Hi everyone i am new to the forum and appreciate all help in advance. I have owned my 2004 zr2 2 door blazer for several years now. Bought it for $1200 with only 65,000 original miles. It now has 185,000 miles and it’s started to give me trouble. Had the trans rebuilt 20k ago and it’s already toast again. That’s a separate issue but main issue I’m having is it runs pretty rough at the moment. It idles fine but when you try to give it gas especially after warm up it pops and runs like crap. Sometimes I can put my foot to the floor and it will still only turn maybe 3000 rpm. I have already replaced the catalytic converter a couple years back. I am currently getting cat codes as well as one for the MAF. I replaced the MAF and still runs like crap. I’m thinking my cat is clogged again but is there any way to know for sure? Also I ran the truck for about 1 minute and then touched the exhaust. The resonator (I think is what it is) towards the beginning of the exhaust just after it collects is super hot. Exiting it though into the cat is significantly cooler to the touch.is it possible the resonator is clogged? I’ve had trouble with my truck overheating too as well as extremely poor fuel economy. It gets roughly 9 mpg on the expressway. Any tips on what to check first would be greatly appreciated

 

You said it's running rough and and you got low mpg. My first thought is that spider fuel injector these trucks. Those things stay going bad, I'm on my 3rd one, in my 6 years of owning my jimmy. Check to see if it's that.

 

The definitive test for excessive back pressure is a guage in one of the O2 sensor ports to measure. A quick and dirty test is to remove an O2 sensor physically and see if it runs better. There are two ways a cat can fail. First is it stops cat'in and in that case the rear O2 sensor starts switching like the front sensors instead of flat lining between 0.5-0.7 volts. The second is it starts to fail physically and plugs up with catalyst debri, It can be one, the other or both. There are other tests like vacuum behavior, IR guns, live data etc but the first two are definitive.

I would confirm no excessive back pressure and then we can start analyzing your problem. We would start with a fuel pressure leak down test and any codes and then go from there.

George