Error code P0303 misfire in cylinder 3
 

The wagon performed well on track, with stable temperature and no obvious problems. But after sitting for an hour or so before leaving for home, when I started up again the check engine light was on.

Idle was a bit lumpy but otherwise no worries. The light was still on when I got home and I have since used a choice reader to check the ecu, and it came up with error code P0303, which seems to mean misfire in cylinder 3.

I cleared the code and started the car, and the light didn't come back on. Haven't driven anywhere in it since, but do you guys think I should forget about it unless the light comes back, or do some investigations?

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I'd get it checked out, ask some one to take a look to be safe, Someone could read the ecu and check what the state of things is relatively easy.

What sort of things would be checked, or looked for? Just thinking if I can read the ECU myself then it will save hassle.

If you've got a tatrix cable you could read The current corrections the ecu is making if any (anything serious will show up as dropped multiplier and loads of timing pulled etc) ,

Could be ignition coil, plug or injector issue if nothing mechanical


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Not saying it is but I had no po303 on the bug and it ended us being the neutral position switch

Went out at the weekend and the light came back on, lumpy idle again.

Will check the plugs, I don't know what kind they are but I suppose it/they might have got gunked up after the high load running on track.

Swap a coil pack around and see if the problem moves with it, also easy enough to do


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I swapped the coil packs over, cleared the code, and it came back with the same code (misfire in cylinder 3). So it looks like I need to check the plug.

Has anyone got any tips for how to get the plugs out? They're in such an awkward place with no line of sight and very cramped access. I've got a standard plug spanner with a universal joint in the handle and a T-bar on the end, but couldn't tell if it was locating on the plug. Is there anything special about the plug type?

Sounds to me like you may have screwed the engine, I'd check plugs but compression test it at the same time

You need a proper plug socket short extension and ratchet, remove airbox remove washer bottle, and it's fairly easy

Yep thanks, I've had the airbox off to do the coil packs, but didn't know what size the plugs were - now I know they are 16 mm and my plug spanner is for 21 so have ordered another one!

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OK, got some new plugs and a 16 mm plug spanner, a bit of huffing and puffing and I got the old plugs out last night and replaced with new NGK PFR6Bs off eBay for £27. Only did cylinders 1 and 3 so far as I ran out of time.

Old vs new plug in the pic attached.

Put it all back together, started up and it was all smooth. Cleared the CEL code and it hasn't come back, so think that's the end of it. Will change the other side next week.https://uploads.tapatalk-cdn.com/201...6f450ccb0e.jpg

That's a fair size gap on the old plug, no wonder it was missing a bit, how many miles do you reckon were on them?

Who knows? They haven't been changed since I got the car 16k miles ago, but no idea how long they were there beforehand. I'm guessing since they were Bosch and not NGK they are at least the second set the car has ever had.

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