When im pulling my boat and the engine is around 2600-3000 rpm the engine will backfire and pop. It only happens under a load. it also seems like it is coming from the cat or from the throttle body, it definetly isnt coming from the end of the exhaust. thanks for any help.

The Truck is a 2001 2500 5.9V8 with 100000 allready fixed the plenum.

 

Is your cat glowing while this is going on? Sounds like a restriction issue use a 1-6 psi pressure gage a pull the front O2 sensor out and insert a fitting on the hole and hook gage to fitting give your self enough hose to be able to read the gage from inside the cab. Take the truck on a short test drive and see how much back pressure the cat has If it is more than 1 pound it needs replaced!!! Next to dubble check your gage leave the O2 sensor out and go for another short test drive it it runs better and don't pop and back fire the cat it pluged. Befor you replace you cat and go to driving it agin check to see if it is running lean if so THIS IS WHAT CUZED YOU PROBLUM TO START WITH!!! EXTREAM TEMP. CAN MELT DOWN A CAT!!! IT SHOULD RUN AROUND 600DEGREES TO 650 DEGREES FARENHIT.

I hope this helps you out.

 

so how would i figure out if my truck is running lean? also it looks like there are 3 diff cats. 1 on each downpipe and then one right after the Y. is this right? or is one of these something else?

 

downpipe? you mean your Y pipe, you should only have one cat after the Y pipe

 

yea theres one after the Y pipe but it also looks like theres one right at the end of manifold before the Y. they each have a o2 sensor before and after them and theres no o2's before or after the one after the Y pipe

 

resonator?, but that shouldnt have sensors

 

ok so the one after the Y is a resonator? and the ones after the manifolds are the cats cause those have the sensors

 

when you go to replace it if it looks like it melted down it is due to extream lean runing and this issue will need to be fixed befor it melts down the new cat.