injector Data

58psi base Return Style

HP Tuners Format P01 P59 12613411

Injector Data

58psi base Return-Less

HP Tuners Format P01 P59 12613412 12609749

Injector Data

58psi base Return-Style

Siemens Deka 80lbs Injector Data

HP Tuners and EFI Live Format

HP Tuners Format P01 P59 12613412 12609749

Injector Data

58psi base Return-Less

LS Injector Identification

GM used various different sized fuel injectors across engine sizes and vehicle platforms. I have compiled this data from looking at many different calibrations. GM also changed the style of fuel rail from a type with vacuum referenced regulator, supply and return lines, to a return-less system without a regulator in 2004 for all Pickups, SUV's and so on. The ONLY exception is Flex Fuel 5.3L (L59 Vin Z) kept the return style rail for model year 2004, and in 2005 went return-less.