This group of fuel-saving devices may have had a touch of merit in years past. These special spark plugs, spark intensifiers and related devices are supposed to improve the rate and amount of fuel burn each time an engine's cylinder cycles, reducing the amount of unspent fuel that gets flushed out the engine's exhaust.
In the early days of internal combustion engines, this type of thinking made some sense. Mechanical distributors could develop faults that caused spark plugs to misfire, resulting in one or more cylinders simply pumping unburned fuel through the chamber. Products that enhanced spark plug reliability could improve efficiency in these low-performance engines.
But that type of problem has virtually disappeared in modern engines. Thanks to computerized engine controls and newer, more reliable ignition technology, most modern cars only misfire if there's a significant problem with the engine. There's really no need to enhance ignition reliability: The engine already takes care of that.
Likewise, the claim that an ignition enhancer makes fuel burn faster or hotter is baseless. Fuel will burn at a set rate, regardless of how hot one makes the spark that ignites it. Ignition enhancers might have once been useful modifications, but now they're simply hoaxes to separate uneducated drivers from their money [source: Tony's Guide to Fuel Saving Gadgets].