2004 A4 Cabriolet

[Jd1959]

Hi, I am new to this site and Ive have my A4 cabriolet since March however i have a problem with what I would call Pinking ! .  In the old days I would have just retarded the ignition timing/distributor but now all of these issues are usually controlled by the ECU as far a im aware.   The pinking is happening when going up through the gearbox or when accelerating at higher speeds.  if i were to dip the clutch while driving the pinking would stop.   No EM light on dash . Any ideas what is causing this problem as it is getting really annoying. This is my first Audi , I love the car but im very close to getting rid if I cant get this problem solved .  I have had some work already carried out on the secondary air pump and pipes etc.

[Dan3222]

My gut says the timing belt is out by one tooth! Assuming it does have a belt and not a chain. If not it will most likely be fuel related so change the fuel filter and run a good quality injector, double dose it on first use. See if that can make a difference.

[Jd1959]

That's a good point Dan the timing belt may be out if there is one.  I will have a look at the fuel filter and get some injector cleaner.  I have already tried using a higher grade fuel but that did not work.   I'll let you know how it goes. thank you for the advice

[Steve Q]

Welcome to the forum John :) 

youll find the members a friendly bunch and I'm glad Dan could help with your question :)

cheers

steve

[Jd1959]

Ok so far , The car i still at the garage , they said  if the timing belt was off by one tooth then the pinking would have been there all of the time ( which it hasnt) .  They have put a computer on it to check the mixture etc,  they say there are 2 knock sensors not working which can cause the problem and the injection thermostat shows up as a fault . The garage is going to replace these one at at time to see if the fault is resolved to save me money.  garage will ring me tomorrow to update.

[Dan3222]

Fingers crossed!

[Jd1959]

Update !   After spending about £800 on mainly labour and replacing the 2 knock sensors, the injection thermostat, secondary airflow pump and sensor and pipes, the Pinking is still there but worse.  The parts that were replaced were shown as fault codes so no more engine management light . The pinking starts evening at cold temperature only when driving , does not happen when revving .  The garage check the compression and it is low ish on 2 ports but surely this cant be causing the pinking .   This is my first Audi and so far as much as I like the Audi when it was working, this fault is kind of putting me off getting another and I may need to sell it.  

[Magnet]

Hello John,

Sorry to hear about your continued problem. The garage's reference to slightly low compression on two cylinders is of interest. 

Have they told you which two cylinders show this slightly low compression? If not, would you be able to find out from them, since if this is on two adjacent cylinders then your problem could be explained by a faulty head gasket blowing between the two cylinders, and introducing opposing compression across to the neighbouring piston.

Would you be able to let us know?

Kind regards,

Gareth.

 

[Jd1959]

I will let you know I have the details on the job sheet at home and the compression results are on the sheet .

[Jd1959]

Hi Gareth  . Cylinder 1 = 110 psi   Cylinder 2 = 90 psi  Cylinder 3 = 120psi and Cylinder 4 = 150psi

The garage have done a test to see if it is the gasket but they believe it is not the gasket but the Valves

 

John

 

[Trevor]

Hi John

Gareth is right in his diagnosis about the head gasket but I would strongly recommend they carry out a Cylinder Leakage Test (using compressed air through a gauge hooked up to the cylinder (where the spark plug) to introduce air into the cylinder). The idea is that when you introduce compressed air into the cylinder, if it is head gasket blowing between cylinders then you will lose pressure, if it is wear in the bores/rings then the air will escape into the crankcase and you will hear it through the oil filler cap, if it is escaping through the valves then the air will either come out of the exhaust or inlet manifold, if head gasket through the coolant then you will get bubbles in the coolant tank. Simple test and non-evasive.

If they don't have one of these bits of kit or don't know how to use it then take is somewhere that does, you'll save yourself a fortune on wasted labour & parts.

Compression may also be down due to quality of oil...e.g. washdown due to excessive fuel or weak spark. If the oil smells of fuel then it is washed down and needs replacing urgently.

[Jd1959]

Hi Trevor the garage has carried out a leakage test I believe, they are a well equiped service centre.  I suppose if the gasket was replace and cylinder head reconditioned then surely the fault must be solved as there appears nothing else that can be causing it.   The pinking has got gradually worse everytime a faulty part has been replaced .  When I first got the car the heater was not working very well somI had the heater matrix replaced and it worked fine. I was told by the person who i bought the care from  that the engine management light comes on and his garage told him it was the secondary air intake sensor, so I had it checked from the fault codes but it turned out to be the secondary air pump and a leaking pipe. Then the pinking started . but the EM light came on again and it was the injection thermostat and another secondary air part , pinking got worse again to the point that it pinks from a cold engine whereas it used to be from just a hot engine..      Any body want to buty an A4 ?  lol

[Trevor]

I would also have a good look at the spark plugs because these will show up whether the cylinders are running lean or rich and also which ones are likely to have experience detonation.

[Jd1959]

Hi Guys , update!  at the begining of last week I decided to let the garage take the head off and investigate from there, and Gareth was right the cylinder head gasket was blown in 2 places between the ports.  So the cylinder head has been sent to be tested and skimmed and has arrived back at the garage today where it will be refitted with new gaskets etc.  I might get it back tomorrow or Friday  and after trying it, if all is ok I will get the gearbox fixed or replaced as the syncromesh has gone in second gear.  So fingers crossed.  Thanks Gareth, Dan and Trevor for all of your input and advice .

[Magnet]

Hello John,

Glad the cause has been established, and I take no comfort from the fact that my diagnosis ( via. the question of which two cylinders were lower) turned out to be correct.

Now, your sophisticated diagnostics is fine, but being from the old school of mechanic-ing as the great Fred Dibnah used to say, I tend to look at symptoms and ask questions and take a logical approach to these things. Those compression figures just jump out at them, and irrespective of knock sensors etc.etc. it just shouts head gasket blowing between the two adjacent cylinders and passing opposing pressure onto the neighbouring cylinder - which says 'this isn't right - I going to let you know by pinking" . Thimple, as our friends on hind legs would say! 

Machanic-ing with logic should over rule the diagnostics, and the garage's failure to spot this problem from the outset, has done serious damage to that which sits in your back pocket! Great shame. 

Still John, the beloved car is going to be well again and that is important.

Back to those compression figures - I shudder at their interpretation of valve problems. Oh dear dear me!  I ask, is there still a need for the elderly here or should we (elderly) all be sitting in homes out of the way? I've probably got shoes older than these chaps, and I guess I should now have forgotten most of what no one taught me in the first place!  Jovial rank over.

Good luck with it John,

Kind regards, Gareth.