2000 4.2 V6, 150K miles

I got a misfire on the way home from work the other morning that got progressively worse as the miles went by. Next day I scanned the codes and got P0300 (mult-cyl misfire) and P0302 (cyl 2 misfire). Cleared the codes and headed to the parts store for plugs and wires, it had been a long time since they were replaced. Cleared the codes, started the truck and same misfire but now P0302 (cyl 2 misfire) and P0171 (sytem too lean bank 1). Hmmm. Back to the parts store - I know my troubleshooting is a little lazy at this point - and picked up a coil pack. Installed it, cleared the codes and run. Same misfire. Compression checked all 6 cylinders. All 170+ so I'm calling the compression good.
...Stay with me!
Plugged the scanner in again and started playing around with the data streaming, truck running, O2 sensor - bank 1 sensor 2 showed 0 volts. Cool! Back to the parts store for an O2 sensor, installed and relieved. Started the truck, same problem same codes. 0 volts suspect B1S2 O2 sensor (bank 1 is the right side cyl 1,2,3). So I crawled under to look at the sensor connector (truck not running but ignition on) re-connected the sensor plug. and restarted the truck. Vrrrooom. Perfect. Scanner showed the suspect O2 sensor with good voltage now - same voltage as the other 3. Drove around, perfect. Turned the truck off and had a cool beverage to congratulate myself. Then just for kicks started the truck again....what the heck, misfire and codes back as before. No volts on the suspect sensor. Sooooo..hang in there..disconnected the battery for 10 min then reconnected, truck starts and runs no misfire. Disconnecting the battery for 10 mins does the trick. By the way the computer has never kicked out an O2 sensor code during all this. Pulled PCM out and checked wiring at connector and pins, stared at the PCM wondering. Before I pull the trigger on a PCM computer. What do you all say?
Help a newb out! thanks.

 

Welcome to the forum!

I deleted the other thread you started on this topic in the electrical section since duplicate threads on a single topic can lead to confusing responses that will waste your time.

Hope someone has some useful advice for you soon!

- Jack

 

Thanks. Thought this might be a better place to post the topic.

 

No worries! I don't really think the PCM has much of a history of going bad. I would not be in a hurry to replace it.

- Jack

 

Welcome to the forum.
Some body has to break the news that your very short on what's going on and what the data means.
First, you don't need 10 min. to reboot the PCM. One minute will do it.
Second, you cause the PCM to enter complete diagnostics all over again and it still finds the original troubles because they have not been fixed.
Third, the rear sensors are Cat monitors and normally do not very their output very much unless the cats ahead of it is getting bad.
Fourth, a faulty sensor will be detected because the PCM uses them for info input about Cat health.. If they don't work as expected the PCM can detect it.
Fifth, a 171 code will set a CEL lamp because one or both 'front' sensors detect too much Ox in the exhaust. It's not a sensor trouble.
We need to know what the codes are now, after the motor has been run long enough for detection of all codes to take place.
Do not power the system down or you lose this information.
Then we go after the causes of the codes and why they set..
Good luck.