weak tach

Question

I have installed an evo one 411 in a 2008 Mazda 3 auto trans and I seem to have a weak tach signal.It does work but I do notice the starer seems to stay engaged a bit after the engine has started.Sometimes it starts and runs for about 15 seconds then quits and the lights flash 4 times.Also  a couple times when testing it the starter stayed engaged for about 5-10 seconds.