Recently, I changed the spark plug and wires in my FD and I noticed a very subtle sound coming from my exhaust.

It sounds like a bass note that would come out of a subwoofer. So, its very low pitch, sorta like a thud sound. It doesnt sound like backfire either.

Oh yeah this only happens at idle and low rpms. Is this pinging or knocking?

I appreciate any help thanks

 

A ping or knock will have more of a metallic mid-to-high-pitched tone to it. Like striking the inside of your engine with a large ball-peen hammer. And usually by the time you hear it, your engine's done.

 

OK thats good to hear. thanks.

however, i wonder whats going on with my car then, are they MINI backfires???

 

also i dont think i have ever noticed just one they come in a series, like marbles in a tin can. think annoying snata clause costumed guys in front of stores at christmas time...

 

...on crystal meth...

 

It's possible. Is your car modified? Are the sounds coming from the rear of your car, or definitely the engine bay?

 

My car is very close to stock. I dont even have a DP yet. I have AST and new plugs and wires.
I noticed the sounds after the wires and plugs got installed.

You can hear it out the exhaust but I think its coming near the engine area. Maybe my precat is being dumb? I do have a DP, just not installed yet. I swear, they sound like realy tiny backfires.

I was thinking my trailing plugs could be crossed but I checked them before putting the throttle body back and stuff, so the wires should be installed correctly.

 

oh yeah, they definitely dont sound anything like marbles or hammers

 

It's probably just some gases exploading in your pre-cat or downpipe or something..
I wouldn't really worry about it..

 

yeah other than that the car is good, and my turbos are giving me the 10-8-10 boost. I'll put the dp in this weekend, thanks

 

It's called after-burn. All RX-7's do this because they run so rich and so hot. They have a thing called an "anti-afterburn" valve that's suppose to help eliminate this. It was part of the BAC valve on the 2nd gen and part of the ISC on the 3rd gens.