Peak spike extraction from a signal

I am trying to extract peak spike from a signal. After extracting that peak spike, i want to calculate its rise time, fall time etc. Amplitude of given signal is stored in 'amp' (column vector) and time is stored in 't' (column vector). My idea is to figure out the 4% of peak value as a starting and ending point of my signal. I have written following code for this;

p(i)=-npk(i); %% already calculated peak value

edgee=0.04*p(i); %% starting,falling edge

[lo,ilo]=min(abs(amp(1:in(i)-edgee))); %% in(i) is the index of peak value

[hi,ihi]=min(abs(amp(in(i):end) -edgee));

Signal=amp(ilo:ihi);

x1=t(ilo:ihi);

For starting point, i am getting right value i.e 4% of peak value. But, for falling point of spike, i am getting wrong value. Anybody here, can guide me please as i am troubleshooting my code from several days. I have also attached pictures of original signal and extracted signal.

[Image Analyst]

Do you want the upwards going spike, or the larger downward spike? Can you attach your data?

[Muhammad Tahir Khan Niazi]

I want to extract a complete downward going spike. Its rising edge should start from 4% of peak value and falling edge should be at 4% of peak value. I am attaching below my data file also.