The pressure- and temperature-dependent rate coefficients for the isomerization and decomposition of alkenyl radicals of 2,4,4-trimethyl-1-pentene (JC(8)H(16)) were obtained using the RRKIVI/ME method. The potential energy surfaces (PESs) were calculated at the DLPNO-CCSD/CBS//M06-2X/6-311G(d,p) level. Uncertainty analysis of dominant reactions was conducted. In addition, the Metcalfe model was modified using our calculated rate coefficients. As shown by the results, isomerization reactions are dominant over the low-to-intermediate temperature range, while decomposition reactions are significant above 1400 K. Pressure has a significant effect on the radical stabilization reaction. With an increase of pressure, the formation of JC(8)H(15)-C from JC(8)H(15)-A becomes more important. Finally, the updated rate coefficients have little effect on simulated ignition delay times. However, the modified mechanism could provide more reasonable flux in the low-to-high temperature range.