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Mitsubishi Delica: 4M40 injector return pipe O-ring seal failure

4M40 injector return pipe O-ring seal failure is a common engine fault on the Mitsubishi Delica on the 1994–2007 cars, and we rate it major. Putting it right costs $180 to $450 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 18 documented faults on the Mitsubishi Delica.

Vehicle
Mitsubishi Delica
Engine
4M40
Years
1994–2007
Fuel
diesel
System
Engine

This page covers the Mitsubishi Delica as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mitsubishi Delica faults18 documented faults on this model

What you are looking at

A single common-rail diesel fuel injector photographed against a plain background.Example of the part — not this vehicle

A common-rail diesel injector. Contamination damages the nozzle at the tip.

Panoha · CC BY-SA 3.0 · Wikimedia Commons

What goes wrong

The rubber O-ring seals on the injector return fuel pipes of the 4M40 2.8 diesel deteriorate with heat cycling and age. Failed seals allow diesel fuel to weep back along the return rail and contaminate the engine bay or mix with engine oil on high-mileage examples. The problem is endemic to the 4M40 engine family and is a routine finding on pre-purchase inspections of L400 Delicas over 150,000 km.

What you would notice

  • Diesel or oil smell from engine bay with no visible external leak
  • Oily residue or fuel staining visible around injector return pipe connections
  • Rough idle or slight fuel-related misfire as return pressure drops

How to check it

Where to look. Top of the 4M40 engine along the injector return fuel rail, at each injector banjo fitting

  1. Check the valve cover area beneath the return rail for diesel residue.

  2. Run the engine to operating temperature and re-inspect for fresh seepage.

  3. If a workshop inspection is possible: Remove the engine cover and inspect each injector return pipe O-ring seat for fuel staining, oil discolouration, or visible weeping.

Parts involved: Fuel injector.

What it costs to put right

$180 to $450 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.

Ask the seller

  • “Has the injector return pipe O-ring kit been replaced, and if so when?”
  • “Is there any fuel smell noticed during or after driving?”
  • “Has the engine cover been removed for inspection?”

Now check the Mitsubishi Delica you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

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.

Mitsubishi Delica buyer questions

Is 4m40 injector return pipe o-ring seal failure serious on a Mitsubishi Delica?

We rate it major and common on the Mitsubishi Delica. The rubber O-ring seals on the injector return fuel pipes of the 4M40 2.8 diesel deteriorate with heat cycling and age. Failed seals allow diesel fuel to weep back along the return rail and contaminate the engine bay or mix with engine oil on high-mileage examples. The problem is endemic to the 4M40 engine family and is a routine finding on pre-purchase inspections of L400 Delicas over 150,000 km.

How much does it cost to fix on a Mitsubishi Delica?

$180 to $450 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mitsubishi Delica years are affected?

Our research records this fault on the 1994–2007 Mitsubishi Delica. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Check the valve cover area beneath the return rail for diesel residue. Run the engine to operating temperature and re-inspect for fresh seepage. If a workshop inspection is possible: Remove the engine cover and inspect each injector return pipe O-ring seat for fuel staining, oil discolouration, or visible weeping. Look here: Top of the 4M40 engine along the injector return fuel rail, at each injector banjo fitting