CEL Code - P0301 - Cylinder 1 Misfire

[Mattlock]

Hi everyone,

My GT is starting to show a Cylinder 1 misfire one a more regular basis.

============
History:
I got the code the day after I picked up the car and had it scanned. It wasn't checked much more than that other than to keep an eye on it if it comes back.

It then returned for a second time almost exactly a year later (in June) as the weather started to be cooler in the mornings.

I got it a third time (1 flash) but it never logged a code.

It came back again today for about 15 seconds and then went out. That equal four times in 13 months.
============

It only seems to happen in colder weather and particularly after the car has not been used for about 24 hours (like this morning).

I'm not sure if it is a vacuum problem (my OBD-II software seems to show typical vacuum/boost changes whilst I'm driving but I suspect this is reading the pressures at the DV) or a spark plug on the way out.

Is it worth changing the spark plugs or should I book it in for inspection?

M.

[Snail Style]

Get it compression tested, replace plugs if they are due or swap them around and swap the ignition coils around as well. Make sure you note where you moved cyl 1's coil and plug to.

Take it for a drive with VCDS and monitor MVB's 15 & 16 in engine, see if the misfire has moved.

[Mattlock]

Cool. Thanks. I've booked it in to have it looked at.

The spark plugs were changed on schedule at the 60k service (which was before I bought the car).

[Mattlock]

So a compression test found it! The fault was caused by the build-up of sticky residue meaning the valves didn't seal properly when cold, causing low compression and a misfire.

A intake manifold clean has fixed it and the car feels smoother and revving easier as well.

[brad]

You should be doing some form of regular chemical or water mist intake clean if you are getting build up to the extent that it holds the valves open.

[Mattlock]

Yeah, I discussed that with the mechanics yesterday. I think that part of the problem here is that I bought the car with 92k on the clock and I have no idea what quality/grade of fuel had been used in it before now. With 108k on the clock now it's not done too badly but it will be getting regular attention for here on in.

[brad]

The fuel wouldn't make any difference as it's direct injection so the fuel doesn't go near the inlet..

There are a few threads about inlet maintenance. Worth a search.

[piper26]

The fuel wouldn't make any difference as it's direct injection so the fuel doesn't go near the inlet..

There are a few threads about inlet maintenance. Worth a search.

It still has a slight affect. If the fuel doesnt burn correctly carbon builds up on the injector, piston, valve etc. This then creates over time more carbon build up and 'wet' spots. These spots mean that the chamber is not burning efficiently or hot enough. The oil vapour in the intake from the pcv system can leave deposits on the valve seat as it is not burning in operation.
Would have to be run on poor quality fuel or oil for some period of time to get to that point though.
But as more carbon deposits then the effect is increases

[brad]

It still has a slight affect. If the fuel doesnt burn correctly carbon builds up on the injector, piston, valve etc. This then creates over time more carbon build up and 'wet' spots. These spots mean that the chamber is not burning efficiently or hot enough.

OPs issue was oil / carbon on the inlet valves.

The oil vapour in the intake from the pcv system can leave deposits on the valve seat as it is not burning in operation.
Would have to be run on poor quality fuel or oil for some period of time to get to that point though.
But as more carbon deposits then the effect is increases

About 100,000km give or take 10% is when most VW DI engines seem to need a de-carbon of the inlet valves, no matter how good the fuel or oil is. Been there / done that.

[piper26]

You still have fuel vapour in the intake system via the charcoal canister and n80 valve.