Hey guys and gals, just replaced my Chebby with a 96 3/4 ton 2wd, always wanted one of these since this bodystyle came out. The downside is I am chasing a problem and I am not having such good luck. Automotively speaking, my area of expertise is more relegated to 1949-51 Mercurys, so to say I'm out of my field is an understatement.

Now, in short, here is the deal. I bought this thing a few weeks ago and upon startup, the check engine light was on and it ran awfully. Muffler was put on backwards, I cut it off and straight piped it (temporarily), next got it scanned and it gave me the following. P0171 P0172 P0141 and P0138. So...I tinkered a bit and pulled the connectors on upstream (cat) 02 harness, drove it...nothing, then downstream 02 (post cat) and it cleared up a lot. Awesome, so I replace downstream 02 and spark plugs while Im at it. First drive was OK, a little stumbly after startup, but an hour highway trip fine. Stop for gas, get back on the highway and it runs like poo again. Finally just threw a light again but I can't get out of here for scanning till later, maybe you guys have an idea?

In short what it does now is after startup (even when at operating temp) it stumbles for a minute or two. It gets *better*, then on the driving it misses and stumbles until around 13mph, then straightens right out. When slowing down again, or at a light, it stumbles like CRAZY and pretty much at all points the truck is running rich.

I think you guys in advance for any insight you might shed!

 

hmmm I know spark plug routing will be mentioned theres a TSB around here somewhere. Maybe a clogged cat not sure how they really act

 

Hmm...the more Im reading the more I am wondering if I replaced the wrong sensor? Does the front sensor (in the cat, or riiiight before it) manage fuel/air mixture? Does the second (after cat) just monitor how the cat is working? I mean I pulled that o2 and it was absolute toast, so if I replaced the wrong one I wouldn't think that I did it for nothing, but I'm wondering if my culprit is the front 02?

 

Yeah that's the way I have read it works. Never hurts to change it and find out. They are suppose to be replaced every so often anyway

 

Alrite, the more I think and read about this online, it seems I just plum replaced the wrong o2. I mean the one I replaced was wiped out looking but I think my running rich and throwing o2 codes is the 1st sensor. Just wanna bump this to see if anyone is on board with my train of thought before I enter my credit card info and buy this sucker. Is this how it works? The 1st sensor determines air/fuel mix for the engine and the 2nd sensor just monitors the work of the cat itself? Thanks folks!

 

The first (upstream) O2 sensor monitors A/F mixture and the second (downstream) O2 sensor
only checks if the cat is functioning properly. (everything else that was written after was wrong
so i deleted it)

 

Lol, are you serious? I can do that? Some of the catalogs listed them seperately, I had no idea I could even do that. Thanks man, Im going to do that as soon as I can.

 

check your TPS while the truck is running unplug it, if it stumbles and wants to die the sensor is ok, if it does nothing te sensor is bad

 

Ya know, i think i may have misinformed you ..... man its been a while since i've contributed
and i have forgotten things. Sorry man, i feel like a dumbass.

 

No sweat, Im going to try it anyhow, they are listed seperately but some are universal up or down stream, so the way I see it, it cant get worse! Or, well, maybe it can...