Last weekend, I swapped out the Apexi Noir exhaust on my FD for a Racing Beat dual. First impressions are that (1) I really like the stock-like yet aggressive look of the Racing Beat, and (2) the RB is quite a bit louder than the Noir. This seems inevitable since the Noir is more like a OEM exhaust in that it is chambered, not straight through, whereas I am assuming that the RB is a straight through design.

The increase in sound is not bad, and actually it sounds pretty good to me, but what came with it is a noticeable backfire during some light throttle upshifts, and also some other times like if I rev it a bit while warming up the engine. I found that for some reason the 2 to 3 upshift seems to be the worst offender, with a single loud pop on the clutch-in point if I am accelerating lightly, and much less backfire sound if using more throttle before the clutch-in. Don’t hear anything during hard acceleration shifts.

I think my car was always backfiring, but the design of the Noir silenced the backfire due to the chambered design and I never heard the sound. I did notice similar backfire when doing the warm-up revving, but it was very subdued, almost unnoticeable whereas now it is a strong “pop” sound.

Currently running stock ECM, air pump and air pump mechanism, stock airbox, OEM main cat with JDM OEM downpipe. I’m guessing that the backfire is due to the air injection into the engine port that is occurring at idle and small throttle angle, and maybe the AICV is too slow to respond to closed throttle or there is residual air in the system. Car runs great otherwise.

So my question, is this normal behavior for a stock emission setup with a non-chambered muffler? Or is my AICV acting up perhaps, and not controlling air switching away from the port as it should? Sorry if this has been answered before, but I did not see it specifically in a search so I thought I would throw it out again anyway.

Thanks!

 

Mine also backfires on occasion - I actually like it.

 

How old are your plugs? May just be worn plugs and car running richer than usual.

I agree, I think it was probably doing it with the Noir but it was masking the backfiring.

Is the air pump actually running? If the connector is broken or the fuse is blown you could have the air pump but it's not actually working. With the car idling you should see the pulley spinning, and it should engage/disengage as you rev the throttle.

Dale

 

Thanks for the replies.

The airpump system is fully functional, and the airpump clutch opens and closes like it should based on the FSM (at least as far as when the engine is revved up in neutral).

The plugs have about 1500 miles on them, they are standard-style NGK platinum 7 and 9 heat range (maybe iridium, I forget…got them from Rock Auto but they are not racing plugs, just street perf. style). Also have the SBG smart coil setup. I can check them though, that is easy enough and low cost to experiment with new replacements.

The O2 sensor also has about 1500 miles of use, but I wonder if it is reading a false lean condition and forcing a rich shift? However, the NOx numbers I see at smog check time are a little high and CO/HC are basically zero so that would point to lean not rich... Unless port air is always flowing into the engine which could depress CO/HC and elevate NOx, and maybe cause backfire... Only way to check that though would be to pull the UIM and troubleshoot. That's more work than I would like to take on right now...but maybe would do in the future if the consensus is that what I am seeing now is not normal.

 

Delete...duplicate post :-/

 

Your ECU/O2 sensor only corrects the a/f ratio during idle and cruise, so I doubt that's it.

Personally, any time I get rumble/pops I look at my a/f gauge and can tell that it's from a rich condition while not under load. So, unburned fuel in the exhaust. It's common and I wouldn't sweat it.

 

I ran into the same problem when I replaced the stock cat-back with a PFS unit which is straight through. The backfiring went away when I leaned the idle down. I think the backfire is inconsequential, if not annoying, and agree that it was likely there all along.

 

AFAIK, most back firing comes from rich a/f and retarded timing. If its throttle off then likely rich a/f. You can fix this via tuning or adding another cat to your exhaust system. However, depending on the situation, some backfire is will occur no matter what you do.

-groovin

 

Thanks guys, its not so bad actually. I suppose some backfire is normal for a rotary and having a straight-through style muffler will transmit the sound of these directly. I'm running a stock ECM now so no changes possible, but I will be reinstalling my PFC soon and have the car tuned so I'll mention it to the tuner and see what they say.