146402-4720 Denso Fuel Pump – Low‑Pulsation Delivery for Stable Rail Pressure in Japanese Common Rails

Q1: How does the 146402‑4720 differ from the 146402‑4710?
The 4710 is an earlier HP4 pump with a smaller displacement (105 L/h) and a single‑stage damper; the 4720 has increased flow (120 L/h) and the dual‑stage damper, providing lower pulsation. They are physically similar, but the 4720 requires a different ECU map (higher flow offset) and the SCV calibration code is not interchangeable-using a 4720 on a 4710‑calibrated engine will over‑fuel and may trigger a pressure relief valve opening.

Q2: Can I replace only the pump and keep the old injectors?
Yes, but we recommend checking the injector leak‑off volume; if the old injectors have high leakage (>8 mL/min at idle), they will cause the pump to work harder, reducing its efficiency retention. Also, old injectors may have worn internal components that create pressure waves, increasing the rail ripple-potentially negating the low‑pulsation benefit of the new pump. Ideally, replace injectors within the same service interval.

Q3: What is the expected service life of this pump in a city bus with frequent idling?
The plunger wear is the primary life‑limiter; in severe duty (long idle periods, high ambient temperature), expect 400,000–450,000 km before volumetric efficiency drops below 85% (the threshold for noticeable pressure instability). In highway service, life reaches 600,000 km. Using clean fuel (5‑µm filtration) and changing the fuel filter every 30,000 km are critical-abrasives directly erode the DLC coating.

Q4: Why does my rail pressure fluctuate after installing a new pump, even with the correct SCV code?
Fluctuation often indicates air in the system-prime the pump thoroughly using the hand primer until solid fuel flows from the return line. Also, check the SCV connector for a loose pin; a poor connection can cause intermittent current, leading to erratic SCV response. Finally, verify the timing alignment-a misaligned cam plate creates asymmetric plunger lifts, generating uneven pulsations that the damper cannot fully cancel.

Q5: Can this pump operate with biodiesel (B20) without accelerating plunger wear?
Biodiesel's lower lubricity can increase the friction coefficient, but the DLC coating provides good protection. However, biodiesel's higher viscosity increases the feed pump load and may raise the inlet restriction-ensure the fuel filter is rated for B20. We also recommend adding a lubricity enhancer (e.g., 2% biodiesel‑compatible additive) to restore the wear protection. With these precautions, the pump life is similar to that with standard diesel.

Q6: How can I monitor the pump's pulsation performance without specialized equipment?
You can listen for combustion noise-a well‑damped pump produces a smooth, even engine note, while excessive pulsation often creates a "knocking" or "rattling" sound that varies with load. Also, monitor the ECU's "Rail Pressure Actual vs. Desired" deviation; a stable deviation within ±10 bar indicates good pulsation damping. Additionally, the "SCV Duty Cycle" parameter should remain steady at a given load; if it fluctuates widely, the pump is compensating for internal leakage or pulsation feedback-early signs of wear.