Best CP3 Conversion Kit — LML Duramax, 6.7 Cummins, 6.7 Powerstroke

September 4, 2026

Best CP3 Conversion Kit — LML Duramax, 6.7 Cummins, 6.7 Powerstroke

TL;DR: A CP3 conversion kit replaces the Bosch CP4.2 high-pressure fuel pump — the one that self-destructs and sends metal through the entire fuel system — with the older, far more tolerant Bosch CP3. It is the only permanent fix; disaster-prevention filters only limit how far the debris travels. For a stock-to-tuned truck on any of the three platforms, a stock-flow CP3 conversion kit from a known builder is the right buy, and the deciding factor between brands is not the pump — most start from the same Bosch core — but what the kit includes and how it handles pump control. Step up to a 10 mm or 12 mm stroker CP3 only if you are already past the fuel ceiling with larger injectors and a turbo to match.

If you own a 2011-2016 LML Duramax, a 2011-and-newer 6.7L Powerstroke, or a 2019-and-newer 6.7L Cummins HO, you are running a CP4.2. This guide is about picking the kit that gets it off your engine.

What a CP3 conversion kit actually replaces

The CP4.2 is a two-piston pump whose cam followers ride directly on a hardened cam lobe. In North American ULSD that interface can run marginal on lubrication, the follower scuffs its bore, and the pump begins shedding metal into the high-pressure side — downstream of every filter you own. From there it reaches the rail, the injectors, the return circuit, and the tank. There is no partial repair: a grenaded CP4 is a full fuel-system replacement.

The CP3 that preceded it is a three-piston pump with a different drive geometry and a long field record on the LB7 through LMM Duramax and the 2003-2018 Cummins common-rail trucks. It is not indestructible, but its failure mode is normally a graceful loss of pressure rather than a metal-shedding event.

A conversion kit bridges the two. At minimum it has to solve four problems:

Mounting — the CP3 has a different case and mounting flange than the CP4 it replaces.
Drive — the pump gear, drive coupler, or shaft has to mate to the engine's existing accessory drive.
Plumbing — a new high-pressure line from pump to rail, plus feed and return connections that match the CP3's fittings.
Control — the ECM has to command fuel volume through the CP3's metering valve instead of the CP4's, and read rail pressure correctly.

Problem 4 is where kits genuinely differ, and it is the one most buyers underestimate.

The three platforms are three different jobs

Do not assume a kit crosses platforms because the pump inside the box is the same. Bracketry, drive, lines, and control strategy are all platform-specific.

Platform	Years with CP4.2	Conversion difficulty	Control approach	Notes
Duramax 6.6 LML	2011-2016	Moderate — front-cover access, gear-driven	Custom ECM calibration, or kit-supplied controller	Most mature conversion on the market; deepest kit selection
Cummins 6.7 HO	2019 onward (confirm exact model-year cutoffs)	Moderate	Calibration or plug-in controller, depending on kit	Newest of the three; confirm emissions-equipment retention
Ford 6.7 Powerstroke ("Scorpion")	2011-present	Highest — tighter packaging, more disassembly	Typically a supplied controller module	Fewest kit options; verify year-split hardware

The LML has the deepest aftermarket because it has had the longest to mature. The 6.7 Powerstroke conversion is the most labor-intensive of the three, and it is the one where a shop quote is most likely to make sense over a driveway install.

Shop by platform: Duramax fuel system parts · Cummins fuel system parts · Powerstroke fuel system parts

What a complete kit has to include

Kits are sold at wildly different completeness levels, and the cheap one is usually cheap because it assumes you already own half of it. Use this as your checklist before you buy — every "no" is a part you will be sourcing mid-job with the truck apart.

Component	Why it matters	Commonly omitted?
CP3 pump (new or reman)	The whole point of the kit	No
Mounting adapter / bracket	The CP3 case does not bolt to a CP4 location unaided	No
Drive gear or coupler	Matches the CP3 shaft to the engine's drive	Sometimes sold separately
High-pressure line, pump to rail	CP3 outlet position differs	Sometimes
Feed and return adapters and fittings	CP3 inlet and return threads differ	Frequently
Pump control: calibration credit or controller module	Without it the truck cannot manage rail pressure	Frequently
CP4 port block-off / rail plug where applicable	Seals the old circuit	Sometimes
O-rings, seals, front cover gasket	One-time-use parts you will disturb	Frequently
Instructions with torque values	The pump gear nut torque is not a guess	Varies by brand

A kit that omits both the control solution and the fittings is not a conversion kit — it is a pump with a bracket.

Pump flow tier: stock, 10 mm, or 12 mm stroker

The CP3 is sold in stock displacement and in modified "stroker" versions with larger pumping elements, usually marketed as 10 mm and 12 mm. More displacement means more fuel volume at a given rpm, which matters only when your injectors and turbo can use it.

Pump tier	Typical use	Pairs with	Caution
Stock-flow CP3	Stock to tuned, towing, daily driver	Stock or mild injectors	The correct choice for the large majority of conversions
10 mm stroker	Built truck, larger injectors, bigger single turbo	Oversized injectors, upgraded lift pump	Requires supply-side flow to keep up
12 mm stroker	High-horsepower and competition builds	Large injectors, compounds	Overkill on a stock-injector truck; adds parasitic drag

The mistake that costs the most is buying a stroker pump to fix what is actually a supply-side problem. A high-flow CP3 starved by a marginal lift pump and a restrictive filter head will cavitate and wear early. Get the lift pump and fuel filtration right first — that is the most common reason a converted truck still throws a rail-pressure code.

Horsepower figures attached to these tiers vary enormously with injector size, turbo, and calibration, so treat any published "supports X hp" claim as marketing rather than a specification.

Brand comparison — what actually separates the kits

Most conversion kits start from a Bosch CP3 core. What you are choosing between is the builder's remanufacturing standard, the completeness of the hardware, the control solution, and the support you get at 11 p.m. with the truck in pieces.

Brand	Platforms in our catalog	Positioning	Best for
Industrial Injection	LML, 6.7 Cummins HO, 6.7 Powerstroke	Broadest platform coverage; also offers 12 mm stroker CP3s across the CP3-era trucks	Buyers who want one brand for the conversion and a later fueling upgrade
Exergy Performance	LML, 6.7 Cummins HO, 6.7 Powerstroke	Fuel-system specialist; strong injector-and-pump matching	Builds where injectors and pump are specified together
Fleece Performance	LML, 6.7 Cummins HO	Known for the Cheetah and PowerFlo CP3 line on CP3-era trucks	Cummins and Duramax owners already running Fleece fueling
Bosch (reman CP3)	LB7, LLY, LBZ, LMM, 5.9/6.7 CR, 6.4 Powerstroke	OE pump — not a conversion kit	Replacing a worn CP3 on a truck that already has one

Two practical notes. First, a Bosch reman CP3 is not a conversion kit — it is the correct part for a CP3-era truck whose original pump wore out, and ordering one for an LML leaves you without the bracket, gear, lines, or control. Second, our Fleece coverage currently spans LML and 6.7 Cummins HO but not the 6.7 Powerstroke, so a Ford owner is effectively choosing between the Industrial Injection and Exergy kits. Confirm current Fleece Powerstroke availability at time of order.

Browse the full pump and kit range in fuel injection, and size injectors in fuel injectors.

The control question — calibration, module, or neither

This is where conversions go wrong after the wrenching is done.

The CP4 and the CP3 meter fuel differently, and the ECM has to be told. Broadly there are two paths:

ECM calibration. A custom tune rewrites the pressure-control strategy for the CP3. It is the cleanest technical solution and it lets a tuner correct anything else the truck needs at the same time. It requires a tuner who has done this platform before.
Kit-supplied controller module. A standalone box translates the pump command signal so the factory calibration can stay in place. This is the common approach where retaining the stock emissions calibration matters, and it is why the Ford kits in particular tend to ship hardware rather than a tune credit.

Ask the seller which path their kit uses before you buy. If the answer is a calibration, confirm your tuner supports it on your model year and emissions configuration.

One point that gets muddled in forum threads: a CP3 conversion is a fuel pump swap, not an emissions delete. Done correctly it retains the DPF, EGR, and SCR hardware and leaves the emissions calibration intact. Kits bundled with emissions-equipment removal are a different product carrying different legal exposure, and the two are not interchangeable.

If the CP4 already failed

If the pump has already come apart, a conversion kit alone is not the repair. Metal that has passed through the rail is in the injectors, the lines, and the return circuit, and anything left behind will find its way into the new pump.

A post-failure job realistically includes:

High-pressure pump replaced with the CP3 conversion.
All injectors replaced — not cleaned, not reused.
Fuel rail replaced, or fully flushed and verified.
High-pressure injection lines replaced.
Return lines flushed or replaced.
Tank dropped and cleaned, in-tank module inspected.
Filters and filter housing replaced.
Lift pump inspected — debris travels backward through the return.

Skipping any of these is why "I did the conversion and it failed again" threads exist.

How to install a CP3 conversion kit — the sequence that matters

Torque values and step detail come from your kit's instructions. This is the order of operations that keeps the job from doubling.

Confirm the kit matches the truck — platform, model year, emissions configuration. Verify the control path (calibration vs module) is in hand before any disassembly.
Relieve fuel system pressure and disconnect the batteries. Common-rail pressure is dangerous; do not shortcut this.
Clean the work area obsessively. Diesel fuel systems fail from contamination introduced during service more often than owners believe.
Remove the CP4 per platform procedure, capturing the drive gear or coupler. Inspect the removed pump for scoring — if it shows debris, escalate to the post-failure procedure above.
Inspect for contamination before installing anything new. Cut the old filter open. Look inside the rail.
Fit the adapter bracket and CP3, torquing the gear nut and mounting hardware to the kit's published values.
Route the new high-pressure and supply lines, keeping every fitting capped until the moment of connection.
Install the controller or load the calibration.
Prime, then leak-check at low pressure before the first start.
Start and watch live rail pressure and fuel-rail-pressure deviation, then re-check every fitting warm.

Which kit to buy

Stock or tuned LML you plan to keep — a stock-flow CP3 conversion kit, complete with a control solution. All three brands in our catalog are defensible; pick on kit completeness for your model year.
LML getting injectors soon — buy pump and injectors from one fuel-system specialist so the sizing is matched.
2019+ 6.7 Cummins HO — stock-flow conversion; verify the model-year hardware split before ordering.
6.7 Powerstroke — expect a controller-based kit and budget the labor honestly. This is the conversion most worth handing to a shop.
Already grenaded, any platform — conversion kit plus injectors, lines, rail, and tank service. Treat the entire fuel system as contaminated.
CP3-era truck (LB7-LMM, 5.9/early 6.7 CR, 6.4 PSD) — you do not need a conversion. A Bosch reman CP3 or a performance CP3 is your part.

Frequently asked questions

Does a CP3 conversion void my factory warranty? It can affect coverage on related components. Under US law a manufacturer generally has to show the aftermarket part caused the failure to deny a claim, but a fuel-system claim on a converted truck is exactly the argument you do not want to be having. If the truck is still under powertrain warranty, weigh a disaster-prevention setup until it expires.

Is a CP4 disaster-prevention kit good enough on its own? No. Those kits reroute or filter debris so a failing pump does not take the injectors with it. That is real value — it turns a full fuel-system replacement into a pump replacement — but the CP4 is still on the engine and can still fail. Prevention limits the damage; conversion removes the cause.

Will a CP3 conversion make more power? Not by itself. A stock-flow CP3 restores capability rather than adding it. Power comes from injectors, turbo, and calibration. A stroker CP3 removes a fuel-volume ceiling on a truck that has already reached one.

Can I install a CP3 conversion kit without tuning? Only if the kit includes a controller module that handles pump command translation. Verify this before you buy — a kit advertised as "no tune required" should state explicitly what hardware provides that.

Does the conversion pass emissions inspection? A properly done conversion retains all emissions hardware and calibration, so it does not by itself create an inspection failure. Visual inspection regimes vary by state, and any accompanying calibration must not alter emissions strategy. Check against your state's current inspection criteria.

Do I need to upgrade the lift pump at the same time? Strongly recommended on any converted truck, and effectively mandatory with a stroker CP3. Supply-side restriction is the fastest way to wear out a brand-new high-pressure pump.

Should I replace injectors while I am in there? If the CP4 failed, yes — non-negotiable. If the pump is intact and you are converting preventively, no, unless the injectors are already due on age and mileage.