TD4 lumpy acceleration / intermittent lack of power

[Guineafowl21]

Hi all,

2002 Td4 Freelander manual, 183,000 miles.

Problem:

Intermittent 'misfire' at 50 mph or so, lack of power up hills, MIL sometimes comes on during episodes, but goes off again. Otherwise, starts and idles perfectly and accelerates very well on flat. No codes.

Already tried:

1. Checked connections to injectors, fuel rail pressure sensor, MAF.

2. Cleaned EGR and blanked off actuator hose.

3. Checked vac accumulator and all hoses.

4. Replaced turbo solenoid and vent filter. Turbo linkage moves a good 20mm during acceleration.

5. Replaced crankcase breather filter (and general service).

6. Replaced LP fuel pump and filter.

Other features of problem:

Lumpiness is noticeable during revving in neutral - mainly 2000-3000 rpm. Also, when the key is in position II and the LP pump is running, I can hear hissing from the HP pump. There are no fuel leaks.

So... If the injectors were causing the problem, wouldn't I have starting issues? Could the hissing near the HP pump be air in the system, or some other fault? Since there are no leaks, could the LP pump be drawing in air through a pinhole, and if so, how do I approach that?

Many thanks in advance,

Andrew