hi i have a 94 chevy Astro van awd 4.3 v6 and its backfiring through the intake only when you start going up hills is the only time is does it. I changed the spark plugs, wires, cap,rotor, and coil. check engine light is not on. any suggestions

 

Only thing I can think is that the injectors are leaking in the intake manifold. Or timing is way off.

 

Thanks. I will check it. what would also cause the Exhaust to get cheery red with no cat or muffler on it. Only on the passenger side. 94 chevy Astro van awd 4.3 v6

 

Over fueling I'd say.

 

k. Thanks.

 

HI,There is a TSB about the ignition module that will cause backfiring we
replaced it on my sons 94 s10 and that problem went away,now we are trying to bucking from i believe fuel starvation,but there is not a schrader valve on this year truck to check fuel pressure with a gauge.