300tdi Auto, knocking noise on idle.

I've had a look through a number of post of a similar subject but not really answered the question, so was hoping someone out there might have an idea.

300tdi auto, 1997, makes a real knocking noise on tick over, but stops about 900rpm and there is a distinct reduction in the noise if you select any gear.
Drives really well, changes gear no problem, maybe holds the gears a little longer than normal but not too bad.

Its really difficult to know exactly where the noise is coming from, even with the noise it ticks over perfectly and revs freely throughout the range.

I've only just bought it as it is really clean, no rust and its to replace a very rusty but mechanically sound 200tdi manual I have, so if all else fails I'll swap the engine and box, but thought I might try and sort out tis problem if its viable?

Thanks in advance.

If " Its really difficult to know exactly where the noise is coming from" it's a difficult one that. engine or gearbox?

its worth checking all torque convertor bolts

vac pump?

I think it's gearbox, or more likely the flywheel/torq converter. Because its centre of the box and engine it's difficult to say for sure.

The noise is like big end knock but as mentioned disappears completely at 900rpm, no vibration, and no loss of any power.

Mine sounds horrible and similar symptoms to yours but I've shown it to a few people who know the 300tdi and they said "they all sound like that"!

The direct injection makes em noisy and then so does a Worn vac pump etc in other words it might not be a problem at all

Mind you the 200tdo is supposed to be worse still

there not normally that noisy ,they often have a diesel knock at idle due to h/d clutch or poor kit fitted , vac pump or poor rocker /follower etc are obvious not normal running faults as is a loose t/c bolt or drive plate breaking up

Hi,

I can record mine and put it up here if you want to hear it, its a 300TDI Auto 1998. No knocking noise just usual old Diesel sound.

Chris

check the crank shaft pulley bolt hasn't worked loose as well as I've seen several clanking 200tdi's

This is no normal diesel knock, its like someone hammering on the chassis. depending on the depth of the snow here tomorrow, I'm going to get underneath and have a good look and listen. strange thing is that the knocking doesn't increase in speed with the engine revs and as soon as you get to about 900-1000 rpm it stops.
Has anyone had any issues with collapsed engine mounts, wondering if that might be the culprit, the other strange thing that has started to happen is the difflock light comes on if you drive it hard, its not actually putting it into difflock but enough movement to move the lever for the light to come on, a slight touch on the lever and the light goes off!
it's this and the fact that there's no increase in speed of knock with the revs and the engine and box run so smoothly?

I'd check all mounts. Plus exhaust. If lock light is coming on then there might be something pressing against gearbox as tho it has moved round. Just a thought.

Thanks for all the advice, I'll start with the easy, engine/gearbox mounts, then front pulley (had this on one of my 200tdi disco's) think too noisy for vac pump but will look and the very last resort, box off and torque converter.
I'll let you know how I get on tomorrow.

jamesmartin said:

its worth checking all torque convertor bolts

Click to expand...

Checked out all but this suggestion, have you had experience of this before James?

as said check exhaust, mine bangs on startup.

Just thought I'd put an update to the above problem.
After many hours of trawling the internet, checking various suggestions I finally found someone with the exact same noise and symptoms.
A phone call to Dave @ Ashcrofts to confirm and hey presto "Broken Flexplate"
Box seperated, flexplate ordered and hope to fit before Christmas.

Thank you for all your help, hope by posting this message others will find a slightly quicker resolution.

Many thanks