Thanks for your attention for this question. I want to know why my result of modification indices was empty. Could it be induced by my limited sample size (n=8). If so, how could I improve my model fit with data of small size?
We investigated how changes in these parameters affected sample size requirements with respect to statistical power, bias in the parameter estimates, and overall solution propriety. Results revealed a range of sample size requirements (i.e., from 30 to 460 cases), meaningful patterns of association between parameters and sample size, and highlight the limitations of commonly cited rules-of-thumb.
because the number of your sample is so small and you may not allowed to use sem, there are another technics that may help you in interpret the data like correlation or even using t-test.