CriticalCommonEngine

Isuzu Bighorn: 4JX1 high-pressure oil system and injection pump wear — long cranking and no start

4JX1 high-pressure oil system and injection pump wear — long cranking and no start is a common engine fault on the Isuzu Bighorn on the 1998–2002 cars, and we rate it critical. Putting it right costs $1,200 to $4,500 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: 4JX1
Years: 1998–2002
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 4JX1 is unusual: rather than a conventional injection pump feeding the injectors with fuel pressure, it uses engine oil at very high pressure to fire them, through a pump and an oil rail pressure sensor. That makes it fussy about oil condition in a way ordinary diesels are not, and the pump is a known wear item — Isuzu's own service records show pump replacement was a routine workshop job. As it wears, the engine takes longer and longer to start, particularly cold, until one morning it does not. Poor fuel and neglected oil changes both bring it on sooner.

What you would notice

Cranks for several seconds before firing, worse when cold or after standing
Starts, runs for a moment and dies
Lumpy idle that smooths out once it has been running a while
Owner routinely parks facing downhill or leaves it on a battery charger

How to check it

Where to look. High-pressure oil pump and oil rail pressure sensor on the engine; symptoms show at the key

Insist on a genuinely cold start — arrange to see the car first thing, and if the bonnet is warm when you arrive, come back another day, because a seller who has warmed it up before you got there has hidden exactly the symptom you came to check. Count how long it cranks before it fires: a healthy one catches quickly, and several seconds of churning is the warning. Start it again after it has sat for twenty minutes and see whether the second start is worse. Check the oil condition and the service history closely, because on this engine the oil is part of the injection system and skipped changes do real damage. Ask what oil grade is used and how often it is changed. If a workshop inspection is possible: have the oil rail pressure sensor and high-pressure pump output checked by a diesel specialist familiar with the 4JX1 specifically.

Parts involved: High-pressure fuel pump.

What it costs to put right

$1,200 to $4,500 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

“How long does it take to start from cold on a winter morning?”
“Has the high-pressure pump or the oil rail pressure sensor been replaced?”
“What oil goes in it and how often?”
“Has it ever failed to start and needed a tow?”

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 the sources below. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them.

EngineCode.uk — Isuzu 4JX1 specifications and common failure modes
JustAnswer Australia — Isuzu/Holden Jackaroo, Wizard and Trooper 4JX1 engine problems
Fixya — Isuzu Trooper (Bighorn) 4JX1 common rail starting faults

Isuzu Bighorn buyer questions

Is 4jx1 high-pressure oil system and injection pump wear — long cranking and no start serious on a Isuzu Bighorn?

We rate it critical and common on the Isuzu Bighorn. The 4JX1 is unusual: rather than a conventional injection pump feeding the injectors with fuel pressure, it uses engine oil at very high pressure to fire them, through a pump and an oil rail pressure sensor. That makes it fussy about oil condition in a way ordinary diesels are not, and the pump is a known wear item — Isuzu's own service records show pump replacement was a routine workshop job. As it wears, the engine takes longer and longer to start, particularly cold, until one morning it does not. Poor fuel and neglected oil changes both bring it on sooner.

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

$1,200 to $4,500 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 1998–2002 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.