i used to toy around with my programmeable ecu on my previous
car and initially, the fuel curve was all wrong. while my fren was
driving behind me, he told me that there was this "pop" sound and
some flames coming outta my exhaust each time i full throttled to
redline and released. found out after pluggin in the A/F meter that
my mixture was too rich and the excess fuel in the exhaust were
probably still burning by the time it exited. very bad for the
exhaust valves and ports of your engine head...... 
