2010 1.2 3 cylinder misfiring issues

[Overtheline92]

Hi

I own a 2010 3 cylinder 1.2L vw polo that has issues with misfiring. It started about a year ago, the car would idle badly and would suffer from a loss of power when I put the throttle down heavily. I changed the spark plugs but the issue persisted with it then cutting out completely on the test run when they was fitted (1 year ago). The plugs were ngks and according to them should have 1.1mm gaps.

I changed the gap to 0.8, and the problem went away so I thought nothing more of it. This week I did a long motorway journey and when I parked up the car was idling badly to the point where the whole car was like a roller coaster. The new plugs have done mine 10k since they were installed so they should be fine.

I decided to buy some new ones anyway since it's the cheap option to do and again I had to reduce the gap to 0.8 to get the thing running correctly. However this time I'm still struggling with power in certain situations most of which include hills.

The plugs appear to be running rich with the third cylinder (right hand side if looking at the engine) being pitch black compared to the other two. What could be causing misfire still? Clearly the plugs are compensating for another issue but I can't figure out what it is. Car has only done 65K but most are motorway miles due to my job.

I have a diagnostic reader on its way tomorrow as the engine light is now on. However would like some opinions if possible

[iichel]

Preliminary diagnoses are a lot easier with the info from your scan tool

[Overtheline92]

Right so i bought a diagnostics tool and plugged it in, as predicted it showed the result "p0303 - cylinder 3 misfire" . As stated before ive had to reduce the new spark plugs from 1.1mm (recommended) down to 0.8mm in order to effectively get it running to some extent, now the most it will misfire or experience a loss of power is when idling or when under heavy power or full throttle (hills are far worse).

again with the third cylinder the plug is far "blacker" than the other two,

my next idea is to maybe replace the fuel filter, in case its being starved or similar (again a reletively cheap option), can anyone with experience shed some light on this? im utterly confused as to what it might be

[iichel]

is that the only DTC?

[Overtheline92]

Yes it was the only code present when i run a check, i erased it, and it now no longer comes up (i presume since i am running the sparks so low)

[RUM4MO]

Maybe you should try swopping the coils from 1 >< 3 and open up that plug gap again, doing that should rule out a weak or failing coil?

[Overtheline92]

Update -
I had the engine code "P0303 - cylider 3 misifre" come up again, so i decided to revisit it and do a thorough inspection. I can't believe i missed it before, but i found that inner wall on the third coil had receeded excessively. I hope that a new one will resolve the issue, however i dont understand why this particular cylinder coil has suffered such high degredation compared to the rest? should i be worried ?