4JX1 2003

[teak8]

G'Day
Have an intermittant fault in that when idling motor revs will hunt up to approx 200 RPM seems to be heat related .When temperature builds under bonnet no foot on throttle revs vary from approx 800 to 1100.
Any help please.
teak8

[geeves]

Possible very bad news.
Do you have confirmation that the injector recall was performed on this engine?
Check the oil level Also check it has not been contaminated by diesel.
The injectors on this engine have oil on one side and diesel on the other. When the O ring fails diesel gets into the oil. The lucky drivers have the engine seize on them (10000 repair)
the unlucky drivers have the engine go into runaway. This is not nice when driving down the highway and you know theres a traffic jam in a few kms but the car just goes faster and there is very little you can do about it.

[walruz]

Check out ITOC UK. Lots and lots of information there also trained Isuzu mechanics offering advice.

[teak8]

G'Day According to my information recalls applied up to Eng. No. 600 000 my engine No.950 000

[geeves]

I would still check the oil for diesel. Other possibilities on this engine are one of the many sensors. Really there is very little a home mechanic can do with this engine

[teak8]

Car has been through recall personally checked sump level & OK Don't understand why check engine light not on

[roscoe]

Gday Teak, The 4JX1 has a positive crankcase ventilation system which is common for a lot of engines, The vent hose from the crankcase goes straight to the intake pipe between the air cleaner and the turbo. In the cases where the engines were over running to destruction, so much diesel had leaked into the sump the normal oil fumes had become volotile to the point the engine could run on them alone via the crankcase vent hose. If you suspect that the overrunning is being caused by diesel contamination in the oil then simply disconnect this hose and run the engine, if it still does it then its an electronic glitch. Obviosly the oil level would be higher than normal if there has been contamination.

At the end of the throttle cable there is a sensor which tells the computer the position of the throttle pedal at any given time. This may be worth checking. There is also a sensitivity adjustment on this sensor which is a pig to get at.

When I had starting problems with mine, it was either hard to start or it would stop within a few seconds after starting, from memory there was some variation of idle speed but anyway, the problem was oil contamination in the injector harness and after I replaced it, no more problems plus the engine check light never came on at any time during this.

Hope this is been helpfull
cheers
Roscoe

[teak8]

Thanks Roscoe at the moment the car is with a" Guru" who has actually been Japan with Isuzu to do a training course he beleives it could be the Rail Oil Pressure Sensor & according to him the check engine light does'nt always come on .Willgo along with him & see how we go .What is your opinion of these motors?
Thanks again

[roscoe]

Hi again Teak, The engine check light will only activate for something that is monitered by a sensor so if the computor dousnt know about it then it wont trigger the light.
There is another way that the check light can come on with no fault codes and this has cropped up with other brands of vehicles too. The check light circuits are very suseptible for some reason to stray EMF emmisions, (electro magnetic fields) . The main culprit here is unshielded wiring and the most commen is after market electrical equipment that has been added to the vehicle such as security alarms etc.

As for my opinion on this engine, I did my trade as a Diesel Mech before electronics came into being so ive always prefered the fully mechanical systems but trucks are getting well over a million kms without any electronic glitches so the systems now are well sorted.
The 4JX1 is very unique in that, A, It uses Unit injectors which no other Jap engine of any size or make uses. Unit injectors have only ever been used by Catepillar, Cummins and Detroit /MTU ( general motors) and they have always used mechanical means to pump the injector ie, an extra lobe on the cam shaft and rocker arm or direct overhead cam, and, B, The 4JX1 uses high pressure engine oil to do this so its a rare beast indeed. The scary bit is that its so totally reliant on the computor to manage all this, however mine has done 185,000 kms and apart from the injector harness getting contaminated with oil and the recall done, it runs very well and im impressed with how smooth it is and how well it drives.
( I just wish that synthetic oil was a bit cheaper)


Roscoe

[teak8]

Thanks again Roscoe am still learning & what you say gives me encouragement.