backfiring!
 

I have a 00 Civic Si with a greddy turbo+intercooler, aem fuel modifications, walbro fuel pump, greddy catback exhaust and a straight pipe that replaced my cat. My engine is throwing these codes: fuel system too rich, and fuel trim malfunction. My car has started to backfire slightly with change in rpms usually between gears or downshifting. I also have a VAFC II installed, but not tuned at all yet. Anyone know why this is happening? Thanks.

My 02 civic with headers intake exhaust hi flow cat is doing the same thing just use that v-afc to tune the car so it's not runing so rich and i think with the backfiring it's just straight through with no back pressure so thats normal. My car was throughing the code too rich too. Hope this helped

most likely cuz of your fuel mod and fuel pump.. thats why your running rich.. plus you didnt tune with the VAFC yet.. the backfire is cause by not having a cat.. I kno my buddies with subarus backfire.. with their turboback exhaust.

Sounds like you are running too rich. All your fuel mods need to be re-adjusted. If you know how to adjust them lean it out a little bit.

I've heard that you can't really tune the vafc without a dyno very effectively, so I'm gonna try to find a shop that has a dyno. Is it possible that the backfiring might stop if I get my fuel leaned out a little bit and possibly less airflow with the vafc? Thanks for all your advice, it really helped a lot...

I thought the VAFC was just for v-tec adj. If there are fuel ratios in there as well then yeah that needs to be looked at too. I dunno if the back firing is due to not having a cat. Thats usually occurs if the car is running too rich, which it obviously is.

Why cars backfire - A car backfires because unburned fuel is getting to the muffler. The heat of the exhause system causes the fuel to compust, thus a backfire.

Just looked that up.

i knew the loud noises coming out the back end had somthing to do with gas......... AAAHAHAHAHAHAHHAHAHAHA

ps.. that was my first car joke.. i think its great

backfiring!
 

I never actually knew why a car backfired. I assumed it was from built-up back pressure or because the catalytic converter was fried. That was very helpful. Thanks again everyone!

moved to the Vehicle Issues / Problems forum

technically this should go into the Previous Gen Civic's forum, but i put it here to get more exposure

the apex'i Vafc controls vtec, and air fuel.. Vafc= Vtec air fuel controller.. i think lol but it makes sense.. haha