Burning plug in cylinder 2

[AScoff]

I’ve had this issue for a while now

the car has been back and forth to the garage, who I’m now sacking off 

 

started with a valve/intake clean to resolve a carbon build issue 

the car ran for a week, really well, then threw an injector!

4 new injectors, a set of plugs later 

 

this then started the back and forth!

seems the inlet manifold gasket

wasnt changed and it looks like there was an air leak causing overfilling (I’m guessing) which caused the plug to foul, then burn

the plug when removed, smelt of petrol!

 

pressures across all 4 cylinders were spot on and in balance

 

if i put a new plug in, it will run fine but when I’m coasting, or at a slow, steady speed, it will happen again!

 

I’m on injector set 2

swirl flap mech was changed this last time, new injectors, manifold gasket, and plugs!

 

im going to try and sort this myself this time as I’m not letting the original garage

anywhere near, and I’ve not got the cash to start again with a new garage!

 

was going to strip the inlet manifold and work from there

 

any pointers / suggestions most welcome!!

 

pics / bad plug and normal for comparison!

[pikpilot]

14 hours ago, AScoff said:

it looks like there was an air leak causing overfilling (I’m guessing) which caused the plug to foul

 

Are you sure it is just fuel on the plug. The photos suggest oil as well.

[AScoff]

Not 100% sure no! - I'll give it a wipe

 

So, if its oil but the balance of pressure is the same across all cylinders - what is my starting point?

If its oil, why has the plug been seemingly burnt away?

 

I'm trying to make sense of something my garage has failed to do in months.. without just changing stuff for the sake of it, like they have done before!

 

[Warrior193]

Possibly worn valve stem seals/guides?

[AScoff]

I'm hoping this is the issue, and not rings... 😏

[xman]

What engine is it? Iirc the 1.8tsi engine in gen1 and gen2 versions are notorious oil burners due to broken or blocked oil control rings.

 

I'm thinking it could be caused by debris in the combustion chamber, possibly due to the cleaning you had. That would explain why the tip is missing/damaged. The iridium alloy tip is super hard, and you'd not burn it away. If so then the cylinder wall, piston crown and head likely damaged too.

 

The only sure way to tell for sure is would be to remove the head . Alternatively you could use a borescope to take a peek inside and examine the damage.

 

 

 

Edited 13 February by xman

[AScoff]

Thanks - its the 2.0 Tsi CCZA Engine

But, I agree, it does look like the last plug - Mechanical damage! 😞

[AScoff]

I've compresion tested Cylinder 2 vs 1

 

2 is 9.5bar

1 is 8 bar

 

this seems to me to be quite a difference!

But, not what I was expecting?

 

If I've got worn/failed cylinder rings, I'd expect a lower compression in the faulting cylinder?