Variability in the South Pacific Convergence Zone (SPCZ) is tightly linked to interactions between local convection and large-scale circulation, yet the roles of convectively-coupled equatorial waves (CCEWs) in modulating the SPCZ remain poorly understood.  Using a combined Fourier–wavelet transform, we isolate CCEW signals in daily outgoing longwave radiation (OLR) and quantify their interactions with the SPCZ.  We find that approximately 38\% of the total OLR variance within the SPCZ region resides in CCEW bands, with convectively-coupled equatorial Rossby waves (CCERWs) providing the dominant contribution of about 20\%.  
Wave structures of CCERWs sharpen upon encountering the SPCZ, with convection aligning along the SPCZ axis and exhibiting reduced westward phase speed.  
Detailed diagnostics of CCERW–SPCZ interactions reveal that a convective coupling mechanism involving feedbacks between wave dynamics, surface evaporation, and convection governs CCERW propagation and growth in this region. Southeasterly flow ahead of the cyclonic vorticity anomaly strengthens local trade winds, enhancing surface evaporation.  Enhanced evaporation fuels the growth and westward propagation of convection within CCERWs, with convective maxima located west of the vorticity center.  Latent heat release associated with convection induces a secondary cyclonic circulation that amplifies the wave while slowing its westward propagation through vortex stretching.  This wave–evaporation–convection feedback is further reinforced by the SPCZ background state, leading to the sharpened wave structures observed during SPCZ–CCERW interactions. Overall, this study clarifies the significant role of CCEWs in modulating SPCZ variability and provides new insight into convective coupling mechanisms within CCERWs.