Hi guys, I’m new to posting on this forum, but I’ve done a lot of reading on here that’s been helpful.

I have a 1997 Ranger, 4.0 Automatic Ext cab XLT. Just bought it. Third ranger that I own. It runs and drives, but idled rough upon cold start up. It had 2 codes stored. P0171 and P0174, lean code both banks. I have a scan tool that I connect to my phone, and I can watch numbers, temps voltages etc.

My current problem is, I am getting no voltage readings off of any of the oxygen sensors, other than 0.000vdc. And the fuel trims are all at -100%. So since studying my Haynes manual and reading about this exact topic on a thread on this forum that ended quite abruptly, I began doing the following.

I found the 15a fuse in the #3 position under the hood and it has 12v on both sides of the fuse. (KOEO) Im
not getting any O2 heater codes, so I should have assumed that this wasn’t the issue. But just for giggles, I moved down to the oxygen sensor connectors and checked for voltage down there as well. The lt blue/orange tracer has 12 volts at all 3 O2 sensors, and each ground wire for each heater circuit checked out to their respective pins on the PCM plug. To test those wires for breaks or shorts, I disconnected the battery, unplugged the PCM to avoid frying it should I have touched the wrong wire or something, and used a couple jumper wires, a half shot battery, and a test light to draw current through the wires to ensure that if one was almost broken, it wasn’t just hanging on by a strand.

Next, I did the same test with the sensor circuits. Same thing, both wires for each sensors circuits check out good, I then used a multimeter to check for shorts to the frame or motor if something burned or rubbed through. I confirmed my grounds were good with the test light/ jumper wire. All checked out good.

After all that, I don’t have any voltage readings from any of the O2 sensors other than 0.000vdc. I then willingly committed the unforgivable sin and threw 3 new O2 sensors at it, even though I knew it would be very unlikely that all 3 crapped out at the same time. I just didn’t know what else it could be at that point, but even after that I am STILL not getting any readings other than 0.000vdc on my scanner for any of the sensors. Could this be a bad PCM? Or could it be a PCM ground issue? I only saw two potential ground wires sticking out of the wiring harness about 6” away from the PCM itself that might have been a culprit, but I have no way of knowing if they are PCM grounds or not. I cleaned them up anyway. Or, is there something that the PCM is looking for that it needs before it will register those readings? (Like needing a crank sensor reading before firing the plugs) Any help on anything that I might have overlooked would be greatly appreciated. Thanks again in advance.

FF

 

So I figured it out. After checking all wire connections from the O2 sensors, and all the grounds coming off the computeR, I decided to throw a PCM at it, and 2 minutes after running it I had o2 sensor readings. Maybe not good readings cause there is still a problem with a rough idle, and a half- non functional egr valve, but at least the pcm is getting o2 sensor readings and doesn’t have the fuel trims at -100%. That makes me happy.