Hi Guys,
My QQ J10 petrol has developed an issue where it is very difficult to start and then runs rough like it misfiring even on idle and sometimes conks out. Runs really rough when driving. It indeed has code P0300 which indicates random or multiple cylinder misfire.
Tested cylinder compression and that is fine (had a top end rebuild a few months ago)
Tested all coil packs and they are ok.
Tested plugs and on inspection these were quite black and tips worn. I replaced them with new.
Tested injectors and found one of them was giving way to much fuel so replaced. (This is probs what caused me to have to get the top end rebuilt due to burnt valves).
Tested - fuel getting to injectors and seems ok but have noticed that when I open the tank cap I'm now not hearing the rush of air that I used to get which may or may not be related as fuel seems to be pumping to injectors ok.
I'm now stuck as can only imagine that it's either fuel pressure (but injectors seem to fire ok and spray patterns look ok) or air mix somewhere due to the plugs getting blackened. Having said that they could have still been black from before engine top end was rebuilt.
Would fuel pressure or say O2 sensor throw an error code other than P0300?
Any ideas what's going on and what and how to test any remaining possibilities e.,g O2 or fuel pressure etc?
