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Isuzu Bighorn: 4JG2 Diesel Injection Pump Oil Seal Failure

4JG2 Diesel Injection Pump Oil Seal Failure is a common engine fault on the Isuzu Bighorn on the 1991–2002 cars, and we rate it major. Putting it right costs $500 to $1,200 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 12 documented faults on the Isuzu Bighorn.

Vehicle
Isuzu Bighorn
Engine
4JG2
Years
1991–2002
Fuel
diesel
System
Engine

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

All Isuzu Bighorn faults12 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the High-pressure fuel pump yet. We would rather show none than show a picture of a different part.

What goes wrong

The 3.1-litre 4JG2 turbo diesel in the UBS69 Bighorn develops oil seal failure at the injection pump shaft. Hardened seals allow engine oil to seep from the pump body or, in worse cases, enter the fuel system. This fault is long-documented across the 4JG2 engine in both Isuzu Trooper and Bighorn applications in NZ and Australia. Age and heat cycling harden the pump seals; high mileage or vehicles that have not been run regularly are most susceptible. Repair requires injection pump removal for reseal or rebuild.

What you would notice

  • Oil weeping from injection pump body or rear shaft seal area
  • Oil contamination visible on the pump housing and adjacent components
  • Engine oil consumption without apparent external engine oil leak
  • Diesel smoke or oil smell from engine bay after startup

How to check it

Where to look. Diesel injection pump, front-right area of engine block

  1. Inspect the injection pump housing and shaft area for oil wetness.

  2. Clean the pump and surrounding area thoroughly, start and idle the engine for a few minutes, then recheck for fresh oil seepage.

  3. Check engine oil level and condition.

  4. On higher-mileage examples, ask directly about injection pump seal history.

Parts involved: High-pressure fuel pump.

What it costs to put right

$500 to $1,200 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 injection pump been resealed or rebuilt?”
  • “Any oil weeping noticed around the injection pump area?”
  • “When was the engine oil last changed and how often is it checked?”

Now check the Isuzu Bighorn 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.

Isuzu Bighorn buyer questions

Is 4jg2 diesel injection pump oil seal failure serious on a Isuzu Bighorn?

We rate it major and common on the Isuzu Bighorn. The 3.1-litre 4JG2 turbo diesel in the UBS69 Bighorn develops oil seal failure at the injection pump shaft. Hardened seals allow engine oil to seep from the pump body or, in worse cases, enter the fuel system. This fault is long-documented across the 4JG2 engine in both Isuzu Trooper and Bighorn applications in NZ and Australia. Age and heat cycling harden the pump seals; high mileage or vehicles that have not been run regularly are most susceptible. Repair requires injection pump removal for reseal or rebuild.

How much does it cost to fix on a Isuzu Bighorn?

$500 to $1,200 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 Isuzu Bighorn years are affected?

Our research records this fault on the 1991–2002 Isuzu Bighorn. 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?

Inspect the injection pump housing and shaft area for oil wetness. Clean the pump and surrounding area thoroughly, start and idle the engine for a few minutes, then recheck for fresh oil seepage. Check engine oil level and condition. On higher-mileage examples, ask directly about injection pump seal history. Look here: Diesel injection pump, front-right area of engine block