Sorry for starting so many threads. I think this is my last issue for a while.

The truck basically doesn't have an exhaust. Everything is good enough from the engine to the first 02 sensor. The cat converter and second 02 sensor are gone. I purchased a new 02 sensor, the 'downstream one. Was hoping I could plug it in and just zip tie it somewhere down there. I'm obviously not an exhaust expert.

That doesn't work because you get p0171, too lean. That makes my engine run rough to accommodate, is that right? Or is the only issue that its giving me the check engine light.

the right thing to do is get a new exhaust. That will happen eventually.

In the meantime, is there some sort of delete I can do to trick the computer. Better yet could I just limit the oxygen flow to the sensor or somehow otherwise fool it?

Thanks

 

P0171 is caused by the *upstream* sensor. The fact that you got the code after adding the missing sensor makes me wonder if ******** that worked on it before switched the O2 sensors and you've been running without a working upstream sensor which would explain the bad MPG you mentioned in another thread.

Two options for diagnosis:
- If you have a scan tool with live data look at the readings for the two O2 sensors. If sensor 1 is lean and sensor 2 is rich they are swapped. You probably also have the fuel trims maxed out.

- Going by the 96 wiring diagram which I think is the same in 97, the four wires at the O2 connectors have one wire that is different between the two sensors: tan/white is upstream and orange/black is downstream.

 

Once you get that upstream figured out you need to have the downstream in place. Chances are you will not get a code with the cat out, if you do just get a code for catalytic converter just get a spark plug de-fouler for the downstream sensor, that has worked on my last 2 5.9l's and 3 3.8l's that got the cat's removed.

 

Both sensors, front and back have black white and grey wiring. 2 white wires.

So potentially I have a downstream sensor as my upstream sensor as you were saying. If the wiring is always color coded.

A new clue has arrissen. I drove the truck for 5 miles. The exhaust was warm, but the 02 sensor was red hot. Its not touching anything, so I'm thinking the wiring is doing that... thoughts?

 

I left the plastic on it originally thinking that would help protect it since its not doing its intended job anyways.

I have exhaust leaks from manifold to sensors. Big leaks. So I suppose that is the whole problem? Now that my back sensor is at least plugged in, the upstream sensor is the one throwing the code? So I have to fix the leak probably

Or is there a way to fool these dumb things into thinking all is well

 

You don't wanna "fool" that upstream O2 sensor. It's the one that determines your mixture via the pulse width of the fuel injectors. No O2 sensor, no go juice for the engine...WELL, other than the default "rich" setting that HAL will give ya to gecha home.

 

The downstream O2 seems to be nebulous on these '96 models. I've not had a cat with guts for years now n my downstream O2 doesn't see the need to let HAL know about it. I've got no anti-foul bung added to my downstream O2 sensor, the fuel trims are just fine (long n short both oscillate, but essentially both around +/- 2-3% during cruise) n no money lite. I think most guys will tell ya that the downstream O2 is meaningless to HAL in the '96's, bucha gotta have 'em in the exhaust stream to keep HAL happy.

 

Sorry I didn't describe that well I guess. You need to look at the wiring harness side not the wiring from the sensor to the connector.

 

All very useful information guys. Thank you.

I am pretty convinced the leaks in the exhaust are causing the problem. Just spent a morning with the caulk gun/ permatex Red. Hoping for the best. Resetting computer now and going for a test drive.

 

Feels like a new truck. I didn't realize how fouled up things are when the 02 sensors aren't happy. Back one is still just hanging but front one doesn't have a massive air leak coming in anymore

Appreciate everyone's help immensely