Persistent misfire (help!)

[Pigchem]

Hi All - I've always found it dead useful using forums over the various years of VW and Audi ownership to troubleshoot issues but I might finally have reached a point when I need to make my own post!

I've owned a 2.0L 4-cyl 16-DOHC FSI, 54 reg for about a year now, got it on the cheap understanding that it would have issues - most of them have been fixable, but typically the difficult issue cropped up just before its MOT back in Jan.

Currently the car has a cylinder 1 misfire (P0301) code and an EGR performance problem (P0404) code. It did have a P0597 - thermostat faulty - code, this was a straightforward replace the thermostat valve situation and the code was cleared.

EGR valve issues in the past have been sorted by in one case replacing the EGR valve and in the last case replacing both the crankcase ventilation hoses. Work done to diagnose the misfire has included spark plug renewal, coil pack renewal, fuel injector renewal all to no avail. Fuel injector replacement cleared the code for about 10-15 minutes whilst I ran it round the block a few times then came back on when idling. EML only flashing when idling, not an issue when driving - no noticeable misfire really beyond a bit of rough idle. Various gaskets replaced throughout the process too. MOT failure due to flashing EML when idling.

Currently I've been working on the car intermittently over the last 4 weeks or so. Recently when replacing the fuel injector I noticed that there was quite a build-up of oily sludge in the EGR valve pipe and some oil (not much) out the exhaust after putting everything back together and turning it over. In addition, on the misfiring cylinder - one of the intake valves has noticeably different fouling - one clean, one fouled, all other valves on normal cylinders fouled - but it is opening and closing as intended).

Planning on clearing out the EGR sludge by hand / with some solvent but beyond that I'm a bit stuck on the misfire issue - I'm confident its not a head gasket but worried it could be a combination of piston O-ring or leaky valve? Does anyone have any experience on this / advice?

 

[Pigchem]

Hi Jason, thanks for the reply.

1. Compression test is a good idea - thanks. 

2. Not sure if it's got HT leads but will have a look into it.

3. Will look into this.

4. Not that I'm aware of - last owner was a young couple (not particularly into their cars) who had it for a few years so I don't think so. It's not especially fast so I'd be surprised if it was!

5. Will look into this too!

 

Have just gotten off the phone with a garage - I didn't get round to telling him it was a 2.0 petrol before he managed to guess, apparently it's not uncommon for the camshaft (I may have misheard, it might've been conrod?) to be a fault.

Cheers Jason, gives me something to focus my efforts on!

[cliffcoggin]

More fouling of one valve than the others, plus the misfire on one cylinder, plus excessive EGR fouling suggests wear of the O-rings or bore. That's not altogether surprising on a twenty year old car. How many miles has it done? A compression test will be enlightening.

[Pigchem]

Apologies for the radio silence - and thank you for the comment Clifford.

Compress test carried out yesterday - all cylinders were good: cyl1 175; cyl2 185, cyl3 180, cyl4 185. Cylinder 1 is the misfiring cylinder.

Could a leaky valve still be causing the issue? Or does this indicate that the issue might lie outside of the mechanical components? An additional thought its that there might be a faulty valve spring maybe hence the different fouling (see photo)?

[cliffcoggin]

A faulty valve spring is possible, but unlikely. More likely is a worn valve guide allowing oil and gases into the rocker case and crankcase. It appears you have the head off so now is a good chance to remove the valves and check their seats and guides.