Bad compression......

[RSBUBBA]

Since running a milltek exhaust on my car i had noticed some popping on idle i thought nothing of it.I had my car on the rollers at midland vw and was told there was a fault code for a miss fire on piston 4 so i did the usual new spark plugs,coil pack, and pcv valve.

This hasn't solved the issue.

Today i have just finished a compression test with the following results

cylinders 1-3 were at the 12 bar mark
cylinder 4 9.8!

i had hoped that this was just going to be a bad injector but these results would prove other wise?

The cars booked in next week to investigate further, i spoke to a master tech at Audi who reckons from what i have said it could be, a valve not fully closing/head gasket/piston ring.

im just wondering if any one on here has any ideas?

just to add this is my third 2.0tfsi engine and the other 2 both needed head gaskets doing.

This car has just hit 53k

 

[mty12345]

The popping on idle means my money is on it being a valve.

 

[RSBUBBA]

Is that the exhaust/inlet valve? How could that have become damaged?

 

[Unit9]

Yes inlet valve

 

[mty12345]

Is that the exhaust/inlet valve? How could that have become damaged?

It's hard to say really mate, If the popping was coming from the exhaust then i would take a guess at an exhaust valve. Exhaust valves often burn on the edges, usually due to excessive cylinder temps. One cause of too high a temp would be that the mixture may have been a bit lean in that cylinder at some point.

Inlet valves usually run a lot cooler and it's more likely that, rather than being burnt, that an inlet valve would stick open slighty due to carbon build up.

I'm not an expert on the mk2 engines, but i have heard that they suffer with carbon build up in the inlet manifolds. So that would make sense that it could have built up around the inlet valve too.

 

[Unit9]

whip the inlet manifold off and take alook

 

[RSBUBBA]

Will be looking next week, I will update this when I know more as I've found a few threads regarding miss fires on idle

 

[mty12345]

Will be looking next week, I will update this when I know more as I've found a few threads regarding miss fires on idle

There are plenty of other reasons for misfires on idle, however the fact your compression is so much lower in cylinder 4 means that you need to take the head off and see what has happened. Anything else will just be a waste of your time and money IMO. Only thing that can cause low compression is a valve/ring/piston etc etc

 

[RSBUBBA]

Yes completely agree there! Fingers crossed for next week then. I say fingers crossed im sure it's going to be exspensive regardless!

 

[AlexK1]

You could get them to do a cylinder leakage test, that's what I had to do on mine and turned out to be a broken piston ringland. I had similar issues, high idle misfires and low compression on one cylinder

Sent from my SM-G925F using Tapatalk

 

[RSBUBBA]

Just to clear this, another compression test was done at the dealership and the results were fine! I must have messed it up some how!

Turned out to be injector number 4

 

[Unit9]

Awesome news