If diesel is used in a petrol engine, it can cause serious damage to the engines internal components. The following are some of the consequences of misfuelling a petrol engine with diesel:

• The fuel filter may clog up because its not designed to handle the greasy property of diesel.
• The fuel injectors can clog up due to the mixture of petrol and diesel.
• The spark plugs may fail due to the soot build-up caused by the mixture of petrol and diesel.

On the other hand, if petrol is used in a diesel engine, it can cause the following problems:

• The petrol may not reach the engine due to the clogged up fuel filter.
• The engine may misfire, stutter, and stall.
• The drying properties of petrol can damage the engine components, especially the fuel injection pump, which relies on the lubricating properties of diesel.

Its important to note that the magnitude of implications may differ as per the engine type - petrol or diesel. If you accidentally put the wrong fuel in your car, its best not to start the engine and seek professional attention to flush out and remove the toxins.