2.5 v6 TDi Quattro vibration under load

[noddyr]

Hi all, just joined the forum and its looks like a great tool for help and to help others!
Recently bought a 2004 2.5 v6 tdi QS, got it cheap with a failed DMF. I'm pretty confident with car repairs and fitted a new DMF with new clutch, all LuK parts. I found that the old DMF was defo no good, it had no movement and looked like the inner part was pusher over to one side. All fitted and ticks over nioce and smooth now, all symptoms have gone.
BUT, when I drive the car there is a vibration when accelerating which feeld like the front wheels are out of balance, its not too bad but is noticable. It seems to be engine speed related, not vehicle speed. Its not a rumble more like a miss-fire or something is out of balance.
I have had new tyres fitted and the wheels all balanced and double checked.
Could this be a MAF problem, or I have heard about engine mounts?
Has anyone had anyting similar happen?
Thanks!

 

[swine]

i needed engine mount replaced but it was more like a clunk when i wasn`t smooth with the clutch. i do know there is an engine mount which stiffens to avoid vibrations when you speed up might be worth checking out. have you had it on vag com. should show up

 

[noddyr]

Thanks for the reply!
Yeah there are no faults on Vag com, and no knocking, when drive is taken up its nice and smooth with regards to the clutch etc.
Ive been doing lots of searching online and reckon it might be the prop, I didn't mark the line up of the bolts when I removed it so its probably in a different position to where it was before, same goes with the front driveshafts but I've read the front ones are not important.
Does anyone agree?
I'm gonna try it in a different position on the weekend, hopefully I will be lucky - I guess it can only physically go in 6 positions, 1 down, 5 to go!!

 

[noddyr]

Hi, I could really do with some help with this one now guys! Scratching my head.
I have now ruled out all positions of the prop bolts, and still this wierd vibration, which I have now noticed is not present first thing in the morning when cold for the first mile or so. But only under load at lower rpms, when I come off the accelerator, the vibration goes away, and idle is still nice and smooth
I have bought a used engine mount on ebay, so gonna try that. Would I be right in thinking thay are the same each side?
I'm also now thinking of checking some of the usual suspects like dirty EGR valve, smooth operation of turbo VGT actuator.
Any other ideas would be greatly appreciated.
Dan.

 

[Magnet]

Hi,

Did you manage to identify the cause of your vibration?

I have a similar issue on my 2001 A6 2.5 v6 TDI Quattro Sport Avant.

I believe I have a duff DMF, I bought the car knowing this, but I have also started to recently notice another type of judder from the engine.

I believe the judder / vibration could be described as a miss-fire.

The vibration can be felt only once I've accelerated through the gears and back off in a gear, once I try to accelerate again in the final gear I then get the vibration / miss-fire.

This only happens under load, and the only way to cure it is to put the car in neutral and let the revs drop to tick over and then rev up engine and pop it in gear, and then all is fine.

I must say I only experience this if the car is driven hard through the gears and then try to cruse. If I pop it down a gear the miss-fire / judder aren’t felt, and if just drive gently… revving up to 3K there’re no issues.

I've been looking over a couple of forums and have seen another driver who has had a similar issue and cured it with a new fuel filter... I've yet to fit mine, if this work I'll let you know.

I have also had a closer look through the oil fill pipe on my engine and have seen the gut retching signs of cam wear on one of the lobes (the finer point of the cam, the rest of the cam lobe area is fine) .

I believe this is the more likely cause of the judder as the play in the cams / vales is likely to feel like a miss-fire when backing off and accelerating again.... though on a side note the car pulls like a train.

What is the age of your A4? It might be worth a look, as I understand some of the v6 engines were fitted with poorly manufactured cams say up to 2000 / 2001 and the long life servicing compound the wear.

If you do check yours just remember to try and move the lobe around to see the wear, unfortunately I didn’t do this when I looked at mine, and thought it was fine. If I had I would have seen the wear and either walked away of knocked another £1k or two off the price… as is going to be expensive to fix.

Rob.

 

[noddyr]

Thanks for your help!
I have changed the fuel filter and no joy, but hey it has to be done at some point anyway! Cams are fine, they are the later type which are different and the problems linked to them are associated with cracking and slipping where the lobes are pressed onto the shaft.
Injectors removed and spray patterns tested, results were very bad and tester was surpised the engine even runs. Rolling road test reveals only 140bhp and 310Nm, somewhat down on power. Boost is fine but airflow is low which confirms the injectors are at fault.
So out they come again this weekend and off to a company called 'deisel Bobs' who have a very good website indeed and will re-con the injectors for £50 a peice, thats new nozzles and re-set the break-off pressures. Hope that cures it!
Has anyone had similar problems to this?
Thanks, Dan.

 

[fjtwelve]

I am getting a bit of vibration as you describe feels like wheels out of balance. Have had the balance and tracking done, not gone away. Injector nozzles being replaced soon, will see if it makes any difference.

 

[noddyr]

Hi and thanks for the reply.
I had new wheels and tyres and that didn't make any difference at all. But I needed them anyway!
Have you had yours on the rollers, like I said mine produced 140bhp, but it still feels pretty gutsy.
Taking my injectors out on Sunday, then send them off and back for the following weekend I hope anyway.
Where are you getting your new nozzles from, and are you getting the rest of the injector set up for break pressures etc?
Dan.

 

[fjtwelve]

Dynoed at 170hp and 387Nm at the moment but we think the turbo is goosed so there's a hybrid turbo going in mext week with the new nozzles and we'll see where that takes us after its been remapped again. Not checking the pop pressures on the injectors yet. Bought Fratelli Boio nozzles from Lear Automotive - Jeremy Lear (lear.automotive@yahoo.co.uk)

 

[noddyr]

Hi,
Just to finish this post off as a resource for others, injectors reconditioned by Deisel Bob at a cost of £300 ish quid and the problem is cured, atlast!
Its worth noting that the service I received from this company was very professional and I was impressed, i can't recommend using them enough!
Now the car has plenty more power and the delivery is nice and smooth, as it should be!

 

[AvantQuattroUK]

I have exactly this issue ... vibration under load. I recently had an issue with my master injector showing a fault. I fitted a used replacement and engine light went off.
As I bought the car faulty and not driven it before I am not sure if vibration was there before so not sure what to do next.
I do have a set of used injectors that came with the master injectors.
Car is also struggling to start apart from when hot.
What would be logical next steps?