I am really starting to wonder after my towing tonight if what I thought was metal heat shields rattling, that I am really having my engine backfire when I downshift and let off the gas pedal. ANY, and I mean ANY guesses are welcome.

The noise happens at no other times other than higher RPMs and release of the gas pedal.

 

Are you sure it is backfiring? I have the same thing happen when I engine brake at higher RPM's. It is Back pressure. It is safe. More distinguishable with louder exhaust systems. And the heat shield rattling may be pinging, caused by pre detention. Try replacing the spark plugs for a step colder than stock. Autolites 3923's are the best and are cheep. You can also try colder thermostat. Or a higher Octane rated fuel.

 

Not sure it is backfiring. Could be back pressure. Would be nice if that is what it was.

If it is back pressure I bet I have no rattling heat shields, it may all be the same problem because I am currently running the Autolite 3923s, a 180 degree thermostat, and the V6 PCM with premium gas. Also when I went into do the head gasket I changed the plenum. This has been the case with the truck for a while but I noticed it more towing today.

 

+1!! I have a flowmaster 40 and no cat, when I engine brake (which is all the time now with the manual transmission) you can hear the exhuast go "POP....POP.... POP.... POP" Personally, I love that sound, but I have gotten some interesting looks from people, especially around school. :P

But Crazy is right, its just high backpressure since the engine is turning over faster than amount of gas being burned would normally allow it to turn over.

 

When I let off when it's cold or downshift just right I can make mine do some crazy popping, it's normal. I think exhaust leaks can also cause excessive popping, might want to take a peak.

 

All of you are right. I tried it again today and it has to be back pressure.

 

hey guys, im back!

it sux being poor, lost the internet for a bit. but anyway, my truck does the same thing, and i was wondering this also, so its completely normal with our trucks? cuz ive never heard a ford or chevy do it.. is it maybe just a timing issue that dodge couldnt solve? i really dont like the noise personally. everyone looks at me like its a peice of crap, which its the complete opposite of..

 

Does it sound like the popping in this video of the Old 2.9 in my Bronco II? It popped until the injectors shut down (as heard towards the end of the video), my 4.0 does it a little bit but the injectors shut down much quicker than the 2.9 did when engine braking.
http://www.youtube.com/watch?v=KYjD6...eature=related

 

you have a bronco II too! im still in the process of convincing my old man to hand down his. he has an 84 bronco II eddie bauer edition with a carbed 2.8 and 4 spd with od. the brakes are shot on it and its almost a box of rust... but now that i think about it, i heard that, just never thought anything of it. i know the chevy 350 doesnt pop like that, my buddys got one with some really cheap mufflers on, no cat, 3' piping and it doesnt do it what so ever. but i also know the 360 does it, but im not sure about the 318... im sure if you get the right muffler, you could make it sound nice and loose the popping sound? maybe thats all it is? or maybe smaller piping to increase backpressure?

 

+2 lol

i would have to say thats my second favorite sound my truck makes (the first being right around 5k rpm... screaming v8)