Diesel powered vehicles have grown in popularity over the last 15 years due to the introduction of advanced, high pressure, direct injection fuel systems that enable improved emissions, power and a more desirable driving experience. However, such vehicles only perform optimally when the fuel system is in a clean condition. When deposits form inside the injector nozzle holes, a measurable deterioration in power is observed. The CEC F-98-08 Peugeot DW10 engine test was introduced in 2008 in order to evaluate the nozzle fouling propensity of fuels and the beneficial effect of deposit control additives. Papers have been published demonstrating such effects, in particular the propensity of zinc and biodiesel contaminants to cause injector fouling and the performance of additives in both deposit control (keep clean) and removal (clean-up) modes. While running such tests with an advanced, proprietary deposit control additive, both the fuel flow (kg/hr) and engine power (kW) measured with the additised fuel were higher than the corresponding measurements made at the start of test with clean injectors running on base fuel. This apparent increase in fuel flow and gain in engine power (beyond the baseline level) was intriguing, so further studies were conducted to explore this phenomenon in more detail.This paper will report on the investigation conducted into this phenomenon, referred to here as ‘power gain’. A series of DW10 engine test results will be shown that confirm that this is a real effect arising from the presence of a proprietary deposit control additive chemistry, and since it is observed with clean injectors, cannot be attributed to the removal of nozzle hole deposits. Alternating between proprietary additive-treated and untreated fuels shows that the increase in fuel flow and gain in power is reversible, repeatable and dependent on dosing with the proprietary additive. Further engine tests have shown that the effect is dose rate dependent and occurs in both mineral and biodiesel containing fuels. Furthermore, neither traditional PIBSI type deposit control additives nor other multi-functional additive co-components show this effect. Further work is now taking place to explore this phenomenon in other engine and injector technologies.