Question about 1998 Isuzu Trooper

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Isuzu Trooper (Bighorn) 4JX1 Engine Common rail injection. Year of manufacture1999 We have problem with this vehicle. Refused to start for about one year. Parked in workshop that period. Sent my guys to see it (in a town about 400 K's away. Shop there had replaced second hand H.P. pump, New injectors and new glow plugs. Still failed to get it to run. My guys got it running. It was driven to us and I rode it around for about seven days to make sure everything was ok.. Parked it on a slope one day and it began to misfire on start up. Idled but would not pick up RPM. Bled the sysytem, and it started up behaved as it should. The next few days it became progresively worse....Went to start it two days later....Zero....just cranks....We've tried to clean the ORPS with WD still nothing... This engine is unknown to the agents here in Zambia, who don't have a program for it....Likewise for any replacement parts required.... The system has been bled and shows no signs of air. Anyone got any idea's? Pretty please?....Its driving us a little bit crazy Regard Jongee10

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  • Hi Kennedy if you can get it towed to Kitwe, that's where you'll find us. If you have to tow it please remove both propeller shafts first. If you don't you'll damage the gear box.
    0968449905 or 0974178929
    Best Regards
    Don't forget to rate the answer

  • Benjamin Manda
    Benjamin Manda Dec 17, 2016

    Hi,ican solve your wizard problems just call me on 0977802754 Benjamin



4 Answers

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Try fitting a seperate transfer pump between the tank and HP pump(quick/cheap fix only) and see if this resolves the problem. If yes check filler cap(no air lock), air leaks in supply hoses or transfer pump(and of course the usual "check the fuel filter").
If not, dig deeper:

Isuzu Trooper (Bighorn) 4JX1 Engine Common rail - 72f3b1a.jpg
J-1-15(not indicated) : Earths glow plug relay to enable glow plug circuit.
ECM : Electronic control module
IS : Idle switch
ECT : Engine coolant temp
OTS : Oil temp sensor
IAT : Intake air temp
FTS : Fuel temp sensor
INJ : Injectors 1 through 4
RPS : Rail pressure sensor
EGR : EGR vacuum pressure
MAP : Inlet manifold pressure
APS : Accellerator position sensor

Posted on Oct 30, 2010

Testimonial: "Many thanks Suzman, Hope you won't mind if we need to pump you for more knowledge.... Very very very helpful.... Regards Johngee10"

  • 6 more comments 
  • Blaauwbokse Jan 22, 2011

    i have a similar problem but my 1998 3.0 diesel looks like it gets no petrol, sometimes it gets no power at al and I can give fullgass but no differance, what can this be?
    thanks for hopefully helping me out.
    Cheers Ron, Hastings New Zealand.

  • Hi Ron,
    Seems you may have a similar problem on your machine to the one we've had....The 4JX1 has taught us a lot we didn't know before, but specificly for this particular engine.

    First I'll advise you check the obvious things...Make sure that your battery is charged fully. I'll explain why later.

    Next make sure that there's no air in the fuel system....On the filter housing you'll see a ten millimeter bolt, which should be loosened and once loose push the plunger atop the housing to remove any air....If bubbles come out you'll know that that was the problem or part of it.

    With this particular engine the ORPS (sensor) gives the type of problems you're talking about.
    The sensor in question is fitted inside the tappit cover into the oil rail (which is the cylindrical pipe fitted over the valve assembly....It has two sensors, one being the ORPS and the other being an oil temprature sensor. To get to these it'll mean removing the tappit cover which means first removing the inter cooler....then the oil feed pipe which fits into the side of the cover, Remove all the screws (five each side and three at each end)....The ORPS is the smaller of the sensors....It is a sensor which operates with a cystal....The oil preesure pressing against it will cause a very small voltage which is actually a pulsed signal....That signal is sent to the management computer and controls the solid state switch which allows the circuit for the injectors to beecome active....Remeber the battery? If the battery is not able to turn the engine at what you'll hear as a normal speed the oil pressure will not be enough to send the signal which opens the injectors....The ORPS (Oil Rail Pressure Sensor) cost's about two hundred and twenty US$ and if you do the job yourself your probably save a similar amount on labour charges....The engine oil is also critical....Only use the recommended oil....If that has not been used....Buy double the amount of the correct oil and two of each filter....Drain what's there and then refill with the recommended oil (once vehicle is up and running) run the engine for thirty minutes or so (pref on the road) and then re drain and again fit the other set of filters and refil....We don't like the chemical engine flush addatives, too dangerous, esspecially in a diesel engine....

    Hope this is help Ron Let me know how you get on. you can send your reply to this same web site...I'm one of the experts....

    Cheers for now....

    Best regards


  • Ps Why dodn't you become a member? Just suggesting....

    Regards Johngee10

  • itsalis33 Feb 02, 2011

    i sell secondhand engines from experience change the engine and replace with a 4jg2
    with a manual diesel injector.4jxi has alot of complication and no mechanics to repair.

  • We do and have....Find out how they work....They were designed and made by mankind, they can be fixed by us too....

  • emaxtrd894
    emaxtrd894 Nov 07, 2012

    i want buy 4jx1 proformance chips !

  • Anonymous Dec 20, 2016

    Ferdinand wants more answers to this question
    , what is your cars symptoms??
    never piggy back others, it invites gross mixing of facts, and issues.
    try starting your own post, no really.
    year of car
    country it's in (be like the 5th ever....)
    engine type. 4JX1

    The 4JX1 is a 3.0 L direct injection diesel engine, turbo, some intercooled, which replaced the 4JG2 in the Isuzu Bighorn/Trooper/Holden Jackaroo. It uses unit injectors and 4 valves per cylinder.
    the post all symptoms.
    and miles
    and what was done or not.
    what tests done.
    and if you scanned the PCM. (no year no joy)

    the wiki lists this engine as PROBLEMATIC.
    and was sold up to 2005 in some countries.
    no county no joy
    try to learn,:
    that not all cars are the same.
    nor even and engine (same name), in all countries\and for SURE by year, SOME are electronic controlled
    some are as old as 1998, not like 2005 at all.
    so what car do you have in what country and year.

  • Anonymous Dec 21, 2016

    engine, and if turbo diesel.
    and full symptoms and tests done.
    otherwise its a silly guessing game.


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I see this old post and im having same problem. But how come in Zambia - Nigeria and such like places you always resolve a problem here in the UK we rely on main dealers to much.
Also wondering if you ever fixed your troopers await a reply
Welsh Warrior

Posted on Apr 20, 2014

Testimonial: "Hi Welsh Warrior, Yes we sorted out that vehicle and several of that type after that one. The answer to your question is simple. In Africa we don't have access to all you have in Wales or wherever, so, necessity being the mother of invention, we're forced to fix things as replacement is usually very expensive. If you're intending to work on your vehicle, or if you'd like to advise your workshop guy's, the following are the areas of interest. 1) crank shaft sensor, 2) camshaft sensor, 3) oil rail pressure sensor (ORPS) and $) the oil rail temperature sensor (ORTS). Problems with these engines are usually caused by using the incorrect engine oil. Use of the specified oil is critical as is a shortened service interval. Also keep in mind that if the injectors have been removed, without marking when removed, or replaced, the injectors will need initialization, meaning re-coding with the engine management system. that particular operation is carried out with the use of a scan tool."

  • 4 more comments 
  • Welsh Warrior
    Welsh Warrior Apr 21, 2014

    Put oil in mine today and got it started but it feels lumpy like its missing any idea's Guys Welsh Warrior

  • Hi Welsh Warrior, Let us know what work has been carried out to the vehicle and the problems you're facing. The more info you can give us the more likely we'll be able to help you. If for example you've removed and replaced the injectors or reinstalled the same injectors, but in different positions, they will need (re) initialization. The more info you give us the better bach. By the way I was born in Bangor. Regards John

  • Welsh Warrior
    Welsh Warrior Apr 23, 2014

    Changed tank initially found its leaking oil from broken sump nut.

  • Welsh Warrior
    Welsh Warrior Apr 23, 2014

    Had a lot of air in the fuel system. Injectors got changed on a recall 3 years ago and it feels the same but starts easier. The engine check light is very intermitant and its very smokey but had been stood for 2 plus years.

  • Benjamin Manda
    Benjamin Manda Dec 17, 2016

    also the clean diesel is very cardinal to this engine(low Sulphur diesel

  • Marowa Ob
    Marowa Ob Apr 17, 2019

    Hie I am specialialist in 4jx1 engine call 0785199604 Harare Zimbabwe


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Check Rail oil temperature sensor, it is next to pressure sensor.
It is a thermistor which send signal to ECM from very cold to hot.
If the resistance is high, it is cold, when motor runs, resistance is lover with the temperature and ECM change fuel mixture. Check the wires first for change in voltage, should go lover when warming up. Either way to low, or to high temperature signal and the engine won't run properly. You go to garage it seems no one has any knowledge about that. I had this problem in Australia and "the professionals" asking thousands of dollars to fix it, with no warranty. I paid $12 for extra wire. They couldn't tell why is this problem occur.
Try other sensors as well.
Good luck

Posted on May 09, 2013

  • RichW
    RichW Jun 27, 2014

    Was the oil pressure down as this continued to occur? Common problem is wear in the pickup sump o-ring. Mine was very slightly able to be wriggled. Used some gasket cement (Ultra Blue) after cleaning up all joint areas. made sure no sealant able to enter the inside of the pickup pipes (There are 2 pickups - one short one long so do both). When reassembled the engine started first turn but died again. Oil pressure rock steady slightly over 6 MPa. Tested with Tech2 and rail pressure is too high so will replace the ORPS common rail pressure sensor (under the valve cover). This should give me a steady idle which is the main indicator of this problem. It just loses power steadily after running OK for a period of time. The ORPS is intermittently faulty on mine. It will start and run as steady as a rock for an hour (idling). Next start after a few days and same old dying fault. Will replace the ORPS!!!!


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I have the same problem with mine too. Its been down since November 2009. Im in Mongu and if you find someone who can fix it let me know. Mine is a Wizard with 4JX1 engine


Posted on Feb 24, 2011

Testimonial: "Hi Kennedy, If you can get the vehicle trucked to Kitwe, I'm confident we can have you drive it back. Regards John"

  • 3 more comments 
  • Hi Kennedy, We can't travel to Mongu, but if you can manage to get the vehicle loaded onto a truck and get it to us in Kitwe, we've learned a fair amount about this engine type to be able to help 0968 449905.
    Regards Johngee10

  • markteggla Mar 23, 2011

    I have the problem with the diesel fuel in the radiator. I have begun to strip the top end off to get to the seals. Please can I get some advise on how to pull the injector sleeves. I've made a crude tool to pull but without success.
    Do they just pull straight up or do they screw in.
    Thanks in Advance

  • c j w Feb 04, 2013

    I modified a slide hammer and the sleeves came up with about four light taps each five min work,and they were leaking water into cyl.

  • Davison Apr 12, 2016

    am in Zimbabwe if u gt a problem with 4jx1 get hold of me 00263712777040

  • Anonymous Dec 19, 2016

    3 years late. but great!
    seems that they don't scan the PCM
    and use gauges and meters to find causes?
    guessing is expensive, sure.

    diagnose using the correct tools.
    seems you work on complex trucks lacking a factory service manual. ?
    this book covers all the tests.


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1 Answer

How to fix an injector pump of 4jx1 engine

this is a USA forum what country are you in?
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the word fix has many meanings
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The 4JX1 is a 3.0 L direct injection diesel engine, turbo, some intercooled, which replaced the 4JG2 in the Isuzu Bighorn/Trooper/Holden Jackaroo.
It uses unit injectors and 4 valves per cylinder.

European and Asian buyers could opt for the diesel.

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We live in New Zealand and own a 1998 Isuzu Bighorn, 3.0D. About 3 months ago it started idling roughly and stalling just after starting. Then it stalled on me when I was driving 70kph. It also has no

wow first post ever posting country ,what a brave person. !!!!
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The 4JX1 is a 3.0L direct injection diesel engine, turbo, some intercooled, which replaced the 4JG2 in the Isuzu Bighorn/Trooper/Holden Jackaroo. It uses unit injectors and 4 valves per cylinder.

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