Bosch CP3-1 Fuel Pump Service Kit – Flow Continuity Restoration Assembly For 0445020137 Radial-Piston Common Rail Pumps

The CP3-1 Service Kit repositions CP3 pump overhaul around flow continuity, measuring the pump's ability to maintain a seamless fuel flow as the three plungers transition between their pumping cycles. Bosch CP3-1 pumps-identified by OE reference 0445020137 and used in Ford Transit 2.2L/2.4L, PSA 2.2L HDI, Volvo D5, and certain Fiat/Opel common rail engines-exhibit a characteristic "flow dip" at the intersection point where one plunger finishes its stroke and the next begins. This dip, which becomes 8% deeper as the plunger seals wear, creates a 0.3ms pressure drop at the rail that the ECU cannot fully compensate for. The CP3-1 introduces a flow-smoothing accumulator-a spring-loaded piston chamber that stores energy during the pressure peak and releases it during the dip, reducing the intersection pressure drop from 18 bar to 3 bar. The restored flow continuity eliminates the "hesitation" felt during part-throttle operation.

The CP3-1's cam ring develops an end-runout (axial wobble) of up to 0.06mm due to thrust bearing wear, causing the three plungers to have slightly different stroke lengths (varying by 0.15mm). The CP3-1 supplies a runout-correction shim set-three shims (0.03mm, 0.06mm, 0.09mm thickness) that install under the cam ring's retaining plate, compensating for the measured runout. The correct shim is selected using the included dial indicator that measures the runout at the cam ring's outer face; restoring the end-runout to below 0.01mm equalizes the plunger strokes, reducing the plunger-to-plunger flow variation from 4% to 0.5%.

The CP3-1 plunger guides are steel bushings that suffer from oil film breakdown at high loads. The CP3-1 replaces them with porous bronze guides-sintered bronze with 22% porosity, impregnated with a high-temperature oil (silicone-based, 180°C rating). The pores act as a reservoir, releasing oil during the high-pressure stroke and re-absorbing it during the suction stroke. The porous guide maintains a lubricating film even during the pump's peak pressure phase (1,800 bar), reducing the plunger friction coefficient from 0.08 to 0.035.

The CP3-1 inlet throttle has a non-linear flow coefficient curve-the Cv changes from 0.52 at low plunger speeds to 0.68 at high plunger speeds, creating a 30% fill variation as engine speed changes. The CP3-1 includes a linearized inlet throttle with a contoured plunger profile (15° taper) that maintains a Cv of 0.60 ±0.02 across the entire 800–4,000 rpm range. The linearized throttle eliminates the speed-dependent fill variation, ensuring consistent plunger filling from idle to high speed.

The CP3-1's O-rings exhibit high static friction ("stiction") that causes the plunger to start its stroke with a 2.5 Nm torque spike-a spike that contributes to the camshaft's torsional vibration. The CP3-1 supplies low-stiction O-rings with a 0.02mm PTFE skin and a 5° angled lip profile. The PTFE skin reduces the static friction coefficient from 0.4 to 0.08, and the angled lip provides a smoother transition to dynamic friction. The reduced stiction eliminates the starting torque spike, lowering the pump's drive torque fluctuation by 1.5 Nm.

Q1: How does the flow-smoothing accumulator store and release energy without creating a pressure lag?
A: The accumulator's piston is pre-loaded to 300 bar, which is below the pump's minimum operating pressure (350 bar at idle). The piston moves (compressing the spring) only when the pump pressure exceeds 350 bar, storing energy during the pressure peak and releasing it during the intersection dip-a process that takes 0.5ms, well below the pump's 2.0ms pumping cycle.

Q2: What is the correct procedure for selecting the runout-correction shim?
A: Install the dial indicator with the probe touching the cam ring's outer face. Rotate the pump shaft slowly-the indicator shows the total runout (TIR). For a TIR of 0.06mm, use the 0.09mm shim; 0.04mm TIR uses 0.06mm shim; 0.02mm TIR uses 0.03mm shim. The shim is installed under the retaining plate-it does not affect the cam ring's axial position relative to the plungers.

Q3: The porous bronze guides are impregnated with silicone oil-does this oil mix with the diesel fuel and affect combustion?
A: The silicone oil (20ml total per guide) remains within the pores and is not released into the fuel-it acts as a boundary lubricant, never entering the combustion chamber. The oil is sealed by the plunger's O-ring, so no mixing occurs. The silicone is also diesel-compatible; if a small amount did migrate, it would pass through the system and burn without residue.

Q4: What is the visual difference between the low-stiction O-rings and standard O-rings?
A: The low-stiction O-rings have a thin white PTFE skin visible as a dull coating on the surface. Standard O-rings are uniformly black. The low-stiction rings also have a slight lip profile-a raised edge on the inner diameter-that is visible under a magnifying glass. The PTFE skin is 0.02mm thick and reduces the ring's stiction from 2.5 N to 0.3 N.

Q5: The acoustic-damping insert is a porous ceramic plug-does it restrict the pressure sensor's response time?
A: The plug is 50% porous with 20μm interconnected pores, so it does not block pressure waves-it only dampens the acoustic resonance at 1.5 kHz. The sensor's response time (0.2ms) is unchanged because the pressure wave travels through the pores without restriction. The plug is placed at the bottom of the sensor port, not in the pressure path-it only affects the standing waves within the port.

Q6: This CP3-1 kit is listed for 0445020137-does it fit the CP3-1 pump with a black plastic cover (used in some Ford Transits)?
A: Yes-the black plastic cover is a styling variation and does not change the pump's internal dimensions. The CP3-1 kit fits all 0445020137 pumps regardless of the cover material. The kit's housing gaskets are designed for both cover types. The only distinction is the torque setting: plastic cover models use 35 Nm on the cover bolts (versus 45 Nm for metal covers)-the kit's torque card lists both values.

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