backfires hissing sound

please help someone 97 dodge ram 5.2 engine runs great when first stated after warm up it starts making a hissing sound very loud hit the gas a few times and it goes away,but running rough ,drive out onto the highway and starts to backfire ,move the gas up and down a few times and it will take off, "backfires thur intake"

You may have a clogged catalytic converter. Do you have a rattle in your cats, or reduced exhaust flow? When it's making the hissing noise does it not have any power at high rpms? These are all symptoms of needing new catalytic converter(s), and there are numerous posts here about it.

You may have a clogged catalytic converter. Do you have a rattle in your cats, or reduced exhaust flow? When it's making the hissing noise does it not have any power at high rpms? These are all symptoms of needing new catalytic converter(s), and there are numerous posts here about it.
i replaced the cat already, and the computer also,"it would not let u access info with the scanner", but it has not set any codes, the power is fine once you get it to take off,the sound is it letting air in somewhere, IAC , i guess . it is a really weird problem , it does not have a intake gasket leaking or it would leak all the time,but if it keeps backfiring thur intake, it will!! i kind of wonder if the fuel pressure could be low enough to cause it , but if you just floor it , it will take off fine, the harder you drive it better it runs.

With the hissing I'd think a vacuum leak or intake leak, but you said you've already checked the intake.

Could it be some sensor is giving wrong indications?

Have to admit I'm stumped.

you must check you o2 sensor it won't make the hissing sound but could cause your drive issue as the pcm ignores the o2 input at wide open throttle but plays a big roll in all other throttle positions

you must check you o2 sensor it won't make the hissing sound but could cause your drive issue as the pcm ignores the o2 input at wide open throttle but plays a big roll in all other throttle positions


the o2 may be possible ,i have wondered if the engine could be running so lean that its starts popping back, the hissing sound is the IAC ,but i am sure it is not the problem either b/c u can unplug it and still runs the same "stops the sound" .
also i wonder if the fuel pump could be dropping pressure to low sometimes, and making the engine go lean- i checked pressure by taking fuel line off at rails - but engine was not running,"not the way for sure" how would you check! also thanks for helps guys, i always do my own work, dont want let some shop lose on my truck!

i would remove and clean your o2 sensors, and IAC for that matter. sounds like a similar problem i had about a year ago, turned out to be the o2 sensors

I had a problem similair with a 200 ram 5,2. the truck would have a loud air sound and would missfire. It would clear up after a few minutes. It turned out to be the o2 sensor sticking that caused this problem. No codes were thrown.

faulty egr valve will also cause backfire...

You may have a clogged catalytic converter. Do you have a rattle in your cats, or reduced exhaust flow? When it's making the hissing noise does it not have any power at high rpms? These are all symptoms of needing new catalytic converter(s), and there are numerous posts here about it.


I AM INCLINED TO AGREE WITH FRED.VACUM LEAK..WILL CAUSE THIS PROBLEM.IT WILL CAUSE A HISS AND A BACKFIRE
FRED SEEMS TO KNOW A LOT ABOUT WHAT HE HAS TALKED ABOUT.
WITH ENGINE HOT AND AT IDLE TAKE A PROPNE TORCH TURN GAS ON LOW ---DO NOT LIGHT---- AND SPRAY THE GAS AT ANY AND ALL VAC.LINES GASKETS ECT... IF THE EINGE SPEEDS UP WHEN SPRAYING A CERTAIN AREA FIND OUT WHAT IS PULLING THE PROPANE INTO THE ENGINE AND FIX IT
DAVE