LS Flex Fuel Injectors 12613412 12609749 12613411

1999–2003 4.8, 5.3, and 6.0L engines: fuel rail had a 3/8" feed and a 5/16" return. The fuel pressure regulator was on the rail and used a vacuum line to the intake.

2004 changes:

• Most truck engines switched to a single 3/8" feed with no return (return‑less), except 5.3L L59 Flex Fuel models, which kept the return line but used a lower‑pressure regulator.

• Exceptions: 2004 Express van and 2004 Trailblazer/Envoy kept the return‑style rail.

2005 changes:

• 5.3L L59 Flex Fuel switched to the single 3/8" return‑less rail like the others.

Fuel pressure specs:

• Non‑Flex engines: 55–62 psi (vacuum line disconnected, pump running).

• 5.3L Flex Fuel (2001–2004): 48–54 psi (vacuum line disconnected, pump running).

• 2005+ return‑less rails (all types): 55–62 psi. These return‑less rails have no vacuum reference, so pressure stays constant under all conditions.

Note: PCM programming differs for fuel flow rate based on whether the vehicle has a return or return‑less rail. This matters when having a PCM programmed.

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 & 5.3L — 21.8 lb/hr @ 58 psi
25317670, 25320288, 25323974 — 1999–2000 6.0L; 2000 4.8L & 5.3L — 24.8 lb/hr @ 58 psi
25317628 — 2001–2007 4.8L, 5.3L, 6.0L — 25.2 lb/hr @ 58 psi
25326903 — 2005–2007 5.3L L59 (flex-fuel) — 36.6 lb/hr @ 58 psi — return-less — taller than non-flex injector
12580426 — 2002–2004 5.3L L59 (flex-fuel) — 33 lb/hr @ 50 psi — return-style — taller than non-flex injector
12554271 — 1997–1998 5.7L LS1 — 29.6 lb/hr @ 58 psi
12555894 — 1999–2000 5.7L LS1 — 27.3 lb/hr @ 58 psi
12561462 — 2001–2004 5.7L LS1/LS6 — 30 lb/hr @ 58 psi
12613411 — 2010–2017 4.8L/5.3L — 36 lb/hr @ 58 psi

12613412 and 12609749 — used in 2010+ Flex Fuel engines. Drop‑in, high‑flow EV6 injectors that fit the 4.8/5.3/6.0 non‑Flex Fuel rails (same height). 50 lb/hr. Good performance and inexpensive on eBay. Uses 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

19421333 - 29lb various Gen4 trucks (alt# 12580681)

HP Tuners Format P01 P59 12613412 12609749

Injector Data

58psi base Return-Less

LS Injector Identification