Rough / odd idle behaviour with old 1HZ motor

[sunrk]

1hz motor in my 80 has a really rough/odd idle behaviour where it feels like one injector randomly doesn't fire at random intervals. The injector pump and injectors were replaced about 6 yrs ago. Never been touched since. I could replace injectors with a full set of brand new ones myself but I'm not sure I'd want to have a good at replacing the injector pump.

The 1HZ is the original motor to my 3/92 80 and it's currently up to almost 639 k km's on the odometer.

I'm trying to save for a replacement motor (angling at 1hdft) but at present just need to keep the old donk humming. It doesn't have a turbo kit and wouldn't support one due to it's age and level of wear.

 

[roscoFJ73]

Does it start up easily and smoothly? Does the engine temp make a difference? Do you get a puff of white/grey smoke when it misfires?

I would pull the injectors out and have them bench tested. New nozzles, if it needs them, will be cheaper than buying new injectors. If the spray pattern is ok ,it may be the injector springs are weak.
The pump is simple enough to get off in theory. In reality they can sometimes require enormous patience and effort to break the pump away from the flange. You need a high quality puller that hasn't done umpteen dozen 1HZ pumps in its previous life.

 

[sunrk]

It normally starts up fine though sometimes I need to crank longer than I'd think necessary (like 5+ seconds). The engine oil pressure comes up without a problem (though that's probably not relevant).

The issue does seem to be less noticable when the engine is fully hot but it doesn't go away. I have not noticed any puffs of white/grey smoke. I check it regularly for white smoke as that's a telltale of cracked head or failing headgasket allowing coolant into one (or more) of the combustion chambers. Doesn't mean there isn't a head crack though and I think the head is original. I don't notice any significant loss/usage of coolant though I don't check that very regularly.

I'll try to find a decent diesel shop to talk about injectors. The set that's in now were reconditioned ones along with the injector pump. Fitted at the same time. The rough idle didn't become obvious until I replaced the old engine mounts with brand new genuine ones a bit under a year ago.