andyfreelandy said:

Trying to quieten the TD4 - 2002 135k miles.

Couple of questions, I am assuming it is injector 'knock' and have tried controlled experiments on different fuels.

Took sound level readings at same place in cabin at 1,000 RPM and then used 300 miles of supermarket, then again with 300 miles of usual BP, then 300 miles of octane boost diesel.

Thought I'd found the difference but there was no correlation after trying to repeat the experiment several times. With a phone app sound meter held (not touching) just above the steering wheel with the car held at 1,000 rpm I sometimes get 55dB and sometimes get 71dB - I can hear the difference and it appears 'random'.

Can I pull off injector plugs while engine is running without knackering the electronics??

Yes
Try using a long screwdriver as a stethoscope - surprisingly effective.
If so I could maybe eliminate it - any other ideas? Bottom pulley replaced and it seems a 'top end' noise.
Ideas please !?!?!? Thanks

Noisy lifters? Has the car been well serviced in the past? What oil have you got in there and when was it last changed? What about something on the serpentine belt or, hopefully not, the timing chain?

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andyfreelandy said:

Thanks, regular 10-40 oil changes and breather and turbo filters.
How do you diagnose lifter noise?
Will report back on isolating the injectors.

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