FFT() Application for a real sound data

    He! everybody

      I am Tesfaw

   I am confused to do my project on signal processing and I need help fro the 

    forum.The project is to determine the fundamental frequency of a Toyota 

     engine sound(idle) using user defined codes. My attempt is below.

    Ns=samples=131072; 

    Fs=44100; %sampling frequency

    %channel 1 ,data type double in .wav format

    [z,Fs]=wavread('normal.wav',131072);

     N=length(z);%length of the recorded sound 

     %conversion to binary

     b=bin2dec(fliplr(dec2bin(0:N-1)))+1;

    %make it bit reversed order

     MC=y(b);

     s=which('normal.wav');

     set(gcf,'color',get  

(0,'DefaultUIcontrolBackgroundColor'),'NumberTitle','off','Name',s,'Resize','on','Menubar','none');

    %calculate the frequency

    fr = (0:(N/128)-1)*Fs/N;

    p = abs(MC(1:N/128));

    [Amax,f] = max(p);

    fprintf('Max.Magn. of Amp1. is %6.4f db/n and the freq f is %

     4.2f\n',Amax,f);

    pp=fftshift(p);

   %plot the figure

    plot(fr,pp,'b') 

    I need to determine the Amax(maximum amplitude) and the frequency 

       at which Amax occur

      but the result from  plot and from fprintf code is not the same

      Please corret me 

      I am thankful for any help ! 10Q