My Father is having problems with his 2005 Fabia 1.2 HTP 3 cylinder 20K miles. The car is having a misfire in cylinder 1, it happens randomly and he has tried to debug it with a VAG-COM and gets an error that there is a problem with cylinder 1. He has tried changing the coils on all plugs, he has also changed the Lambda Filter and the temperature sensor as he was recommended to. None of the above have fixed the issue, he then tried a compression test and Cyl 1 was 10 and cyl 2 & 3 were 15 so this seems to be the problem. He put oil in to the cylinder to try and break down the carbon and the pressure went back up to 12 -> 13 the car runs fine for a week or so but has now started to miss fire again. The pressure in Cyl 1 has dropped to 11 again. Does anyone know what the cause of this could be, someone though it could be the head or value and would cost €1500 to fix. The thing we cannot understand is if it is mechanical is why it is so random and is not miss firing all of the time.

Does anyone have any ideas?

Thanks.

The loss of compression on No. 1 cylinder could be down to a crack or flaw in the casting of the head, or a leak in the gasket or a damaged or poorly seating valve. Some years ago I had a Peugeot 405 which developed a misfire, a compression test showed one cylinder was down. When I stripped the head I found an exhaust valve with a crack in it. You could also lose compression through a damaged cylinder or piston rings, but you tend to see blue smoke in the exhaust. I would imagine you will have to remove the head to find the fault. good luck.

If the pressure increases after you have put oil down the bore, it is an indication of a problem with the piston rings and/or piston. With a poorly seated valve the oil would not make any difference to the compression pressure.

With piston ring problems, as the engine turns over faster there is less time in which to lose the pressure, but you will get the gasses blowing by the rings and pressurising the crank case. Is there an oil mist from the engine with the oil filler cap removed?

I agree with the above, however sticking valves are fairly common on the three cyinder engine. If the exhaust valve was sticking this would mean fuel is still injected but not being burnt fully. This can lead to a drop in compression due to bore washing.

I had low compression on one pot turned out to be a gasket blown between two pots.

Maybe a broken valve spring, altho this would not improve with a bit of oil.

What is the condition of the spark plug ??

Have you had a leakdown test done? I know when I was losing compo on one cylinder we pressurised the cylinder and listened through the adjacent spark plug hole to check for hissing. Highlighted a slight gap in the head gasket between the 2 cylinders.

Thanks for all the replies, they have also changed the spark plugs so they should be OK, I will take a look and see if they are wet / dirty again. I will also check the exhaust to see if there is blue smoke. Will also try the test for leakage in to the other cylinder.

As it appears to be mechanical would you not expect to see the problem all the time, right now it can be days before it reoccurs.

Looks like the head needs to come off anyway!

He left the car in to Skoda yesterday (as he could not get the tools to do the job himself). Turns out the head needs to be replaced and the timing chain etc... There was a problem with the value seat / exhaust valve.

As the car has under 20,000 Km Skoda said they would pay 70% of the cost, however the total cost is now €2800 (£2200) which seems very expensive the original quote was €800, Also this seems to be a bit of an issue with the 3 Cyl 1.2 as some other Skoda garages said they had 2-3 in a day with the same problem. Does anyone know if Skoda have acknowledged this or are they just dealing with the issue if people complain?

I have had the same thing with 1.2 polos. got a feeling myself its a fueling issue.

Hi, Fabia Dublin it looks like you will have to pay 30% of the 2800 euros (840 euros) for your Skoda dealer to fix the fault. the car is 2005 so is it now over three years old & out of warranty? because at 20K that's a low mileage for the year. I know it's a pain to pay out for a replacment head, but if you took it to an independant to repair the head / replace the valve I would imagine the cost could be similar with no real guarentee of future problems. Has the dealer indicated what might have caused the problem?