Yanmar 2TNV70, 3TNV70 & 3TNV76 fuel system, injectors and starting
A Yanmar 2TNV70, 3TNV70 or 3TNV76 that starts poorly or runs irregularly has the problem in nine out of ten cases in the fuel system or the glow plug system. In this blog we explain how the system works, how to bleed it, what the factory values are for injectors and injection timing, and how to systematically approach a cold-start problem.
Suitable for the entire series: Yanmar 2TNV70, 3TNV70 and 3TNV76 (Komatsu 2D70E, 3D70E, 3D76E) — all indirect injection (IDI) with swirl chamber.
Yanmar TNV fuel system: the layout
From the tank, the diesel flows via the fuel filter with water separator (and on many versions an electric feed pump) to the mechanical inline injection pump. This pumps the fuel via the high-pressure lines to the injectors, which spray into the swirl chambers at 11.8–12.8 MPa opening pressure. Excess fuel returns to the tank via the return line. A stop solenoid on the pump shuts off the fuel supply when you switch off the ignition.
Use clean diesel fuel according to EN 590 (or equivalent); water and dirt are the biggest enemies of the pump and injectors. Drain the water separator every 50 hours and replace the fuel filter every 500 hours — see Yanmar TNV maintenance. Replace rubber fuel hoses every 2 years or 2000 hours, even if they still look fine.
Bleeding the Yanmar TNV fuel system
Bleeding is necessary before the first start, after running out of fuel and after any intervention on the system (replacing the filter, draining the water separator, disconnecting a line). On versions with an electric feed pump, it's simple: turn the ignition to "ON" for 10–15 seconds — the pump then bleeds the system itself. Then start as normal. If air remains in the system (engine stalls, runs irregularly), check for leaking lines and a clogged mesh filter in the water separator (OEM 171081-55910).
Yanmar TNV injectors: values and replacement
| Component | Value |
|---|---|
| Injector opening pressure | 11.8–12.8 MPa (120–130 kgf/cm²) |
| Injector tightening torque in head | 39.2 N·m (do not oil thread) |
| Nozzle holder union nut | 49–53 N·m |
| High-pressure line unions | 29–34 N·m |
| Inspection interval | Inspect, clean and test every 1500 hours |
Symptoms of worn injectors: hard knocking (rattling sound), black smoke under load, increased fuel consumption, poor cold starting and irregular idling. A poor spray pattern or too low an opening pressure means overhaul or replacement is needed. We supply complete injectors for the 3TNV76 (SKU-47058-s), complete injectors 3TNV70–3TNV76 (SKU-47042-s) and individual nozzles (SKU-47059-s).
Yanmar TNV injection timing
Injection timing is checked using the spill-timing method on cylinder 1 and differs per rated speed version (BTDC ± 1°): 15° at 2000–2100 rpm, 16° at 2200 rpm, 18° at 2300–3000 rpm and 20–21° for the 3000–3600 rpm versions. Adjustment is done with shims under the injection pump — precision work; the full procedure is in chapter 7 of the workshop manual, which we also supply as a booklet (VAR-0094).
Yanmar TNV glow plugs and cold starting
As an IDI engine, the TNV series needs working glow plugs — the pre-glow system glows for about 3 seconds by default (longer in freezing conditions, depending on the machine version; some machines also have an intake air heater on the manifold). If the engine starts poorly when cold, work through this checklist:
| Step | Check |
|---|---|
| 1. Glow plugs | 12V on the plugs during pre-glow? Measure the resistance of each plug (± 1 Ω; open circuit = defective). One faulty plug on a 3-cylinder is immediately noticeable. |
| 2. Glow relay | No voltage on the plugs → test the relay and wiring. |
| 3. Fuel supply | Filter full, water separator drained, system bled, feed pump audible? |
| 4. Stop solenoid | Does the solenoid click audibly when the ignition is turned "ON"? If not: replace the fuse, wiring or solenoid. |
| 5. Starter motor and battery | Slow cranking = poor battery, ground connection or starter motor; the engine needs to turn over briskly for a good start. |
| 6. Compression | Still starts poorly with working glow plugs and fuel supply? Measure compression (see overhaul blog). |
The right parts for this: glow plug OEM 129155-77800 (SKU-551216) — fits the 2TNV70, 3TNV70 and 3TNV76 —, glow relay Yanmar TNM/TNV (SKU-123003), stop solenoid (SKU-98002), electric feed pump (SKU-56013) or mechanical feed pump 3TNV76 (SKU-56007), starter motor (SKU-129044) and alternator (SKU-1200013).
Practical tip: on a 3-cylinder engine, always replace all three glow plugs at the same time. If one has failed, the other two usually follow soon after — and for the price of a glow plug (SKU-551216) it's not worth the risk.
