Part of the Yanmar Repair Manuals.
An injection pump rebuild stalls the moment you need a number nobody posts online: the plunger diameter, the delivery valve pressure drop time, the torque on the governor weight nut. This Yanmar service manual (publication M9961-03E080) settles those questions for YPES-ML series fuel injection equipment, whatever engine the pump came off.
Across 65 pages it works through the fuel supply system, then full disassembly, inspection, and reassembly of the injection pump and governor, followed by bench adjustment: injection timing, plunger and delivery valve pressure tests, and injection volume balancing across cylinders. Separate chapters handle the fuel feed pump and the injection nozzles, including washing, inspection, and opening pressure adjustment.
The PDF downloads immediately after purchase, with 61 bookmarks, so you can jump from a sticking plunger straight to the inspection limits and torque figures you need before the pump goes back together.
What's Inside This Yanmar YPES-ML Manual
| System | Pages | Key Topics |
|---|---|---|
| Introduction | 2 | |
| for Safe Servicing | 6-8 | Warning Symbols, Safety Precautions |
| Fuel Supply System | 9-21 | Fuel Injection Pump Construction, Fuel Injection Pump Specifications, Fuel Injection Pump, Injection Volume Control, Governor Construction |
| Disassembly, Reassembly and Inspection of Governor and Pump | 22-36 | Governor Disassembly, Inspection of Governor, Disassembly of Fuel Injection Pump, Inspection of Fuel Injection Pump, Assembling Governor |
| Adjustment of Fuel Injection Pump and Governor | 37-49 | Preparations, Top Clearance, Of Injection Timing, Plunger Pressure Test, Delivery Valve Pressure Test, Injection Volume (Measuring Injection Volume) |
| Fuel Feed Pump | 50-52 | Fuel Feed Pump Specifications, Disassembly and Reassembly of Fuel Feed Pump, Fuel Feed Pump Inspection |
| Fuel Injection Nozzle | 53-59 | Functioning of Fuel Injection Nozzle, Type/Construction of Fuel Injection Nozzle, Fuel Injection Nozzle Disassembly, Fuel Injection Nozzle Inspection (Washing) |
| Troubleshooting | 60-62 | Troubleshooting of Fuel Injection Pump, Major Faults and Troubleshooting |
| Tools | 63-64 | Pump Mounting Scale, Measuring Device, Plunger Insert, Tappet Holder, Rack Indicator, Plunger Gauge |
| History of Revision | 65 | - |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Governor weight nut tightening torque | 68.6 - 73.5 N-m (7.0 - 7.5 kg-m) | p. 32 |
| Delivery holder tightening torque | 29.4-34.3 N-m (3.0-3.5 kgf-m) | p. 40 |
| Fuel filter element replacement | Disassemble and clean, or replace element | p. 60 |
| Fuel feed pump discharge volume | 230 cc/min at 1500 cam rpm, discharge pressure of 0.2 kg/cm² | p. 50 |
| Fuel feed pump closed off pressure | 0.3 kg/cm2 or more (at 400 cam rpm) | p. 50 |
| Stop solenoid replacement | Replace | p. 60 |
| Plunger diameter | 6 mm | p. 11 |
| Injection starting pressure (NP-Dnopd nozzle type) | 11.8 – 12.8 Mpa (120.3 – 130.5 kg/cm²) | p. 37 |
| Nozzle opening pressure (NP-Dnopd nozzle type) | 12.3MPa (125.4 kgf/cm2) | p. 54 |
| Injection pipe inner/outer diameter × length | Φ1.8/Φ6.0 × 500 mm | p. 37 |
| Injection pipe minimum bending radius | 25 mm | p. 37 |
Yanmar YPES-ML Common Problems This Manual Covers
Stuck plunger starves one cylinder
Water or debris in the fuel seizes a plunger in its barrel and that cylinder stops getting fuel. The disassembly chapter takes the pump apart in order, shows what to inspect on the plunger and barrel, and covers correct reassembly.
Manual Section: 3. Disassembly, Reassembly and Inspection of Governor and Pump p. 22Engine overspeeds or will not shut down
A worn or misadjusted governor lets the rack overfuel, and the engine runs away or refuses to stop cleanly. The adjustment chapter sets the fuel limit bolt, maximum speed limit bolt, and idling, and includes a check of injection stop.
Manual Section: 4. Adjustment of Fuel Injection Pump and Governor p. 37Hard starting until the fuel is bled
Air ingress or a weak feed pump starves the injection pump, and starting stays hard until supply is restored. The manual gives the feed pump discharge test, 230 cc/min at 1500 cam rpm, plus disassembly and inspection steps.
Manual Section: 5. Fuel Feed Pump p. 50Rough running from a dribbling nozzle
A fouled or worn nozzle dribbles instead of atomizing, causing sputter, smoke, and uneven power. The nozzle chapter covers washing, inspection against the 0.1 mm contact surface wear limit, and adjusting opening pressure on a tester.
Manual Section: 6. Fuel Injection Nozzle p. 53Uneven power across cylinders
When delivery volume drifts between elements, the engine hunts and pulls unevenly under load. The adjustment chapter shows how to measure injection volume per cylinder and bring each element back into uniformity.
Manual Section: 4. Adjustment of Fuel Injection Pump and Governor p. 37Cranks but gets no fuel
A no-start with good compression usually traces to the fuel side: clogged filter element, a stop solenoid that never opens, or a pump fault. The troubleshooting chapter charts these causes and the fix for each, including filter cleaning or replacement.
Manual Section: 7. Troubleshooting p. 60Frequently Asked Questions
What exactly does this manual cover?
Yanmar YPES-ML series fuel injection equipment: the fuel injection pump, governor, fuel feed pump, and fuel injection nozzles, from construction and specifications through disassembly, inspection, reassembly, and bench adjustment. It is Yanmar publication M9961-03E080, 65 pages, in English. It covers the fuel equipment itself, not the rest of the engine.
Does it include nozzle pressures and wear limits?
Yes. The Fuel Injection Nozzle section gives an opening pressure of 12.3 MPa for the NP-DNOPD nozzle, a 0.1 mm contact surface wear limit, nozzle nut torque, and a spray pattern check with a 5 to 10 degree cone angle. p. 53
Can I recalibrate the pump and governor with this manual?
The Adjustment of Fuel Injection Pump and Governor section covers preparations, injection timing, plunger and delivery valve pressure tests, injection volume measurement, and governor settings. The Tools chapter lists the pump mounting scale, rack indicator, and other calibration equipment the procedures call for. p. 37
Will it help diagnose a no-start or rough running?
Yes. The Troubleshooting section pairs symptoms such as no fuel delivery, hard starting, and uneven running with likely causes in the pump, feed pump, filter, stop solenoid, and nozzles, then points you to the repair procedure for each. p. 60
Is this Service Manual a digital download?
Instant PDF download. You get the full 65-page searchable Service Manual immediately after payment. Open it on your laptop, tablet, or phone right in the shop.
Am I able to print pages from this manual?
Yes. The PDF has no DRM restrictions, so print any page or section you need for your shop. Works with any standard printer.
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