Offroad-Express

I've got a frustrating issue that I'm looking for help on.

My 80 series 1-HDT is only on running on 5 cylinders at idle. It runs fine on 6 when revved. Number 3 is the cylinder that is lazy at idle.

It's had the pump rebuilt about 15 months ago and has just had new injectors put in which have since been pulled out and retested (by reputable diesel specialists) and all are working fine. It's had the valve clearances checked and they're out of spec with only two within spec. Number 3 the lazy cylinder is 0.06 (they should be 0.15 from factory and up to 0.1).

Compression is okay with most cylinders around 400 with worst number 6 at 375 (25 max variance).

The engine has done around 470,000. It's about to get an intercooler and gturbo.

So what next? I know the valve clearances close up over time but I would have thought any clearance would still mean it would idle - even 0.06.

Only other thing I can think of is something gone wrong with the pump.

well, if it aint the injector its the pump inn'it? may be turn the fuel up a little see if the miss at idle disappears, if it does you should be all good for turbo, but if it is still missing then no use turbo'ing t till the problem is found, didn't damage the no3 injector line when mucking around in engine bay?

Yeah, what he said.

If the compression is good, it rules out mechanical issues with rings, rods, bores, valves etc.

First check I would be doing is to crack the No.3 injector line at the injector at idle and look for fuel pulse/presence. Got fuel, suspect the injector burst pressure at 1st stage . Sounds like the second stage is all good because it runs on 6 as you bring the rev's up. If you see no fuel, start to suspect the pump, but try next step first to be sure...

Swap No.3 injector with another injector and see if your miss moves cylinders. If the miss remains at No. 3, you have ruled out the injector being the problem. If the miss moves, you do have a crook injector. Its a bit like playing with plug leads on a petrol to find the miss, except you just crack the injector lines at the injectors one at a time. Sounds like you know that though

If nothing changes, next place to look at is the pump. Not much you can do yourself there, other than pull the No.3 line off and look for dirt.

Hey had similar problem, found that had a bent delivery spring on number 5 on pump. Not very common but my diesel pump guy said in 15 years only seen one spring break

Like diesel boy said, swap a pair of injectors around and see if the fault moves with the injector or stays on three. If it moves it's the injector,if not it's the pump.