I've got a 1995 Chevy Lumina 3.1 that is backfiring into the intake.
It make a loud poping noise and if you listen with a stethoscope you
can hear it really loud on the intake. I've checked compression on all
the cylinders (good) and made sure that none of the wires were
crossed. Everything looks good. Can't hear any vacuum leaks but I
haven't checked real hard for that...
It only happens on the No. 3 cylinder. If I pull the spark plug on #3
the backfiring goes away. I thought maybe I had a leaking injector.
From what I understand the coil packs fire both cylinders every time
so I thought maybe the injector was leaking and igniting fuel into an
open intake valve. I tried replacing the #3 injector but no change.
The pinging is consistent but not very rhythmic. There are no codes on
the computer if I remember correctly. What are the chances that I
poped a tooth on the timing chain? I can't see that affecting just the
#3 cylinder. Any other ideas what is causing this?