Low compression on my FSI....what to do?

StefanoP

Member
Dear all,

I was wondering how come that the flap of my FSI was repeatedly blocked due to oil vapours and finally I asked my mechanics to check the compression ratio of the cylinders. As was probably obvious, the compression on this 90.000 miles engine is very low in all cylinders, (from 5,4:1 to 7,8:1...:eek:) proving that this little car was abused by previous owners so much that even its engine's innards are worn out. :mad: Rebuilding the engine is out of the question because of the high costs, Audi would not provide a 'light' engine if not for a huge pile of money and I'm wondering what to do now. The FSI drives well with the ProBoost modification kindly supplied by Steve but I'm somewhat missing the FSI sophistication. OTOH buying an engine in a scrapyard (there is one for sale around £450 in Italy) is sort of a lottery. I'd buy a complete car (this could give me more parts that I could need) but one can't find much under £1500 in Italy and of course you'd have to be sure that the FSI engine is better than mine. Any ideas? Thanks!

Stefano
 
The compression may be down due to sticking or carboned up valves - long shot but possible. You could try some engine top end cleaner for injectors valves and piston rings, may improve may not. Are you running only on premium 98+ unleaded fuel, if not that certainly will contribute to the issue. Can you repeat the compression test after putting a small amount of oil down the spark plug hole to see if the compression improves?


Once Covid restrictions are over it may be worth buying a complete car from further away and either collecting it on a trailer or having it shipped to you.
 
Just my penneth worth, buying a used engine is like buying am unknown used car except worse, an ok risk for trade as labour is free to them and potential mistake but if you're paying for the install costs they tend to tot up very quickly on-top of the price of an engine. Always worth a question, why was the car so bad the engine is now for sale? You could get lucky with a genuine engine from a trusted member who's cherished car has been written off from the rear but that would be looking for a needle in a hay stack. In my experience, bone yards, scrap merchants and parts sellers on the usual sites don't like to give out true mileages or service history making it a lottery.

Imo getting a rebuild on the block with valves and seats re-cut, assuming the guides are good, and lapped in will give you an almost as new engine for not a huge amount more than doing it the other way except this way you're guaranteed success.
 
Just my penneth worth, buying a used engine is like buying am unknown used car except worse, an ok risk for trade as labour is free to them and potential mistake but if you're paying for the install costs they tend to tot up very quickly on-top of the price of an engine. Always worth a question, why was the car so bad the engine is now for sale? You could get lucky with a genuine engine from a trusted member who's cherished car has been written off from the rear but that would be looking for a needle in a hay stack. In my experience, bone yards, scrap merchants and parts sellers on the usual sites don't like to give out true mileages or service history making it a lottery.

Imo getting a rebuild on the block with valves and seats re-cut, assuming the guides are good, and lapped in will give you an almost as new engine for not a huge amount more than doing it the other way except this way you're guaranteed success.

Hello VdT,

you are obviously right, my idea was, as I wrote in my message, akin to a lottery. The fact is that rebuilding the engine would cost no less than £3000 at least and this is not economically viable. My bad luck that after 2 A2s I bought for little money in almost perfect shape, the FSI had been badly abused and the engine has some issues, the most important being the low compression, i.e. badly scored bores or something like that. It drives well, after the fitting of the ProBoost mod kindly supplied by Steve, but you can't help thinking that something is still missing. As a first step I've resumed my search for 98-100 RON petrol, so difficult to find here, and I filled her tank (it was near empty) Monday with ENI 98 gas and a injector cleaner. I'll put some miles on it and see what happens in terms of performance....sadly compression will not improve. The strange thing is that oil consumption appears to be negligible, but then I've not used FW888WS too much during the last months.

Cheers

Stefano
 
Low compression is not necessarily due to worn/scored bores. Put a small amount of engine oil into the combustion chambers and repeat the compression test. If it makes no difference, the cause is unlikely to be the bores and more likely to be a blown head gasket and/or burnt valves. The latter shouldn't cost you £3000 to repair.

RAB
 
Hi @RAB I already asked for a second compression test with oil. And like you now waiting the results. Low grade fuel probably a contributing factor also.
 
I may be over thinking this but maybe with the oil drop test maybe worth thinking about how to introduce the oil into the cylinder. Remember the BAD piston head has a hollow (some benefit to fuel delivery) and it would be pointless if the small drop of oil pooled there and not round the rim of the piston head.

Just a thought.

Andy
 
If the problem is caused by fuel, that points towards the valves being the culprits. Turning the engine over will put the oil where it needs to go.

RAB
 
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