All you need is good quality spark plug wires. When it is loadshedding or dark at night, open the hood of your car, start it on CNG and see if the current is visible moving through the wires, if so, then you need to replace the wire because it means that current is leaking. However, if you switch to petrol, you will not see the current leaking. I have experienced this on CNG (as was the case with my previous Khyber).