First off i would like to say Hello as i am new to this forum.

I have a 92 Dakota 2wd ext cab with the 318 MPI motor. I believe my o2 sensor is bad and wish to replace it. As far as i can tell this motor only has 1 o2 sensor which is located in the Y pipe just upstream from the cat. My problem is, there are 2 different length pig tails listed at the auto parts store and i cant find where the connector plugs into the wiring harness. It looks like is it on top of the transmission. I did find another connector that looks like it might be the o2 sensor plug comming out of the harness near the passenger side firewall.

I guess what i am asking is: What is the easiest way to change this O2 sensor? And why is there 2 different length pigtails listed for the same application? (18" and 34" approx.)



Any help would be greatly appreciated!

 

Well, I do believe you have an upstream and downstream sensors.
My book shows that, as you said, the upstream sensor is located just aft of the Y-pipe, on the side of the transmission (sticking out straight up I believe).
My book also shows that the downstream sensor is located not too far from the rear of the cataytic convertor (sticking out kinda to the passenger side).
Apparently, the upstream sensors connector goes over the transmission, while the downstream sensors connector is on the right on the frame.

As far as the length, I do not know. The connector by the transmission will be the correct one. The one you said was located near the passenger side firewall is for the oxygen sensors, but, it is the 'master connector" if you will, and the wires splice off after that to the appropriate sensor.
I haven't taken one off, I have attempted to on the Civic I used to own ([:'(]) but I never was able to get it off. I've heard that spraying some WD-40 or-similar stuff on it, and letting it settle in, and than using an actual oxygen sensor socket makes it a lot easier.
Let us know how it goes.
BTW, whats leading you to believe your oxygen sensor is bad?

 

The sensor in the Y pipe has a pigtail that leads up over the transmission and it is impossible to even get my hand up there to feel the connector. All the OEM replacements show a connector at the end of the pigtail from the sensor. I looked for a down stream sensor directly after and on the cat and didnt see one. I will look again though. None of the sensors i have found specify up or down stream.

A friend who is a NASE certified mechanic checked the "check engine" flashing codes and told me it was the code for O2 sensor but i forgot to ask the number of the code.

The motor starts up easily then in under a minute the "check engine" light comes on. Idle is rough and the engine feels like it is loading up and my gas mileage has dropped by 4+mpg. You can feel a significant loss of power at normal highway cruising speeds and under hard throttle. The check engine light will come on right after starting if i touch the gas petal and raise the rpms.

The motor has a new PCM, plugs, wires, cap and rotor with about 140,000 miles and ran fine till a few days ago when the "check engine" light came on. All fluilds are within spec too and the gauges show good temp and oil pressure. The fuel filter is about 2 years old so i will change that the next day it isnt raining. I have also checked to make sure the coil and plug wires are secure. Idle control solenoid has also been removed and cleaned. Ive even checked to make sure the throttle body is secure and used ether to check for vacum leaks.


If its not the O2 sensor im stumped, i know it has not been changed in over 60,000 miles.

 

Yea, it probably wouldn't be too fun to get to that connector.
The pictures in the book I have kind of disagree on the exact location of the down stream sensor. One picture makes it look like its pretty much just after the cat. while another makes it look like its a little down stream (maybe a foot, foot and a half) from the cat.

Let us know how replacing the O2 sensor goes, and if that solves your problem.

 

I just changed my o2 sensor a short while ago. It is possible to get to the connector. Just follow the wire comming up out of it. Kind of tug on it a lil bit and you can see where it goes on the other side of the tranny. I managed to guide the plug up and over the tranny with my hands. Granted I have a manual transmission, those of you with the auto may not be able to do this. You will need a 7/8 wrench I believe and sometimes they are a real bugger to get out of the bung in the pipe. Mine came right out.

I bought the one with the 18" lead and had plenty of wire to get it back to the plug location. Also the plug is on a hanger. If you slide it one way or another you can pop it off this hanger and wrangle it to a more accessable location. I also doubt you have a downstream sensor. Prolly just the single one like the rest of us with the pre-95 dakota.

Hope this helps.

 

Thank you both

And i will let you know how it turns out

 

Well, my buddy brought over his Snapon analyzer. The O2 sensor is fine.

The analyzer gave a cylinder#2 injector error. The plug on the injector was not seated and almost fell off when he touched the wire.

Problem is solved but he suggested replacing the injector if the problem happens again.

Thank you for hosting this board and the information is supplies.