If you’re tired of worrying about the factory CP4 on your 2011–2016 LML Duramax, converting to a Bosch CP3 is one of the best reliability upgrades you can make. The Fleece Performance LML CP3 Conversion Kit W/O Pump (FPE-LML-CP3-NP) gives you the hardware you need and lets you choose the exact CP3 and regulator combination that fits your build and budget.
Below is a practical guide you can use to decide which pump (LB7, LLY, LBZ, LMM) and which regulator (LBZ/LMM) to run, what most people are using in the real world, and when it makes sense to step up to the complete kit with pump.
Fleece offers two main options for converting your LML from a CP4 to a CP3:
FPE-LML-CP3-NP – LML CP3 Conversion Kit W/O Pump
Hardware-only kit designed to install a Bosch CP3 on 2011–2016 LML Duramax trucks originally equipped with a CP4.
Includes CP3 mounting adapter, high-pressure fuel line, feed and return lines, fittings, and required hardware to bolt in a CP3.
Requires a suitable CP3 pump and tuning that supports the conversion.
FPE-LML-CP3-WP – LML CP3 Conversion Kit WITH CP3K Pump
Complete kit that includes the same conversion hardware plus a new Bosch-based CP3K pump.
Engineered as a drop-in, emissions-compliant solution with no extra parts hunting; marketed as a “no tuning required” CARB-compliant setup when used as directed.
For customers who want the simplest, one-box solution, the complete kit with pump (FPE-LML-CP3-WP) is usually the best choice. For those who already own a CP3 or want a specific Bosch pump, the FPE-LML-CP3-NP hardware kit gives you the flexibility to build your own combination.
The no-pump kit is designed around the Duramax CP3 family, so you can use CP3s from LB7, LLY, LBZ, and LMM trucks with the proper setup.
Here’s a clear breakdown for readers:
Used on early 6.6L LB7 Duramax trucks.
Bosch family: 0 445 020 005 style CP3 (often cross-referenced under common GM and Bosch reman numbers).
Works with the Fleece FPE-LML-CP3-NP kit when:
You install an LBZ/LMM-style regulator (FCA) in the LB7 pump body.
The truck is tuned appropriately for an LBZ/LMM-style CP3 conversion.
This makes LB7 pumps a good budget or core-reuse option when you update them with the correct regulator.
Used on 2004.5–2005 LLY Duramax trucks.
Very similar housing and internal design to LB7 CP3s.
Same rule as LB7:
Install an LBZ/LMM FCA in the LLY CP3 housing.
Run it with an LML CP3 conversion tune built around LBZ/LMM regulator behavior.
As with LB7, this is a good way to repurpose a clean LLY pump if you already have one.
Used on 2006–2007 LBZ Duramax trucks.
Bosch family: 0 445 020 105 CP3, the common “LBZ/LMM” pump.
This is the preferred pump style for most LML CP3 conversions and the style Fleece and other manufacturers design around.
An OEM-style LBZ CP3 with an LBZ regulator is basically the standard for LML conversions using the FPE-LML-CP3-NP kit.
Used on 2007.5–2010 LMM Duramax trucks.
Functionally the same CP3 family as LBZ, including the regulator style and control strategy.
Also considered an ideal match for LML CP3 conversion kits.
In practice, when you see “LBZ/LMM CP3,” it’s the same thing for conversion purposes.
On an LML CP3 conversion, the choice of regulator is just as important as the pump casting.
The industry standard for LML conversions is an LBZ/LMM-style fuel pressure regulator (FCA).
Fleece and other kit manufacturers base their “no tuning required” and “conversion-safe” calibrations around this later regulator’s flow vs current behavior.
This is the regulator you want to feature and link to from your blog as the recommended choice.
LB7 and LLY CP3 housings accept LBZ/LMM regulators without custom machining; the mounting and sealing are compatible.
Once you install an LBZ/LMM FCA, the ECM and tuning can treat that pump as an LBZ/LMM-style CP3, which is exactly what LML CP3 conversion files expect.
This lets customers reuse existing LB7/LLY pumps while upgrading to a more modern regulator and control profile.
The original LB7/LLY regulator was designed for earlier rail pressure targets and control strategies.
LML tunes and modern conversion calibrations assume the LBZ/LMM regulator curve, especially at higher commanded pressures.
Running an early regulator with tuning that expects an LBZ/LMM FCA can cause:
Rail pressure tracking issues.
Idle surge or hunting.
Fuel pressure codes under load.
Swapping to an LBZ/LMM regulator is a simple, proven fix—and a good upsell opportunity to your Bosch regulator listings.
For most LML owners, the differences that matter are practical:
Physical fitment
All Duramax CP3 pumps (LB7, LLY, LBZ, LMM) share the same basic footprint and front cover mounting pattern.
With the Fleece FPE-LML-CP3-NP adapter and hardware, they physically bolt into place on an LML using the kit components.
Internal calibration and FCA behavior
LB7/LLY CP3s use an earlier regulator design with a different fuel flow vs current curve.
LBZ/LMM CP3s use the later regulator and calibration that tuners and conversion kits are built around, especially for higher rail pressure targets.
System pressure strategy
LB7/LLY platforms typically ran slightly lower stock rail pressure than LBZ/LMM and LML, but that’s largely ECM and injector-era specific.
LBZ/LMM pumps are proven at higher pressures and are the default base for performance variants (10mm “stroker” pumps, 42% / 85% over pumps, etc.).
What people are actually using in their trucks
Most LML CP3 conversions in the field use:
A stock LBZ or LMM Bosch CP3, or
An LBZ-based performance CP3 from brands like S&S, Exergy, Industrial Injection, etc.
LB7/LLY pumps are commonly reused when available, but reputable builders typically install an LBZ/LMM regulator and then tune for that combination.
Here’s how you can present it to your customers in the blog:
Pump: LBZ or LMM Bosch CP3 (stock or performance).
Regulator: LBZ/LMM FCA.
Kit: Fleece FPE-LML-CP3-NP hardware kit, plus appropriate tuning for your power goals.
This combination mirrors what Fleece ships in their complete FPE-LML-CP3-WP kit and what most tuners expect when they write LML CP3 conversion files.
Pump: Clean LB7 or LLY Bosch CP3.
Regulator: Upgrade to an LBZ/LMM FCA before installation.
Kit: Fleece FPE-LML-CP3-NP hardware kit, with custom tuning dialed in for an LBZ/LMM-style CP3.
This is ideal for customers who already own an early CP3 or have access to a good used unit and want to save money without sacrificing control or reliability.
Mixing an early LB7/LLY regulator with an LML CP3 conversion tune that expects an LBZ/LMM FCA.
Dropping in a random CP3 with an unknown regulator and assuming it will act like the pump in Fleece’s complete kit without data-logging or tuning support.
Encourage customers to verify desired vs actual rail pressure after the swap and to work with a tuner who understands CP3 conversions on LML trucks.
While the hardware-only FPE-LML-CP3-NP kit is great for custom builds, many owners are better served by a full, matched package.
The 2011–2016 LML CP3 Conversion Kit with CP3K Pump (FPE-LML-CP3-WP) includes:
All the same conversion hardware.
A new LBZ-based CP3K pump calibrated specifically for CP3 conversions.
Emissions-compliant, “no tuning required” operation when installed per Fleece’s instructions.
For customers who:
Don’t already own a good CP3,
Don’t want to mess with regulator swaps and calibration curve details, or
Want the most straightforward, reliability-focused upgrade from CP4 to CP3,
you can confidently steer them to the complete kit and then link your Bosch CP3 and FCA offerings for those who prefer or need individual components.
You must login to post comments.