2017-2019 6.6L GM Duramax L5P
Lift Pumps | Injection Pumps  | Injectors

Model year 2017 marked some major changes for the Duramax fuel system. Finally, they forewent the status quo that had been hovering over this engine since 2001 with the only major change occurring in the 2011 model years with the LML engine. The fuel system featured on the L5P could best be described as a 100% complete overhaul. Without going into a complete analysis, lets give you some of the highlights at least. Number one, a fuel pump from the factory. That's right, the main cause for fuel starvation, especially on modified Duramax engines, has been addressed with the addition of a factory lift pump. And we'd say its about time, as every single other manufacturer realized this years ago. Next, you won't be seeing any Bosch insignia on your fuel system.

Again, since 2001, they've been in bed with Bosch to deliver the high pressure fuel via common rail (and later piezo) injectors and a high pressure CP3 or CP4 injection pump. Well, GM and Bosch apparently had a divorce and Denso came knocking. The Bosch CP4 found on the LML engines has been replaced by a Denso HP4 that should eliminate the countless failures of the CP4. Why? Many would attribute the failures to the roller tappet design that would self destruct at the presence of any air where the HP4 uses a much more robust solid lifter design that is also a substantially simpler design. As previously stated, Denso is also supplying the injectors with a solenoid type that replaces the Bosch piezo units found in the 2011-2016 model years. This move wasn't necessarily due to a high failure rate of the piezo injectors, more so because the solenoid type work more cohesively with the HP4 and the rest of the fuel system.

Again, these are merely the highlights of the move from Bosch to Denso with basically every other facet of the injection system changing in some degree, as well. Now, the question at hand, what's to be improved from this system? Well, time will tell as far as the true weaknesses, but for those looking to produce power levels above stock, there is definitely room for improvement. While a lift pump has indeed been integrated from the factory, its output is sub par and will need an upgrade to allow for fuel delivery to match most of the programmers on the market. The HP4 is absolutely more robust than a CP4 in terms of durability, but again, not capable of delivering sustained rail pressure for maximum power potential. How far will fuel upgrades take you and your L5P Duramax to meet your power goals?

As always, if you are having any issues determining the right parts for you and your truck, do not hesitate to give us a call at 801-571-7780 or send an e-mail to info@gillettdiesel.com and we would be happy to assist.

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