2012 1.8 tfsi special ed - low compression on cylinders 2 & 3. Help needed!

[Shortxiv]

Hello,

Newbie here and looking for some advice for my father in law's 1.8 tfsi A3 special edition s-tronic. It's done just over 60k and is well looked after. He was driving it a few weeks ago and it suddenly started misfiring and threw up the engine management light. He took it to a garage and they couldn't determine the issue but tested the obvious stuff like the spark plugs. He opted to take it to a dealership, who stripped the head and said very little other than the valve seals not being perfect and that cylinder 2 & 3 have low compression. They're advising he need an engine replacement. 

This seems a bit drastic, what do you guys think?

 Here's a link to the video provided by the Audi dealer

https://youtu.be/1gt5vYmaj2U

Any input or advice would be massively appreciated

Thanks!

Darren

[cliffcoggin]

I agree with the diagnosis provided by Audi which is very clear: the low compression is a result of worn or broken piston rings, possibly also associated with worn bores. (The soot on the valve stems was caused by incomplete combustion of the fuel as a result of the low compression.) Three solutions occur to me:

[1] Rebore and totally rebuild the existing engine.

[2] Buy a new engine.

[3] Buy a secondhand engine.

Options 1 will give you effectively the same as option 2 in terms of performance and durability if it is done properly, i.e. a new engine. Reboring used to be cheaper years ago but that may not be the case now given the high cost of labour. Option 3 will be cheapest but the quality will be a lottery.

[Magnet]

Hello Darren,

Lower compression on two adjacent cylinders is text book head gasket failure between those two cylinders, unless - by rare coincidence, these are the only two cylinders to suffer from poorly seating valves and/or piston/ bore wear.

I haven’t looked at the video, so excuse me if I’ve missed something, but incase I haven’t, I would make the following suggestions:-

Ask them to show you the removed head gasket, and carefully examine the remaining gasket between cyls. 2 and 3. 

Valve seals? Do they mean valve seats. If so, - not perfect? Well you wouldn’t expect them to be on an eight year old car! 

Have they measured the bore wear? If so, ask for the figures. 

Did they carry out a secondary compression test (obviously before dismantling) whereby a small quantity of oil is added to the offending cylinders to give a better indication of whether the low compression was due to bore wear or valve issues, or indeed simply a head gasket. 

Personally, I would not be thinking along a different engine until you have understandable answers to some of the questions. 

Perhaps you could keep us informed. 

Kind regards, 

Gareth.

[cliffcoggin]

Gareth.

Watch the video. I think you will change your mind.

[Trevor]

can honestly say I have not seen carbon build up within the engine like that for a very long time!

[Magnet]

Point taken Cliff, but link doesn’t work on my system.

So are we are talking carbon build-up here?

If so, my take on it can still hold, where the head gasket has blown twixt 2 and 3, resulting in unburnt diesel being pushed ( at twice a petrol engine compression) over into the adjacent cylinders. 

If this car was mine, I would still be asking the same questions.

Kind regards,

Gareth. 

[cliffcoggin]

The video shows a short engine (i.e. head removed,) that had had liquid poured into all four cylinders. Two pots still had liquid inside; the other two were empty. That to me is unequivocal proof that the bores and/or rings are worn.

[Magnet]

Many thanks Cliff - clearer now. 

If it were mine:- 

Back to my some of my original questions. Have the bored been measured to assess the degree of wear? Is this were tolerable? If so, would new rings be sufficient or does it need new pistons? Cost of pistons? 

Back to initial concerns:- why would two adjacent cylinders/pistons (only) wear? Strongly opposing combustion pressures from blown head gasket? 

I wonder if Darren’s father in law has owned this car for some time and so knows of any history of previous issues. Perhaps he has had it from new, and knows it’s been trouble free..? 

Kind regards,

Gareth. 

 

[Magnet]

Please excuse the typos in the above. Seems the window to ‘Edit’ has changed, and it now has a fairly short time span.

Wondered if it has indeed changed Trevor, or am I missing something? 

Kind regards,

Gareth. 

[cliffcoggin]

I guess we'll never know the outcome as Darren has not had the courtesy to reply, or even acknowledge our responses.