Hi, can anyone help me with a prob? Have got a 93 impreza WRX and it had been run on a mixture of helicopter and unleaded fuel previously. Black soot out of exhaust while under full boot? Turbo has slight oil about it. plz help!!

 

Lambda sensor probably damaged by leaded aviation fuel, which would then cause probably overfuelling off boost. On boost though is a different matter.

 

Running on a mix with helicopter fuel will coat everything in your engine with a lead oxide deposit, as John says the Lambda sensor will be affected as will any catalysts in the exhaust system and these will need replaced due to coating with lead. A build up of carbon in the exhaust would be inevitable as avgas is basically a paraffin and wont burn very well in a petrol engine. It may well be that this is just blowing out when the gas speed is sufficient, other than that black smoke normally dictates overfuelling.
Beastie