In this paper, the concatenation of modified phase precoding on a spiral curve technique and new trellis coded modulation (TCM) is proposed for application in the frequency selective slow fading channel of wireless communications. Simulations show a significant improvement of the total gain compared to those of the conventional post-equalization of sub-optimum soft output equalizer (SSE) with the same TCM schemes. The modification on the original spiral curve-precoding gives 0.5 dB of gain over the whole range of signal to noise ratio (SNR) including the overcoming of signal amplitude fluctuation in a non-deep fade channel. Next, new TCM codes by the symbol mapping method perform better than the conventional TCM in both of AWGN, and in intersymbol interference (ISI) channels with precoding. The performance of this proposed system is further improved achieving a few dB of gain by the application of soft output detection to each of the codes. A theoretical analysis is carried out to verify the simulation result and found that they match quite well. Finally, the additional result of an adoption of a simple turbo code confirms the success of this ISI combating model as well.