Diagnostics !!!

[cobracars]

Hi folks...i have red mk2 octy vrs 2.0 tfsi, it had a decat downpipe and mot is due soon ish...so i put proper cat on it and full stainless from cat back so as it will pass mot on emissions hopefully, and obviously to put EML out, so put the OBD II on it to clear the light from dash which is now done...but it found another fault saying misfire in cylinder 3 !!, will it just be a spark plug or lead OR something else ??, any info wld be appreciated thanks

[Baroket]

It's impossible to give an answer just based off of a cylinder 3 misfire.  It could be either the coil, spark plug or the injector.
If you have a set of torx bits, a spark plug socket and an hour you can do some diagnosis by first swapping the coils from cylinder 2 & 3.  If the fault goes from cyl 3 to cyl 2, then it's the coils - I'd replace all 4.  If the fault remains on cyl 3, then swap the spark plugs.  If the fault moves, it's the spark plugs - again I'd replace all four.  If after doing the above, the misfire is still persistent on cyl 3, then it'll more than likely be the injector.  If the fault does turn out to be an injector, then it will be a rather expensive repair as the injectors alone are around £300 each.
Speaking from experience the cost of replacing the injectors at a VAG specialist cost me around £2500.

[cobracars]

Thanks very much for advice...iv not had car long tbh and think spark plugs have been changed as x4 old ones in boot...so must b either coil pack or injector ??, knowing my luck will b the later !!!, is it a big job to replace injector ??, thanks 

[cobracars]

Hi..can anyone tell me what the gap on spark plug shld be for my octy vrs 2.0 tfsi as iv done some research and apparently if gap is too big this is what causes missfire on this engine when cold ?, gap needs to be 3000 or 7th of an inch is that correct ?