Your compact tractor or mini excavator may wear any color of paint, but there is a good chance the engine under the hood says Yanmar TNV. On many of those engines, the injection pump is Yanmar’s own distributor-type MP pump.
When it starts acting up, it has a way of choosing the least convenient moment. It quits with a field to disc, a trench half dug or a storm on the way.
Start with the pump identification number and a service inquiry. Inspection findings determine which repairs and calibration steps are appropriate. Request a repair evaluation to discuss the unit before shipping.
Also Known As
- Yanmar MP pump, YPD-MP
- MP2 and MP4 versions
- Yanmar TNV injection pump
- 3TNV84, 3TNV88, 4TNV84 or 4TNV88 injection pump
- Mini excavator or compact tractor injection pump
- Yanmar numbers in the 729xxx-51xxx range
Did You Know? Yanmar was founded in Japan in 1912, and in 1933 it built what it calls the world’s first practical small diesel engine. Small diesels have been the company’s specialty ever since.
How the Yanmar MP Pump Works
Think of a paper route: one carrier, every house in order. A distributor-type pump uses one pumping section to build pressure and a distributor to deliver fuel to each cylinder in firing order, so one compact pump serves three or four cylinders.
- Supply. Fuel arrives from the lift pump and filter.
- Pumping. The pumping element builds injection pressure on each stroke.
- Distribution. The distributor routes each charge to the right cylinder.
- Control. The governor sets how much fuel each charge carries, and a solenoid cuts fuel when the key goes off.
Shop Talk: Distributor-type means one pumping section serves every cylinder through a distributor. An inline pump, like Yanmar’s YPES, gives each cylinder its own element. Different layouts, different rebuild procedures.
What It Fits
Yanmar TNV engines power machines sold under many brand names, so check the engine nameplate rather than the paint.
| Make and model | Engine | Years | Notes |
|---|---|---|---|
| Compact tractors, several brands | Yanmar 3TNV84, 3TNV88 | 729xxx-51xxx pump numbers seen on these engines | |
| Mini excavators, skid steers, gensets | Yanmar 4TNV84, 4TNV88 | 729xxx-51xxx pump numbers seen on these engines | |
| Mini excavators, loaders, gensets | Yanmar 4TNV98 | Later emissions versions may use common rail | |
| Some TNV82A and 88 engines | Yanmar TNV | Pumps numbered 719xxx-51xxx may be a different type; see YPES |
For engine-by-engine detail, see our Yanmar TNV engine page.
Part Numbers We See
Yanmar pump numbers read like 729xxx-51xxx. The first six digits identify the pump family and application, and the suffix after the dash identifies the specific version. Pumps numbered 719xxx-51xxx turn up on some TNV82A and 88 engines and may be a different type.
The pump label may also show the MP2 or MP4 type. Your machine’s builder may add its own part number, and the engine model and serial are on the engine nameplate.
Owner’s Tip: If your machine has a display or diagnostic port, note any fault codes before you pull the pump. A code for a sensor or solenoid can save you a pump removal.
Why MP Pumps Fail and the Symptoms
- Water from condensation and jobsite fuel rusts precision parts and can stick the pumping element.
- Dirt from dusty fills and overdue filters wears the pumping and distributor surfaces.
- Fuel cut solenoid failure gives you a machine that cranks and never fires.
- Governor wear brings hunting and droop under load.
- Seal leaks around the body and fittings.
- Long idle hours in gensets and excavators, which pile up pump hours without much work to show for it.
Symptoms:
- Hard starting or no start
- Low power with the bucket in the dirt or the loader full
- White smoke cold, black smoke under load
- Hunting at idle or steady rpm
- Fuel weeping around the pump
Not sure it is the pump? Our hard starting and smoke guide helps sort it out.
What We Do to Your Yanmar MP Pump
| Service option | Typical evaluation or service scope |
|---|---|
| Test and report | Bench test as received, written results, service recommendation |
| Rebuild and calibrate | Teardown, inspection, new seals and wear parts, solenoid check, calibration to spec, final test sheet |
| Exchange (when available) | Ask whether a compatible exchange unit is available and how the core process works |
Bench Notes: Distributor pumps do not forgive water. Rust on the pumping element or distributor surfaces can hang the pump, and the bench shows it as uneven or missing delivery to one or more cylinders.
What Model-Specific Verification Can Document
Evidence for Yanmar MP: When an approved procedure exists for this exact component, useful documentation can distinguish identification, visible condition, observed wear or contamination and supported functional test results. Record the assembly number and available engine data before deciding which checks will answer the reported complaint. Bench findings cannot replace the engine-side diagnosis. See how pump testing is evaluated.
Repair Options and Technical Considerations
For Yanmar MP, the available path follows what inspection actually finds—not a universal rebuild recipe. DCT reviews the component design, exact assembly number, contamination history and the applicable test procedure, whether the correct service parts and calibration information are available, and which work the customer chooses to authorize. Any exchange option is confirmed for the exact part rather than assumed from the family name. Explore how repair options are compared.
Appropriate work depends on the pumping-element, wear-part and solenoid condition. If a suitable new pump is unavailable, rebuilding the original may be worth evaluating. More in our rebuild scope guide.
How to Ship Your Yanmar MP Pump
- Photograph the pump label and the engine nameplate.
- Follow your engine service manual for removal and timing marks.
- Follow authorized de-fueling instructions and protect the ports with clean, suitable caps.
- Leave the fuel cut solenoid and linkage on the pump.
- Bag the pump and box it with two inches of padding on every side.
- Add your name, phone, machine model, hours and symptoms, then ship to the address provided during intake with tracking.
Ship It Right: Pad the solenoid and its connector. A snapped connector turns a straightforward rebuild into a parts hunt.
Full instructions are on our mail-in repair page.
Related Pumps and Parts
- Yanmar YPES: the inline pump on some Yanmar engines
- Zexel PFR: the plug-in pump on Kubota and Shibaura compacts
- Every Yanmar pump
- Injector repair and how bench testing works
FAQ
Is my pump an MP or a YPES?
Check the label and number. The MP is distributor-type; the YPES is inline. If you are not sure, send photos first. See our YPES page.
My machine is not branded Yanmar. Is this still the right page?
Possibly. Many compact tractors, mini excavators and skid steers use Yanmar TNV engines. Check the engine nameplate for a TNV model.
What is the difference between MP2 and MP4?
MP2 and MP4 are distinct designations within the Yanmar MP range. Use the complete pump number and engine identification to confirm the correct configuration; do not assume interchangeability from the short family name.
How fast will I get it back?
Before shipping, send the pump identification number and any project-specific requirements through the request a repair evaluation.
Small engine, big job list. Send in the MP pump and get your compact iron back to work. Start a Mail-In Repair or request a repair evaluation.