Engine Won't Restart Hot After Field Work
A 4-cylinder diesel utility tractor stalls after two hours of slashing on a 32 °C day and will not restart. The operator reports it 'just died' with no warning, then cranked until the battery went flat. On arrival the engine is hot, the fuel tank is half full, and the primer bulb feels firm. The fuel filter was replaced 80 hours ago. There is fuel at the injector bleed screw when cranked. The engine turns over freely on a boost but does not fire; there is no smoke from the exhaust while cranking. The operator has a spare fuel filter and tools but no diagnostic equipment beyond a multimeter. The paddock must be finished today because rain is forecast.
1. Distinguish between the likely causes of a hot no-start with no exhaust smoke, and explain what the absence of smoke tells you about fuel delivery.
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No exhaust smoke during cranking means little or no fuel is being burnt. That narrows the fault to the fuel injection side rather than compression or air supply, because a compression failure or blocked intake would usually still produce some unburnt fuel smoke once fuel is delivered.
Key candidates:
- Fuel supply restriction causing low injection pressure: blocked tank strainer, collapsed hose liner, or a filter that is partially blocked despite recent replacement (possible contamination or wrong filter).
- Air ingress in the low-pressure side, though the firm primer bulb argues against a large air leak.
- Injection pump solenoid or fuel shut-off fault: if the stop solenoid is not energised, no fuel reaches the injectors. This matches a sudden stall and no smoke.
- Failed lift pump or a failed injector pump drive.
What the evidence supports: the engine died suddenly rather than losing power gradually, and there is fuel at the bleed screw. A gradual filter blockage usually causes power loss and hunting before stalling. A sudden stop with no restart points strongly to an electrical shut-off fault or a sudden air ingress. The absence of smoke tells you fuel is not reaching the combustion chamber in quantity, so do not chase compression first.
2. Outline the checks you would perform in the paddock with only a multimeter, and state the decision point for calling for recovery versus repairing on site.
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Paddock checks, in order:
- Confirm the stop solenoid is energised with the key on. Use the multimeter to check for battery voltage at the solenoid terminal. No voltage means a wiring, fuse, relay, or ignition switch fault, which can often be fixed on site.
- If voltage is present, listen or feel for the solenoid clicking, and check that the plunger retracts. A stuck or failed solenoid is a common sudden-stop cause.
- Crack an injector line and crank to confirm fuel pulses. No pulse at the injector with a good solenoid suggests a pump fault, which is not a paddock repair.
- Check the low-pressure side for restriction: inspect the tank strainer, look for kinked or collapsed hoses, and substitute the spare filter to rule out a bad batch of fuel.
- Check for air by bleeding at the filter and pump; if air keeps returning, find the source rather than repeatedly bleeding.
Decision point: repair on site only if the fault is electrical (fuse, relay, wiring, solenoid) or a simple filter or bleed issue. If the injection pump, injector, or internal engine fault is indicated, stop cranking to protect the starter and battery, and call for recovery. Document the readings so the workshop can continue the diagnosis.