We introduce the use of fast flat histogram (FFH) method employing Wang Landau algorithm in an adaptive noise sampling framework using random walk to find out the pseudo-codewords and consequently the pseudo-weights for the belief propagation (BP) decoding of LDPC codes over an additive white Gaussian noise (AWGN) channel. The FFH method enables us to tease out pseudo-codewords at very high signal-to-noise ratios (SNRs) exploring the error floor region of a wide range of codes varying in length and structure. We present the pseudo-weight (effective distance) spectra for these codes and analyze their respective behavior.