what can cause a car to backfire...my car does this sometimes and im curious why...

 

Running too rich, timing way off, a bad / mis-firing spark plug, or a combination of all three.

Hope that helps

Mike

 

most likely cause is that you need to change your plugs, because they aren't igniting enough of the AF mixture, or you need to clean your injectors, because they aren't spraying the gas fine enough.

so basically, change your plugs, and dump some injector cleaner in your gas tank.

 

too rich

 

its not plugs cuz they are almost new..why would my car be runnin rich? all i got is i/h/e...nothin major

could it be my exhause causeing some kind of wierd back pressure?

 

Just because the plugs are almost new doesn't mean that isn't part of the problem.... It doesn't take long to foul up the plugs. Take 'em out and inspect them, clean them.

 

damn they better not be bad already..i just paid like 40 bux for oem ones

 

Are you talking like serious somebody just fired a glock backfire or just the little popping noises that all aftermarket exhausts make when you decelerate or let off the gas ?

 

when i left off the gas..it pops, sometimes louder than others...i know it has something to do with the exhuast cuz it never did it until i got it...

 

Now how does being rich cause backfire?

I thought being lean caused backfire. The leaner, the more heat in the cylinder... This is also what causes knock from what I've learned. I don't think running rich causes backfire. I believe it jsut gives you a bunch of **** buildup inside your cylinders and header, as well as smoke from the exhaust. Who knows, I could be totally wrong...

Anyways, I'm running a bit lean, and my car makes a slight pop when I let off the pedal to shift. It sounds normal though.


[Modified by Nameless, 7:11 PM 11/6/2002]

 

What's the difference between backfiring and popping? My exhaust pops most of the time when i release the gas in 3rd or 4th gear. Never had that problem when I was still running the stock exhaust. I am running rich though, the af meter on the dynojet showed an average 12 af ratio

 

It's because gas fumes are building up in the exhaust - this only happens when the exhaust piping is large in diameter. You're probably always gonna backfire, to a degree at least...

With my old motor, my car would make HUGE backfiring pops whenever I let off the thottle, and then tapped it back on immediatly after letting off.. It turns out that the TPS was a little out of whack.

But if yours is only popping when you let off the gas as the rev's are declining, then you'll always have this problem unless you switch to a smaller diameter exhaust piping, or get a motor that has more output.

All of this is considering that your motor is tuned properly (timing, spark plugs/wires/cap&rotor, etc etc).


[Modified by MrTodd, 8:54 PM 11/6/2002]

 

The exhaust has pressure and vaccum pulses. If there is a small exhaust leak, cool air can enter and cause backfires.

 

When ricers put huge grapefruit shooter exhausts on engines that dont need it (i.e. a 2.5 inch exhaust on a 1.6L engine), they make little popping noises. The exhaust has very little back pressure which causes sequential pressure pulsations to suck in cool air and allows pockets of gas and nox to build up. These all cause small backfires and is even worse if the cat is gone/hollowed. This is ok if you are driving a drag car which stays in the high RPM range most of the time. But if you have this on a daily driver it completely ruins the low-end and daily drivability of an otherwise nice car. I would recommend getting a smaller exhaust, unless you drive like an ******* all day everyday, then it will feel a bit more powerful, or if you just like the way it sounds.


[Modified by Dokta, 5:19 PM 11/7/2002]