2009 3.0tdi lumpy idle.
 

I am looking for some help tacking down the problem with my A8.

At idle the car appears to be on 4 or 5 cylinders, and when engaging drive or reverse causes a lurching effect which is most disconcerting.

It began only when cold, and I changed the glow-plugs initially, to no avail. Since then it has now developed to happen almost constantly when the car is idling. It has been on VCDS and had a coolant temp sensor changed (think it would have faulted when I disconnected to check glow-plug circuit was operating).

The car drives perfectly from 1000rpm upwards, is still economical, and has no visible smoke (DPF may be masking this). It does seem to "smell" very rich in the garage when started and idling, but that's not scientific, it never normally gets started and idle for any time inside .

Anyone any ideas, or suggestions of garages with diagnostic experience in central Scotland. It's been on VCDS , but I don't believe they will have spent time on injector measuring blocks etc, although if injectors were at fault, would they not generate fault codes?

I have searched online to look for similar issues, and ruled out glowplugs, coolant sensor, and the air distribution system is clean from looking at the throttle body unit upstream of the inlet manifold Y-piece.

Any suggestions or help welcomed.

Cheers,

Iain.

Faulty injectors don't give codes in my experience, even when running with one completely unplugged. I had similar problems, in May, I was able to stop the engine and unplug an injector and then drive and observe any change, then reconnect and try another until I narrowed it down.

It is important that you stop the engine before disconnecting an injector's electrical connector as if you unplug it while open, it will stay open as they require reverse current to close them.

I think one of mine was lazy, as if it was stuck open, it would have stayed open even with the electrical plug off.

If you unplug 5 and each one makes it worse and another makes no difference, they it must be that injector/cylinder.

Someone on here had something similar - bad compression in one cyclinder due to some valvegear problem IIRC.

In vcds can you go into the injector readings , look at the injection quantity deviation mg/str .......milligrams/ per stroke , big plus readings is the ecm trying to get that cylinder to contribute, to keep the engine in its smooth running adaptations

As a test if you have big plus readings on one injector swap that to another cylinder to see if the fault follows it .

But big plus readings are not nessasarly injector faults .....they can be other cylinder issues .....compression ...valves and so on

Like Snap says do not unplug Piezo injectors whilst its running .

You could do a ohms check across the injector pins think it will be about 150 ohms , also do each individual pin to injector body ......should be open circuit .
If you get any resistance that is a Piezo crystal breech to ground =duff injector .

Would be god to get a compression test done also to rule out any losses

Lee

Thanks, I'll do the injector testing tonight that I can do without vcds. Should have bought VCDS years ago, but been lucky enough to have access to it any time I needed until now.

Cheers, Iain

Did the checks on injectors, all 6 show similar resistance, 190k ohms.No shorts to body on any and running with each disconnected makes little difference.
Spending some time under the bonnet, in the vee is a vacuum operated diaphragm which is cycling whilst it idles....can anyone tell me if that's normal.

Also followed all vacuum lines I could see , but no sign of any splits or leaks....

Any suggestions welcomed. I will get the injectors checked on vcds also.

Sounds like the egr vaccum acctuator I think your on about , should it cycle ?? Mmmmm not sure on that ..... I would say no , would of thought it would have a fixed duty cycle at start up .... I could be wrong though .... I digress .....

Just as a test .... un plug the vac pipe off the egr pod and put a bolt in it plug it up , the egr will not work now but for testing purposes at this stage it's ok .

When you switch ignition on or start it up do both the swirl flap motors do a sweep , are plastic rods from the swirl motors connected to the linkage on the inlet manifolds , you normally get codes for swirl flap issues but check any way .

If I remember correctly when at idle the swirl butterfly's will be closed , one side swirl the arm is down , the other side the arm is up .

What I'm thinking here where you say he car seems to run on 4 or 5 cylinders
I'm wondering if one swirl is open and one is closed giving a miss match in air flow per bank giving the missing cylinders feel to the engine , albeit you would think you would lose 3 cyls at a time but some thoughts anyhow

Still carry out the injector tests for the mg/str per injector it may hold a clue , the ohms tests can all be ok but injectors could still have issues , if the injector corrections all show one bank to be on the plus side this is a tell tale to a 'per bank ' issue .

With diag it's a case of ....carry out appropriate tests .... rule out .....move on to next test .....assuming makes a fool of me and you , or the fit parts till the customer runs out of money approach , I see this near enough everyday .....part fitting on the back of code tests .....no follow up testing to prove or dis prove whatever codes are present

Yadder yadder I'm rambling on here aren't I ......... ' computer says noooooo '

Just looking at pictures of 3L tdi engine , does yours have vaccum operated egr or is it the electric one , if it's the electric one the vaccum acctuator you say is cycling could be the egr cooler switch over valve .

Mine has a vacuum egr, that is what is cycling . Not sure it's related, but will blank and try.
Need to get a vcds on it again to check the injector flowrates.
Thanks for all the suggestions.
Any suggestions for quality diagnostics in central Scotland?

Cheers, Iain.

Is this like your engine

http://i618.photobucket.com/albums/t...pst3hovokm.jpg

Is the unit you can see cycling to the left of the green box ??

Hi, thanks for all the thoughts.
It was the diaphragm in the red box that is cycling but disconnecting the vac hose from it makes no difference.
It may be cycling due to the uneven idle?
The hunt goes on....

Do you mean diss connecting the egr it carrys on cycling ,or diss connecting it the engine is still missfireing

When I had my misfire, the rod to the left of the green box would thrash back and forth at idle - it was random, not in a rythm, I put is down to explosions in the exhaust manifold.

With the vacuum hose disconnected from the egr diaphragm, the uneven idle remains. The diaphragm stops cycling.
In answer to the earlier question, the swirl flap rods appear to be acting normally.

Any other suggestions welcomed. :Confused:

The rod to the left side of green box is egr cooler switch over valve , when engines cold egr cooler is bypassed , when engine gets warm egr gasses go through cooler to reduce cylinder charge temp when egr is in use .

The air mass volume plays a big part in how much egr duty is deployed , so for instance if swirls are having funny spells , air mass volume can change and this will affect egr control duty .

Possibly aswell snap D where you say the linkage was flapping about randomly it could of been back pressure from manifold or it could of been ecm turning egr control and cooler bypass off randomly due to misfire detection , very often in missfireing situations some of the emission control will be turned off .....its part of limp strategy .
That's why I was asking op to check the swirl arms , it's hard really to give diag advice over a forum ....your relying on the poster to give as much info back as possible but without the car in front of you it's difficult .

Could still be injectors this one but with diesel missfires I like to rule out egr and swirls , I like the diag posts ......as you have probably noticed hehe brain testers

Arrr right you are ..... more diag needed on the injectors mg /str .... do you use supermarket fuel or branded stuff by the way

I tend to buy fuel from wherever I'm near, not brand loyal, and it'll get supermarket fuel occassion, but not solely. Too long in petrochemical site to get hung up on fuel "quality".
The swirl flaps do seem to be behaving as described above as normal.
VCDS to check injector flows is next.

Car booked in to Argyll Diesels on Friday...I'll update the post after the car has been if they have any success tracking the fault. Fingers crossed!

Yes keep us informed of the findings +++

It appears my car is suffering from an exhaust valve sticking open slightly leading to low compression at idle and hence the lumpy idle!

2009 car, Audi approved used in 2011 at 41k miles, now on 69k miles, serviced every 8-9k and driven in a moderate fashion, ie allowed to warm up, but given enough throttle on occasion to keep the dpf clear and exercise the turbo.

Disappointed to say the least!

However, it's only metal.

So I now need to know if anyone has undertaken a cylinder head removal with the engine in the car, and if there is a workshop manual in circulation that I can buy or download?

Any help greatly appreciated.

Iain

Sorry...Just found manual in Tech Dump.....brain a bit out of sorts!

Mmmm couple of things come to mind

1 If its exhaust valve sticking due to carbon deposits up the stem of the valve this could be treated chemically , you need someone with a BG flushing machine or similar .
You use chemical to treat the inlet system via a 'fogging nozzle ' which inturn will clean the combustion area and on the valve overlap period it will be able to work at the valve stems ...... definatly worth a go , they rattle like a good un running on the stuff but it can work wonders for carbon cleaning

If its a burnt valve ......yes head off only will fix that .

2 Is this engine on hydraulic followers or hydraulic buckets .... Burnybubbles will know about this
If it is on hydraulic followers the relief valve in the bucket/follower can gum up and stick closed so it cannot reliieve its self and in some cases it lift the valve off its seat causing loss of compression .

With this fault get two of the Forte hydraulic additive chemicals , do an oil and filter change first and put the additives in with the new oil .......had great results with this stuff especially with hydraulic issues where you get the clack clack noise from them .

Couldn't agree more, we stock the full range of Forte products and have had surprising results with them. If it is a hydraulic follower then use there engine flush for an extended period, drain the oil and leave the engine to cool. Then refill with fresh oil, oil filter and Forte top end treatment. It make take a few miles for a result but it's definitely worth a try before removing the head.
I've used this method on a lot of VAG cars and cured a lot of valve train problems. Good luck+++

Thanks for the suggestions.
I don't think its a hydraulic issue, as the follower is clearly free of the camshaft when the valve should be in the closed position , as seen by the other exhaust valve. No discernible valve train noise difference from bank to bank, or cylinder to cylinder when the trusty screwdriver to ear is applied.

So that leaves us with possible a carbon build up on the stem , as I think it closes once the revs come up and the cylinder compression rises quicker than the leaking valve can relieve it. SO chemical cleaning may be an option.

What is the BG machine mentioned ? Is it something I can do at home, or can anyone suggest someone in central Scotland who is known and trusted? I'm a bit sceptical of these things normally, but I am prepared to try something.

I cannot see it being a bent valve, as that would require some contact or hydraulic issue, neither of which there is any evidence of.

Have a look at this demonstration with Frank Massey .

Where abouts are you in Scotland? will find out from my Top Techs garage forum who is closest to you .

https://www.youtube.com/watch?v=w4ABTo42tKA

There's no buckets but the followers are solid with a hole in them for the oil gallery into the head, the rocker is also a roller rocker so it considerably helps cam wear :)

One thing to bear in mind just in case, is the cams can not be reinstalled without the correct tooling, you need a special locking set that hold the cam sprocket as it has a backlash compensation ring, and then you put them onto a jig and fit another tool that holds both cams at tdc ready to be dropped into the head, I dare say with a bit of common sense and some imagination you could make up some stuff to fit them but the VAG tools to do it are around £500 iirc and why I opted for a replacement head instead of repearing my own.

You can physically measure injector return flow and total fuel return flow at idle. You will need tolerances from the workshop manual or Bentley. Im sure you can find something on google. Tbh with you find unless you have the kit its probably more cost efficient to fine a BOSCH diesel specialist, most garages will farm out stuff like this to guys who spend all day doing injector type diagnosis. Just find a decent one.

Sorry for silence on this, I have been away for a week or so, car has been with Audi for assessment of fault....

I'll report the outcome ASAP.

Okay, so Audi UK were hopeless on phone when asked for "someone technical" to speak to about what may have caused the issue with my car.

Hamilton Audi however were much more interested, and took car in for diagnosis, confirmed a low compression in one cylinder, and my car is now repaired. The report suggests an inlet seat has become "misaligned", although I believe this should say exhaust ... unless the valves are so close together that the exhaust valve was fouled by the inlet..however I was unable to view the parts, and didn't want to push the matter in the circumstances.

It has had a new cylinder head fitted, with associated gaskets etc and fluids replaced. Suffice to say Audi made an exceptionally generous contribution to the repair.
I am mightily surprised and delighted , despite knowing the car is impeccably maintained and completely genuine, it is over 6 yrs old, with only partial Audi history (albeit having 7 recorded services in 69000 miles, and being sold to me as Approved Used with non Audi stamps in book at 2 yrs old) . I had no prior experience of Audi Hamilton, (new branch) but will certainly endeavour to put some business that way in the future.
I am still disappointed that the fault developed, and am undecided whether the car will remain the "keeper" I had in mind for it, but fingers crossed it is at least back to good health and will be used daily for a month or so to ensure it is in fact fully cured.

Thanks to all who offered suggestions and support.
I do have an intermittent parking sensor fault to address now....anyone got phantom black front outer sensor lying about..??

Cheers, Iain.

Wow ! thats a good result to get warranty on the age of the car , valve has become miss aligned ......mmmm not so sure how that happens , apart form it getting a clonk off a piston .
Good news its all sorted out anyhow .

Ouch, glad you got it fixed and even better to get a large portion contribution.