What causes backfire?

[crankin]

I really just want to know if it is bad for the car. Currently running stage 3ish tune with stock dp and muffler and resonator delete. Every once and while I get a backfire on an aggressive downshift that usually gets ppl ducking. What is actually causing this too happen? Is it too much fuel? Too much timing? Or both? Does it even matter because it sounds cool?

Just wanted to get some opinions. On my Abarth I could actually make it backfire by rev matching on my downshifts (race dp) but with my Fiesta it seems more random like once every 20 downshifts.

 

[JPGC]

I really just want to know if it is bad for the car. Currently running stage 3ish tune with stock dp and muffler and resonator delete. Every once and while I get a backfire on an aggressive downshift that usually gets ppl ducking. What is actually causing this too happen? Is it too much fuel? Too much timing? Or both? Does it even matter because it sounds cool?

Just wanted to get some opinions. On my Abarth I could actually make it backfire by rev matching on my downshifts (race dp) but with my Fiesta it seems more random like once every 20 downshifts.

You are referring to what is called "afterfire" which is a type of backfire, but it happens in the exhaust vice the intake. Afterfire tends to happen when unburned fuel is ignited in the exhaust. You may be a little rich when you lift off the throttle. Mine does it a little too...every once in a while isn't a big deal, but it can get annoying, lol. Now if it is backfiring through the intake, you have other issues.

 

[SpooledUpST]

If it is backfiring through the intake, you have other issues.

LOL yea no kidding! Surge sucks. [MENTION=2052]crankin[/MENTION], as JPGC said. Wait til you go decat dp. I am so excited to get one. Pops and poofs all day long. I notice it on my Stage 1 when i beat on the car especially after a few pulls on higbway, then downshifting hard on off ramp coming up to lights. I get light pops just revving when getting into the garage after driving home.

It is not bad for the car. Richness can affect it but turbo cars generally backfire due to the raw exhaust and unburnt fuel build up in the catback. Enjoy it cuz most people only wish they could get that from their cars. As for Abarths...every single shift seems to cause a pop...gotta love the Italians lol...always a good show.

 

[Hijinx]

My Fiesta has a name, but the name isn't what's relative here because it's nickname is Phoenix. She loves to throw flames. As said, it's unburnt fuel in the exhaust igniting. I'd rather be throwing flames than not. Most especially after a hard run.

 

[crankin]

Sounds like I ain't hurting the car. Good to know.

 

[dyn085]

Watch your AFR during a downshift and you'll see the momentary shot of fuel that you get before the AFR shoots up. It's odd because my FiST does it while my FoST doesn't.

 

[Hijinx]

Dyn085, I'm pretty sure it's for a cooling affect.

 

[dyn085]

Dyn085, I'm pretty sure it's for a cooling affect.

That's entirely possible, though I would imagine the relationship would have been swapped if so. The FoST is the platform with cylinder-temp issues, as noted by the two-step colder plugs supplied with the FRPP tune. Besides, fuel is added for cooling when under a load-it's not really necessary or beneficial when there is zero load and just fresh air being cycled through.

Regardless of reason, it's present and the cause. My FoST doesn't afterfire on downshifts, only on full-load upshifts. I kinda wish it would because the FiST let's out some seriously nasty ones...

 

[Original J-Pat]

So straight pipe is guna be the easiest way to get fire blowing out the ass? lol

 

[airjor13]

Mine "afterfires" alot in the cold Smells stinky and makes me happy!