Misfire When Hot?

[Darren93]

Hi all,

I'm having a minor issue with my other half's R56 Cooper S LCI (N18),

I've recently completed the following between myself and a local garage;

Timing chain change including tensioner & oil change
HPFP replacement
Low pressure fuel pump replacement
fuel filter change
spark plug change
Now the car is generally running very well (much better) and gets up to temperate fine etc. but I can feel a misfire once warm.

The car idles incredibly smooth when cold, you wouldn't know it was running if you couldn't hear it.

Once the engine is hot there's a bit of roughness in the idle but no engine code.

Does anyone have any ideas? my guess would be coil packs or Vanos solenoid but I don't want to throw more money at the car guessing whats wrong.

How do everyone else's cars idle when warm?

any help would be appreciated.

[itsnotarace]

Decoke

My misfire was most noticeable cruising on part throttle on the motorway, you put your foot down and you could definitely feel it hesitating before it would pick up

[Darren93]

itsnotarace said:

Decoke

My misfire was most noticeable cruising on part throttle on the motorway, you put your foot down and you could definitely feel it hesitating before it would pick up

I don't think I've heard or read anyone having a decoke on an N18 engine, it's actually quite responsive and drives well. The issue only presents itself at Idle...

It also only has 45k miles on it and maybe uses 50ml of oil per 1k miles

[itsnotarace]

It's direct injection so will suffer same fate eventually

https://www.minitorque.com/threads/does-the-n18-en...

[E-bmw]

Darren93 said:

itsnotarace said:

Decoke

My misfire was most noticeable cruising on part throttle on the motorway, you put your foot down and you could definitely feel it hesitating before it would pick up

I don't think I've heard or read anyone having a decoke on an N18 engine,

Just because you haven't heard of it doesn't mean it isn't true.

It needs doing every 30/50 K miles depending on other factors.

It will look like the image at the top of this:

https://www.northamericanmotoring.com/forums/r56-h...

[stevemcs]

Why did it need all that work in the first place ?

I'd be looking for an air leak.

[Darren93]

stevemcs said:

Why did it need all that work in the first place ?

I'd be looking for an air leak.

It had a bit of a rattle on really cold starts which turned out to be chain stretch.

It also registered misfire codes very occasionally which coincided with HPFP symptoms, since I was doing it DIY I just done the whole fuel system to take care of the new HPFP instead of potentially contaminating the new one straight away.

Does anyone know anywhere in Glasgow(ish) that does wallnut blasting?

Also would the carbon buildup only manifest itself when hot?

[E-bmw]

Darren93 said:

Does anyone know anywhere in Glasgow(ish) that does wallnut blasting?

Also would the carbon buildup only manifest itself when hot?

Google is your friend, there will be plenty.

It can show itself at different times in different scenarios.

Initially it is more evident after warm up (IIRC) due to the initial rate of fueling being more tolerant.

[paultownsend]

Good work doing all that yourself.

Ours liked an occasional misfire. Then it got to the point it would hardly run. Thought it was the HPFP. It was the plugs. Well, one of them. Now they were meant to have been changed under one of previous Mini services under the TLC package. They had not been changed. They were BERU. Thanks Derby Stratstone Mini.

New set of plugs and coils for less than £100 from Opie Oils. Sorted it out. And it ran better than it ever had.

[fatboy b]

Fuelling problem maybe, that’s caused by a sensor. If it’s doing it hot, then the spark plugs could be breaking down as it’s running too lean.