Mitsubishi Triton: 4D56 Injector Seat O-Ring External Fuel Leak

The 4D56 diesel injectors use rubber o-ring seals at the injector seat that degrade with age and heat cycling, allowing diesel fuel to seep externally around the injector body. The leak is visible as a black oily film around the injector tops and can worsen until fuel contacts hot engine components. A well-documented fault on high-mileage ML/MN examples, particularly those used in hot climates or with extended service intervals.

• Diesel smell inside cab or under bonnet
• Black oily film around injector bodies on the rocker cover
• Smoke from engine bay if fuel contacts exhaust manifold

1. 1

   With engine warm, remove engine cover and inspect each injector body with a torch and clean rag.

2. 2

   Look for wet or oily residue around injector bases.

3. 3

   Check for fuel smell.

4. 4

   Inspect rocker cover area for staining that indicates long-term weeping.

Parts involved: Fuel injector.

$300 to $700 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has any injector work or seal replacement been carried out?”
• “Have you noticed a diesel smell in the cab or engine bay?”
• “When were the injectors last serviced or flow-tested?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.