backfire sound

What is causing this i guess you would call it backfire? I dont really know how to describe it so i'm just gonna post this video. (http://www.youtube.com/watch?v=oAMcaCSJdN8)

the tailpipe is just off the top of the screen, somehow the sound got behind the video and that little puff of stuff that comes out is right when it makes that backfire sound not when its revving up like in the video. Its a 98 blazer LT with 83,000 miles. I just changed out the fuel filter and pvc, if that would make any difference. I never remembered it making this sound before.

Much Thanks,
Josh

It sounds like a aftermarket exhaust with little baffling to me! anyone else?

It looks like you have fuel still burning in the exhaust . Maybe a plug not firing every cycle or a litte rich . Is that cold condensation on the ground or was the engine completely warmed up ? At night , can you see flame ? cool if so . Exhaust valve openning too early ? rocker arm too tight ? Good luck , Rob

It sounds like a aftermarket exhaust with little baffling to me! anyone else?

I agree. I deff has a deeper idle than stock, just the way mine 97 w/ a flowmaster sounds. It to gurggles like that when the rpms fall from me reving it a lil.

i'm due for new plugs, thats probably what i'll try next. but yeah thats the stock exhaust. Although i'm not sure how good of a condition its in, it seemed louder after driving through some water one day and has a few dents in the muffler but i cant find any cracks so who knows? I'll hopefully be getting a Flo-pro exhaust here in a few weeks, i'll post another vid if I do.

I don't deem that backfire. I have heard perfectly tuned engines pop like that when the rpms are falling.

It could be anything really including a little water in the muffler.

Try drilling a tiny hole in the bottom rear of your muffler at the lowest point below where the tailpipe attaches to the muffler.

This will remove any water in the muffler and also extend the life of it as well.

Typically a backfire on deceleration is associated with a system that incorporates an air pump, (A.I.R. or air injection reactor). However, 1998 Blazer is not equipped with that system. The AIR system is designed to pump fresh air in to the exhaust manifold on acceleration and cruise only. If the diverter valve fails, it will allow fresh air into the exhaust on deceleration also, causing a series of small backfires. When the relatively cool fresh air is introduced to the hot, fuel-enriched exhaust, a “thunder storm” of sorts happens. If you have been around a vehicle with open headers, they backfire on deceleration also. Same principal, very short exhaust pipes and the exhaust does not cool down gradually, as it does in a full exhaust system. Point being, I would look for an exhaust leak, possibly a cracked manifold, or a leaky gasket; it doesn't need to be large to cause backfiring.

Kind of sounds like the baffling in the muffler has rotted out. That's what mine sounds like right now, time for a new one at least for me