I've been battling an engine power issue for about 4 months. Slowly swapping things as budget allows. As my profile reads, I have a 4L, on 35s, with 4.56 gears. I used to be able to maintain 5th on the highway, and even pass in 5th. Now I can barely maintain 5th on an even grade. I can flog it all I want, there is no dead spots,
I've replaced MAP, IAC, TPS. Tested fuel pressure at the rail. Everything is good. Compression test came back dead on, on all 6 cylinders. Cleaned the intake. I have run seafoam through fuel system, through crank case, flogged, then did an oil change and new plugs.
All that is really left is the o2 sensors (downstream was replaced last winter- SG1815 O2 Sensor
is the model I replaced it with), and the coolant temp sensor.
So I loaded up my trusty Torque App, and my OBDII Bluetooth reader and read the voltages on the o2 sensors while driving. My upstream fluctuated from .1 to .3 and the downstream stayed at 1 at all times. Does this indicate my downstream is bad? Or could there be an underlying issue (bad cat? plugged cat?)? Muffler is brand new. Very little to no soot on tail pipe as well.
As for the coolant temp sensor, can I just unplug it to see if everything gets better? Or does the previous o2 info, pretty much point to that?
Thanks for the help!