me too, worst thing is when a thread just ends and you never know what happened.
So if you ever have to change your CAT, here are a few things you should know. This is most easily done if you have a lift or hoist of some sort. We did it on jack stands. The biggest problem with that is getting the whole piece in there (if you go direct fit like i did). detatching and attaching are the easy part. The manual (thanks a millionth time mooseman) tells you to remove the transmission support bracket, and tbh i think it would have saved us some time. We detached it and then unhooked/lowered the front of the muffler and removed the small cross piece there. But there still wasn't enough room to jimmy things around. Ultimately we removed the bracket that the pipe goes into which involved loosening part of the transmission bracket anyways. So unless you have your vehicle way up in the air, just remove the transmission mount/support bracket as per the manual, imo.
fyi, cut open the old pipe where the CAT was, it was indeed mostly plugged at the front, so the initial/main power loss diagnosis was correct, bad CAT.
I reused the downstream o2 sensor because it came out easy. Ultimately that pesky upstream we broke off and removed with a 6 point socket (still with grief). Chased the threads carefully before the new one went in as it didn't come out great, but now it's all swapped out.
Now, we got everything back together and I fired it up. My mechanic said it sounded like there was still air escaping somewhere, so he brought out a tube to listen through to pinpoint. It wasn't coming from anything we changed as far as he could tell, but he thinks he narrowed it down to up in the manifold under the heat shield. He told me to drive it for a couple of days (first to make sure my power is back), then suggested I take the heat shield off and look at the manifold. He believes I could have a crack in it somewhere. Told me that if the sound goes away when it heats up that's likely what it is as a crack will be more open when cooled but expand together when it's hot. He said what is possible is that it will push exhaust through the crack but also allow oxygen in, tricking the o2 sensor and causing it to dump more fuel. This makes sense as one possibility to me. Hopefully this weekend I can get the heat shield off to inspect.
My coolant temp has been way more stable since the change. Once I'm up to temp I hover between 198-206.6, usually around 202. This is a combination of in city and highway speeds, seems like I'm cooling properly. Regardless I might still change the thermostat. I also think I might change the plugs again. I did in the winter but I didn't use the delco's, and after reading and reading and reading on here I see I've comitted a serious no-no. I will also clean the throttle body again.
I've been monitoring some things. My short term fuel trims are scary out to lunch, all over the place, and even the long term trims are constantly -%, even pushing over -8 or -9% sometimes. Somehow I did not set up my O2 logging properly, but watching it live my downstream o2 sensor voltage settled out to around .7 (700 mV i believe?) and the upstream is jumping around as expected. That seems high for the downstream though, no? Should be closer to 400 (.4)?
Googling fuel trims it seems as though my excessive correction to the negative could indicate a leak in the manifold (among countless other things). as per
http://www.easterncatalytic.com/education/tech-tips/fuel-trim-can-be-a-valuable-diagnostic-tool/ :
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing.
The upstream o2 sensor is new, so I'll rule that out for now. I have no MAF as previously established. So as far as things I can easily check/fix I will change the fuel filter and t-stat and inspect my manifold. Still seem to be on the right track?
btw I can post some data logs in csv if anyone's interested in seeing what I'm seeing.
Should I start a new thread I wonder since I have no more power choking?
