My Mac doesn't boot cuz I wash the motherboard with petro.

Time to find someone with a large enough ultrasonic to hold your board. You want to use a variable frequency unit as it will be able to more effectively remove the petrol.

You’ll need to use a solvent which can cleanse the petrol which is non flammable and don’t have dangerous vapors in the ultrasonic.

You may need to research and experiment a bit to figure out what you can get. If you can’t find anything thats non flammable use the ultrasonic cleaner outside and have an fire extinguisher handy just in case!

Otherwise its time to replace the logic board.