Need advice re periodic misfiring
 

I have a 2005 rx8 that has been run on Caltex 98 , MRO and always serviced as per the manual. On 2-3 occasions over the past 18 months it has developed marbles in a can sounds at about 6000 rpm and loses power. This only occurs on extremely hot days when the car has been driven for a long time. When the car cools there is no problem at all and it drives faultlessly on all the days in between. the coils, wires and plugs have been changed, but the problem still occurs on very hot days.

I notice that the plugs used in Australia are heat range 6 for leading and 9 for trailing, whereas they are 7 leading in the rest of the world. Do you think that in hot weather the 6 range plug could be causing pre ignition or do you think there is another problem with the car?

Provided the plugs are clean and coil and wires are functioning, the symptoms could be related to losing compression. Before that you should reset the ECU. There is a hard reset which I had to look up - but turn the key to ignition first and press brake paddle many times.

I don't think the heat range is related to outside (ambient) temperature. It is more related to engine temp. The cooler plug get rids of heat easier, but they expires sooner. I have less hesitation at high end after using the 9L10T setup but hey I have at 9000rpm whenever the engine is warm (hehe track car's fate).

Sounds like the symptom is intermittent ... I suggest you overhaul the wires and plugs again. I manage to cover them with carbon shit after 10000km of tracking/driving. It feels 10x better afterwards.

May have to get a rotary person to do a compression test too.

Might want to check your fuel pump as well....