[stashio]

I know this is a topic that's been talked about a lot but my symptoms are slightly different so wanted to check with you lot.

The car cranks fine and doesn't misfire after start up or under gentle/normal driving. Usually it only misfires after it's been driven hard for a while either in sport or manual mode, once it starts missing I can turn the engine off/on and drive gently/normally and it will not misfire again until I put my foot down, etc...

This started a few days ago, misfire on cylinder 1. I've just bought the car and not wanting to throw money at it just yet (I've got 30 days to return it) I replaced the spark plug in cylinder 1 and swapped the coil pack with cylinder 2 - my logic being if the fault remains at cylinder 1 it has to be the injector and if the fault moves to cylinder 2 it's the coil pack.

So I took the car out for a test drive last night and drove it hard for a good 30 mins before the EML came back on - so I did the usual routine, turned the car off/on and drove home normally without any further issues. I've scanned with INPA today which now shows multiple misfires! 3 misfire codes for cylinder 2 (which is where I moved the suspect coilpack originally in cylinder 1) but now 1 misfire code for cylinder 1 and another 1 misfire code for cylinder 6 . Could a dodgy coilpack cause this behaviour? It's clearly suspect but would it cause misfires in other cylinders - like a chain reaction or something?

Normally I'd just replace all plugs and coilpacks straight away but as I say I've only had the car a few weeks so have the option of returning it to the dealer if I'm not happy with it. I love it so don't want to hand it back but I also don't want to be buying a set of injectors either.

The only other code I have (apart from multiple misfires) is P0420 for the catalyst system, it's had that since I bought the car and as it's been tuned I assume the previous owner gutted or swapped out the cat. I doubt it's related but wanted to mention it just in case.

Any advice would be appreciated! Thanks

[dublin14]

Bring it back and thr dealer to fix it if you have the option to bring it back.

[Bimmer Pleaser]

Question unrelated to your problem: how/where did you buy a car that lets you return it within 30 days?

[stashio]

It's a UK thing, you get 30 days of there's anything wrong with the car.

[robprater]

+1 for having them fix it first. I'd start with coils and plugs - probably just do all 6 so I wouldn't have to worry about it for a while. Probably needs to be tuned up anyway IMO - but I typically do that to any car, especially after buying one used because I don't know how it was maintained previously.

[KWX1]

Tuned cars spark plugs only last around 1/5 of the life span of a normally tuned car. Usually when one coil goes the other are not far from failure since they have been subject to the same use and heat. I would say a round of plugs and coils for everyone . You might want to go one step cooler on the plugs and check for recommended spark plug gap on your tune. Cheers