Slight misfire - not leads, plugs or coil pack...

[sam55]

So my car appears to have a slight misfire on cylinder 2 (by slight, I mean that it appears to be firing weakly). I changed the plugs, coil pack and leads but the problem didn't go away. Then oddly, according to my OBD2 reader the misfire shifted to cylinder 3, before shifting back to cylinder 2 again after a minute or so of running.

I tested cylinder compression and all cylinders are within 5psi of each other. If the weird misfire shift hadn't happened, I would have assumed this was an issue with cylinder 2's injector. But now I'm stuck.

Is it possible there's a build up of something in the fuel rail?

 

[N4TH4N]

Dodgy injector?

 

[sam55]

Yeah that's what I thought, but then cylinder 3's temporary involvement has made me think otherwise.

 

[bloke]

injector is the only thing that will bring up a specific cylinder misfire.

 

[dangerous dave]

Injectors are failing a lot these days, they're old as fook..

 

[dann2707]

How does the ecu know it's a misfire?

 

[sam55]

Thanks for the help guys. I switched both cylinder 2 and 3's injectors for new Magneti Marelli ones. Problem fixed.

@dann2707 I used an OBD reader to diagnose that it was related to the ignition. It also told me the issue was in cylinder 2 (and occasionally 3!).

 

[STEVE.M]

Thanks for the help guys. I switched both cylinder 2 and 3's injectors for new Magneti Marelli ones. Problem fixed.

@dann2707 I used an OBD reader to diagnose that it was related to the ignition. It also told me the issue was in cylinder 2 (and occasionally 3!).

Thanks for posting an outcome.
An opportune moment to remind folk no1 cylinder is the gearbox end of the engine.