CEL Code - P0301 - Cylinder 1 Misfire

[Mattlock]

Hi everyone,

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

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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.
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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.

[brad]

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

Fair enough but it aint doing no good.

[Transporter]

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.

Well, more like the build up behind the inlet valves disturbed the airflow into the cylinder, which was enough to cause the misfire under certain conditions. So, the compression test couldn't actually find it and mechanic told you what you wanted to here, which doesn't matter since it looks like they most likely fixed the problem for you, at least for some time.

[Mattlock]

Well, more like the build up behind the inlet valves disturbed the airflow into the cylinder, which was enough to cause the misfire under certain conditions. So, the compression test couldn't actually find it and mechanic told you what you wanted to here, which doesn't matter since it looks like they most likely fixed the problem for you, at least for some time.

Haha! Probably very true. He said that the misfire only happened when cold (as I had reported it) because once the engine had warmed up the gunk on the valves was sticky enough to seal everything up!

Their thoughts on the topic are very similar to those of Brad's in that VW DI engines are prone to this. In fact it was a Mk6 GTI the other week that had very similar issues that led them to fixing it with mine.

[themarvel2004]

Hey guys,

Had this happen to me on the weekend too whilst on my way back from the SA cruise (yes, I bailed part way through!) - got some mis-fires while pulling up-hill hard around 4k RPM.
Checked with my scanner and had P0300 & 0301 codes recorded.
Seemed to be running ok later that day with no issues, and same yesterday, but did have abit of a moment at low RPM (like 1800) on my way to work today (just a little bit of throttle when in 6th at around 60kph).

Car is at 100k km, and I don't think it has had a de-carbon done in any previous service (need to double check), and plugs were probably done 5-7 years ago also.

So - would you recommend that I first try a de-carbon process with something like the liqui-moly product?
Then do Plugs if still no joy?
Then do Coil packs if still no joy?

I think I also need to do my DV upgrade at some point soon (probably go a GFB DV+ kit, currently a RevC stock DV). Thought it was that when it happened actually (until I got the code details).

Is doing a carbon clean process just going to make it worse if it is the plugs or coils? Could I end up not being able to start the car at all?

Is there anything else to watch out for using these de-carbon spray packs at home?

Thanks!

[Mattlock]

When my Mk5 threw this error it was cleaned up by hand. I don't know if any cleaner was used on it. The second time it was a runner flap issue rather than deposit build-up.


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