Most DISI engines have special piston designs that direct the incoming air and fuel charge towards the spark plug for a more complete combustion. We've found that this and other DISI features wear spark plugs more rapidly than a normal port-injected engines would. Depending on the level of performance modifications, the standard port-injection engine would be able to run the same spark plug set for around 15,000-50,000 miles. Although, with the L3T DISI engine, we've found that this engine wears spark plugs more rapidly. You should budget on changing the L3T spark plugs at shorter intervals, something along the 5,000-15,000 mile rage.
A wearing spark plug initially exhibits higher boost miss-fires, poor power production, or stumbles under WOT conditions. If you then run a calibration that runs lower boost and the misfires go away, this is an indication of wearing plugs. Some very worn plugs will also create idle and part-throttle miss-fires on various cylinders which the ECU may detect and then report as a recorded miss-fire.
Our data has shown that the factory spark plug temperature range (6) and gap (~.034”) are sufficient for stock boost levels and normal driving conditions. Although, operating the car with higher than stock boost levels or with the calibrations that are loaded on the AccessPORT, require that a spark plug gap of .026” - .028” (0.66mm – 0.71mm) be used on a 1-step colder temperature plug. Denso currently offers this spark plug as part # ITV22 (please be sure to verify each plug is properly gaped before installing them). Our experience has shown that operating your turbocharged engine at higher than stock boost levels requires that your spark plugs be replaced at around 12,000-15,000 mile intervals.