hamstrungtaco

alright, i just put downey header on my 2.7 taco and already have a magnaflow with 2 1/4" dia pipe which is the size downey recommended. 5 mins down the road the check engine light pops on and its constantly distracting me, im curious if anyone has had this problem with the same or similar setup ive done, or if the computer has to be re-flashed