4JG2 Diesel rough idle

[GJBIsuzu]

Hi there, I have a 3.1 diesel Bighorn 4JG2, 1997, 320,000 km. The idle has become very rough and sometimes stalls. OK when motor cold but then as it warms up it gets worse. Often much worse after refilling with fuel and strangely turning the heating knob to full heat on makes it worse sometimes. Under load seems fine but every so often seems to miss just one beat (approx. every 5 mins) Have replaced the fuel filter and all the small vacuum lines but no effect. Have also replaced the alternator. Motor seems pretty good - uses about 1/2 litre of oil every 5000km and not smoking. Any ideas?

[isuzurob]

Have you tried cleaning the electrical plugs to the injector pump? they cause the same issue you discribe or could be an internal fault in injector pump, These are guesses without seeing the truck

[GJBIsuzu]

Thanks will try

[dani4jb1t]

Turning the heating knob to max heat make it worse?? sounds like your engine is swallowing coolant water from somewhere, probably from the head gasket....have you ever checked your coolant level?? also try to see if it bubbles through the radiator filler at idle and when revving it up?? (be careful to open the cap if the engine is already hot)

[GJBIsuzu]

Thanks - I checked the water in the radiator and it is bubbly - guess it is the gasket or the head, damn...

[geeves]

4jg2 engines rarely just blow gaskets on there own unfortuanatly More often its a bad head. If its not too bad there are a couple of products on the market that will delay the inevitable. One is called ironite the other Liquid copper by several brands Also there is a solid block thing that I dont know the name of. Dont consider them a permanent fix but Ive heard of cars that have done 20000km after treatment then sold. Also follow instructions to the letter.
Heads on aliexpress are around 600 The one that went on my wizard 2 years ago was 1600 which is likely the same head. You still need someone to swap the combustion chambers etc

[GJBIsuzu]

Interestingly it turned out not to be the head gasket but a small crack in the radiator and a stuffed pressure cap so that the vehicle appeared not to be using water but had air bubbles in the cooling system (pressure and exhaust gas test confirmed this). Fixing the radiator and replacing the cap fixed the idle but still running a bit rough so I tipped some injector cleaner in the fuel tank and a tank later she is running like new. Will tip another bottle in when I fill her next to be sure...

Thanks for your tips, chances are if I hadn't started looking when I did she would have died for good pretty quickly.