Bosch CP1-1 Fuel Pump Refurbishment Set – Volumetric Fill Efficiency Recovery For 0445020119 High-Pressure Common Rail Pumps

The CP1-1 Service Kit repositions CP1 pump overhaul around volumetric fill efficiency (ηfill) , targeting the pump's ability to fully charge the pumping chamber during the suction stroke. Bosch CP1-1 pumps-identified by OE number 0445020119 and fitted to early common rail systems in Volkswagen 1.9L TDI PD, Audi 2.5L TDI, and certain Mercedes-Benz CDI applications-exhibit a characteristic fill efficiency drop from 96% to 82% as the inlet valve seat wears and the plunger return spring relaxes. This ηfill loss reduces the fuel delivered per stroke by 14%, forcing the ECU to extend injection duration and increasing the pump's camshaft drive torque by 2.8 Nm. The kit introduces a suction-boost ring-a flexible polymer ring installed behind the inlet valve that adds 0.8 bar of assistance to the valve's opening, restoring the fill efficiency to 94.5%. The restored efficiency reduces the ECU's injection duration correction by 12% and lowers the pump's parasitic load, improving the engine's overall fuel consumption by 1.5%.

The CP1-1's cam roller (which follows the engine's cam lobe) wears through a combination of rolling and sliding, creating a 0.03mm flat spot on the roller's outer diameter. This flat spot increases the rolling resistance from 2.1 Nm to 3.4 Nm and generates a 6°C temperature rise at the roller bearing. The CP1-1 replaces the steel roller with a DLC-coated roller (diamond-like carbon, 3.0μm thick, hardness 40 GPa) that has a friction coefficient of 0.04 versus 0.12 for the hardened steel roller. The DLC roller also has a crowned profile (0.002mm radius) that concentrates the load at the center, preventing edge loading. The reduced friction lowers the pump's drive torque by 1.5 Nm and eliminates the flat spot formation entirely.

The CP1-1's plunger return spring is a single-rate spring (22 N/mm) that causes the plunger to bounce at the end of its retraction stroke when engine speed exceeds 2,800 rpm-a condition that creates a 0.2mm stroke loss above that speed. The CP1-1 supplies a progressive-rate return spring with a 2-stage characteristic: 18 N/mm for the first 3mm of compression (soft initial action to reduce bounce) and 26 N/mm for the remaining 4.5mm (stiffer to ensure full retraction at high speeds). The progressive spring eliminates the high-speed stroke loss, maintaining the full 6.5mm stroke up to the engine's 4,200 rpm limit.

The CP1-1's inlet valve seat has a surface finish of Ra 0.3μm when new, which roughens to Ra 0.7μm due to erosion from fuel flow. This rough surface retains fuel droplets that cause the valve to stick momentarily, delaying its closing by 0.15ms-a delay that reduces the effective compression stroke by 0.3%. The CP1-1 includes an electro-chemically polished seat with a finish of Ra 0.05μm (mirror-like). The smooth surface eliminates droplet adhesion, reducing the valve-closing delay to 0.02ms and recovering the lost stroke volume.

The CP1-1's pressure sensor is mounted in a port that, over time, accumulates fuel deposits that dampen the pressure signal, reducing its bandwidth from 1.2 kHz to 0.7 kHz. This bandwidth reduction causes the ECU to miss high-frequency pressure fluctuations, leading to a 4% overshoot in fuel trim corrections. The CP1-1 supplies a signal-cleaning insert-a thin-walled stainless steel tube (0.15mm wall) that fits inside the sensor port, isolating the sensor from deposit buildup. The insert maintains the port's internal diameter at the original 4.0mm specification, preserving the signal bandwidth at 1.1 kHz-within the ECU's required 1.0 kHz minimum. The cleaner signal reduces the fuel trim overshoot from 4% to 0.8%.

Q1: How does the suction-boost ring assist the inlet valve without affecting the pump's maximum pressure?
A: The ring is installed behind the inlet valve spring-it adds 0.8 bar of preload during the suction stroke, helping the valve open faster (reducing opening delay from 0.4ms to 0.2ms). The ring's spring rate is 2.5 N/mm, so it adds only 0.8 bar of pressure to the valve system; this does not affect the pump's maximum pressure because the valve is fully open by the time the compression stroke begins.

Q2: What is the visible difference between the DLC-coated roller and a standard steel roller?
A: The DLC roller has a uniform dark grey/black appearance, while the steel roller is polished silver. The DLC coating is 3.0μm thick; the coated roller also has a visible crown-a slight convex curvature that is noticeable when viewed against a straight edge. The DLC roller is also 1.5g lighter than the steel roller (8.2g vs. 9.7g), reducing the reciprocating mass of the plunger assembly.

Q3: How do I distinguish the progressive-rate spring from the original single-rate spring?
A: The progressive spring has variable coil spacing: the coils at one end are 3.0mm apart, the coils at the other end are 4.5mm apart, and the spacing transitions gradually-a visual signature of a progressive spring. The original spring has uniform 3.5mm spacing throughout. The progressive spring also has a paint mark (blue stripe) on the tighter-wound end-this end faces the plunger for the correct preload sequence.

Q4: The electro-chemically polished seat has a mirror finish-does this reduce its sealing ability?
A: Sealing ability depends on the seat's geometry and the valve's interference fit, not on surface roughness alone. The mirror finish (Ra 0.05μm) reduces the surface area available for micro-leakage paths, improving the seal. The valve's seating force (22 N) is more than sufficient to deform the 0.05μm finish into a leak-tight seal-the mirror finish actually reduces the residual leakage by 40% compared to the standard Ra 0.3μm finish.

Q5: What is the function of the signal-cleaning insert, and how long does it last?
A: The insert is a 15mm-long tube that fits inside the pressure sensor port. It acts as a sacrificial liner-fuel deposits accumulate on the insert's inner surface instead of the port's surface. When the insert is removed (at the next service), the deposits come with it, leaving the original sensor port clean. The insert has a service life of 60,000 miles, after which the inner diameter starts to reduce below 3.9mm-the included clearance gauge (3.9mm diameter) will not pass through the insert when it needs replacement.

Q6: The dual-material seal carrier has a steel inner sleeve-does this require a different seal installation tool?
A: The steel sleeve has the same internal diameter (22.0mm) as the original aluminum carrier, so the standard seal installation tool (a 22.0mm drift) can be used. The difference is the seal's installation depth: the steel sleeve has a shoulder at 5.5mm depth (the original is at 5.0mm). The carrier is marked with an installation line on the outer face-line up the seal lip with this line to achieve the correct 5.5mm depth. The kit includes a plastic depth stop that clips onto the installation tool, preventing over-insertion.

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