Idle erratic on 1996 Bighorn 4jg2 diesel

[stephanv]

Hi All,

Great forum to find.... this is my first time on one of these, so I hope I have the protocol right.

I have a 1996 4jg2 Bighorn with an all electronic injector pump. It is "hunting" at idle, but not always - it used to do it once or twice a year for a few seconds - now it does it every time I drive it.

It seems to be hard getting diagnostic diagrams/information because from what I can tell most of the 4jg2's are not fully electronic. I have pulled error codes from flash dtc and have error 34 and 31.

It does it hot and cold, and seems to happen when the load changes (put in park/drive, switch on aircon, move the steering wheel while stationary). It is like the computer is having a tug of war with a sensor.

Any ideas very welcome - I am at my wit's end.

[geeves]

Someone posted diagnostic codes a while ago Might be worth searching for. When was the fuel filter last changed

[stephanv]

Thanks for the quick reply

I've searched the diagnostic codes. As far as I can determine (although I could only find 1998 codes for a 3.0 litre engine, not the 4JG2) they are EGR and MAP sensor faults.

I've replaced the vacuum lines (some were loose) and had the egr valves on the bench - they work OK, as well as trying it with the egr vacuum disconnected so the valves stay shut - all makes no difference.

Fuel filter has always been done every 20K and oil and filter every 5K. Last fuel filter was about 10K ago.

Could a faulty MAP sensor be the cause of the symptom? Also, anyone have any suggestions for someone to take it to in Wellington - Holden in Porirua said their scan tool wouldn't read it because it is Japanese. Another garage suggested I had a battery problem, which makes no sense at all given the symptoms.

[walruz]

Ooopps, had same problem 'hunting' at idle 1996 EFI pump.The error codes were retrieved but must of been written in some language that NO-ONE understood! Sooooo after much head scratching the pump was reconditioned and bench tested and has run fine since. Should add that was in Auckland 5 years and 120,000 km's ago! Truck has been in Aus last 4.5 years and still runs strong (touch wood). Very few Bighorns in Aus as they are only allowed as previously owned personal imports. Anyways good luck, in my experience the hardest part is finding a 'competent' technician familiar with ISUZU.

Cheers

Walruz

[geeves]

Go to Diesel Doctor in Nelson st Petone. He can sound a little vague on the phone but knows his stuff. When he resealed my 2.8 pump he charged 1/4 of the next lowest quote.

[stephanv]

Thanks for the input - went to see the diesel doctor - 99% sure it's the pump. saving for a recon job. Cheers s

[jayceenz]

I've now blown two of these engines in less than a year, and both of them were hunting/surging at idle. The agents here now inform me that the surging is caused by a worn governor etc in the EFI pump system. When under high load such a steep hill the computer sends the incorrect fuel metering messages to the system and it will either under fuel or over fuel. The result is the same...one wrecked block. Their advice is to have the system and injectors thoroughly checked and the pump overhauled immediately, or face the consequences. Julian

[geeves]

Interesting Ive heard similar stories about small Nissans. Underfueling will only cause lack of power but overfueling or injecting at the wrong time will send exhaust temps through the roof with inevitable results

[jayceenz]

Hi there Jeeves, Quite right mate. According to some reconditioners here ( Christchurch ) there are blown motors all over the country due to fauly EFI systems. Some will not do you a recon without they get the pump to have overhauled at same time. They also inform me the earlier blocks with iron liners not the chrome ( '96 on ) will give more tolerance over a high flash heat range. However I've done that on my second motor and it still siezed with no warning at all. Hmmm might have to start another thread eh.

[geeves]

All Isuzu diesels had chrome liners and a rebuild useing factory isuzu parts will be chrome as well. The iron liners are after market and less than 1/4 the price. They have only been available a few years so dont know how well they last (dont think theres many rebuilds with more than 100000 on them yet) but knocking 4000 off the cost of a rebuild in a vehicle that will be worth not a huge amount more than that afterwards makes a lot of sense. Its also very hard to get the rings to bed in right when you use chrome liners resulting in high blow by.
All of this makes me think keeping my rattly old 89 bighorn another few years sound a good idea

[geeves]

When they fail what do you find on the insde. ie cracked block scored liners or something else. Im thinking about a few other 4jg2 engines that have met sudden unexpected failures.