Defending his WBO Jr. Flyweight title for the second time, Dieppa suffered an injury product of accidental headbutt in the second round, which led to the fight being declared a technical draw. For the next year and a half, Dieppa had a series of problems, including some injuries and ongoing managerial disputes. The World Boxing Organization considered stripping him of the championship, but decided that Dieppa was unable to defend the title due to matters outside of his control. On March 20, 2004, Dieppa participated in his third title defense, against Colombia's Kermin Guardia in a fight held at the Mario Morales coliseum, in Guaynabo, Puerto Rico. Dieppa won by knockout after one minute and fifty-one seconds of the round had passed. Guardia announced his retirement immediately after the fight. Dieppa's next defense took place on July 30, 2004, in a card organized in Louisville, Kentucky, where he fought against Ulises Solís. Dieppa retained the title by a majority decision, with one of the judges scoring the fight 114-114 while the other two gave scorecards of 120-108 in favor of Dieppa. On January 29, 2005, Dieppa fought against Alex Sánchez in a fight that took place at the Rubén Rodríguez Coliseum, in Bayamón, Puerto Rico. Prior to the fight a number of promotional events were organized. Sanchez had an early advantage in the fight, relying on his boxing skills. In the eleventh round Dieppa won by knockout after connecting a solid combination. This fight was named the fight of the year in Puerto Rico by the local boxing commission. On April 30, 2005, Dieppa lost the light flyweight championship against Hugo Cázares. The fight was stopped in the tenth round with Cazares receiving a technical decision victory. On December 17, 2005, Dieppa returned to action versus Juan Alfonso Keb Baas in an event organized in Fajardo, Puerto Rico. Dieppa won by unanimous decision and won the vacant WBC Continental Americas Jr. Flyweight title. On May 26, 2006, Dieppa fough against Eric Ramírez of Mexico. In this fight he focused on using his boxing skills to counter Ramírez's aggressive style. Dieppa received identical scores of 97-92 from the judges. On March 23, 2007, Dieppa lost by divided decision against Daniel Reyes. Following this fight, Dieppa defeated former champion Alex Sanchez, and lost by unanimous decision to Iván Calderón for the WBO's championship.