Hi guys, I just bought a fairly stock FD rx7, the car is stock except for an apexi filter.

The air pump had loud Mooo sound during low rpm let offs. But when I added in the silencer, the air pump would Mooo much louder during acceleration and on decel. The noise seems to be coming from the intake tube of airpump, rather than the exhaust tube where I put the silencer.

Another issue is low rpm backfiring, this occurs especially during fine movement when you slightly blip the throttle, the car will pop and backfire.

I also noticed the rear bumper near the exhaust area is really sooty, much like running a decat FD.

I changed the spark plugs, no change.

When I pulled the airpump connector, all the moo sound went away, as well as the backfiring issue. Low rpm respond seems to improved also. The car would always hesitate during take off with the airpump plugged in.

Could this be a bad airpump? clogged cat? faulty ACV solenoid?

Any help or direction would be appreciated.
Thanks guys

 

Not to state the obvious but, you may need a new air pump. Aftermarket intakes that get their air from the hot engine compartment accelerate the deterioration of the air pump. See the following service bulletin:

 

The silencer goes on the intake side of the air pump.

 

Thanks for replying guys, the silence was placed correctly. Just want to double check whether it could be something else before buying a new pump.