I have a 98 GMC Jimmy SLS. Right now it's persistently popping P0174 (bank 2 system lean) and P1153 (heated oxygen sensor bank 2 sensor 1 insufficient activity)

I have replaced all the vacuum lines I could find with signs of dry rot. I have replaced both O2 sensors on the Y pipe. I have replaced the MAF sensor. I'm out of ideas.

It's pulling about 10-12 MPG right now.

any suggestions?

 

I'm really stumped guys.

It is still popping codes P0174 (bank 2 system lean) and P1153 (Insufficient activity heated oxygen sensor bank 2 sensor 1).

We performed a smoke test, there was a leak where the intake hose met the throttle body, we sealed that gasket and it is not leaking anymore. I have also replaced all three O2 sensors, the Mass Air Flow sensor and a number of vacuum hoses that I found were dry rotted.

We did the smoke test again, this time through the brake booster hose. We left it going for five minutes and the only smoke that became visible was when it traveled all the way through the system and out of the intake for the airbox.

The brake booster tested good.

I also discovered that sometimes the exhaust will spit out black/brown specs and that there is an accumulation on the curb behind where my exhaust pipe exits. After I replaced the 3rd O2 sensor (downstream behind the cat) it stopped spitting out the flecks and I haven't observed them since.

It still pops the codes every time I clear the codes.

I'm completely out of ideas again and so is my uncle. Does anyone have tips or ideas of what to do next?