If you mean the smoke it's usually related to the quality of petrol
Unburned fuel in the exhaust system causes the backfire from the exhaust pipe.
The flow of petrol
Several problems can cause high fuel consumption. An engine that needs a tune up, a slipping transmission or a problem with a sensor giving bad information to the computer can all cause low fuel economy.
I will assume you asking about a petrol motor... usually its incorrect timing settings, find out what the timing setting should be, then adjust to suit a leaky exhaust system will also cause this
"lead" is the Pollutant from motor car exhaust that causes mental disease.
No who, but what. All internal combustion engines emit exhaust fumes.
Petrol is a Fossil fuel. It gives out enormous amounts of Carbon-dioxide on combustion. All vehicles use petrol. So it causes environmental pollution.
gas from the exhaust
Broke rings on pistons