I've had my 07 GV for a couple of weeks now and have been sorting out a few little things on it, mainly cosmetic, but the last week I've noticed a strange mis fire/knocking noise when cold. If I start it, first time every time, it rattles and knocks until I've revved it over a couple of thou rpm. It's fine after that. Almost like I have to blow out the cobwebs every time I cold start. Any ideas on what it could be. It has 118k with full history and cam belt at 90k.
Any thoughts gratefully received.

 

If you have determined this is "combustion knocking" and not bearings being starved of oil, 1st. thing I'd do is clean the injectors. Mechanics do this the easy way by pouring some Forte' in the fuel filter, then leave it running awhile. I've seen Forte' for sale at £12 per tin. It's totally useless pouring a cleaner in the tank, it never works. Might do though if you use a super-cleaning diesel over months.
This motor BTW uses solenoid injectors not piezo -- this is a good thing. Piezo injectors cost around £600 EACH, and they DO go wrong like in the VW Golf GTi., developing a short from piezo-stack to ground. This is the 400volt drive area.

Of course, if the knocking is a bearing def., I'd remove the oil and filter, and flush out with flushing oil, partic. if the existing engine oil is thick, black and has gone semi-solid. Then hope no damage has been done. Be sure it's not a ticking tappet you're hearing, which gets pumped up by the engine oil pump after a few seconds.

Plenty to check there.

Leedsman.

 

As leadsman says Injectors needing a good clean out and should be a necessity for everyone's diesel engines in a service, but lets just leave it at that.
I have my suspicions on the tappet side however where there is possibly a build up of sludge in the tappets. But as said a good flush out should clear it hopefully.
Keep us posted on this one as I think I have heard of this before long time ago.
Come to think about it, VW's have an issue like this due to using the wrong type of oil.

 

check the glowplugs, it will still start even if they have all failed, but sounds like a bag of spanners

Regards
Richard

 

That's how I'd describe the noise Richard. After normal pulling away it stops after maybe 200 yds as the revs increase. I've got a few things to check now. Thanx for everyone's input.