94 4.0 ohv 136 lean code bank 2

[leodk27]

Hello everyone

I have a 1994 4.0 ohv ranger with a 5 speed and 4x4

Recently it has been running lean on the bank 2 cylinders, I replaced the spark plugs, fuel filter, o2 sensors and pcv valve.

I’ve also checked for vacuum leaks and the vacuum of the truck which reads about 20 in/hg at idle.

Most I can get is about 60 mph of the highway and it’s getting annoying.

thank you in advance!

 

[RonD]

Welcome to TRS

If an engine is actually running Lean it will ping/knock when accelerating
Do you hear that?

I have the same vehicle, 1994 4.0l 4x4 manual trans

Only had lean and rich codes at the same time when shop that did the clutch reversed the O2 sensor plugs, but had BOTH codes at the same time, lol

136 (R) Oxygen sensor not switching/system lean Left or Front HO2S – Fuel control

Not switching can mean a bad wire

O2 sensors generate their own voltage by a chemical reaction to oxygen in the exhaust
0.1volt is Lean
0.9volt is Rich

Computer changes the open time on injectors while engine is running and this cause the voltage coming from the O2s to go up and down, that means the voltage is "switching"/changing as computer fine tunes air/fuel mix

So a bad wire would be..............0.0v so Lean all the time and not switching

O2s have 4 wires, 12volt and ground for the internal Heater, O2s must be above 650degF to work, so have a heater
Other 2 wires are a computer ground wire and the "signal" wire, the one with 0.1v to 0.9v

Check the wires on that 4 wire connector

O2 #1 is passenger side, #2 is Drivers side, Left side, the one with the problem

3 of the wires are the same on each
12v and ground, light blue/orange(12v) and black/white(gnd)
You can test these two wires with volt meter, 12v key on

The Orange wire is computer ground, reference ground, its connected to the Grey/Red wires you will find at ALL other sensors
You can ohm test this wire to any other sensor's grey/red wire, 0 ohms means its connected

The Red/Black wire on #2 O2 is harder to test, need to pull off the computers 60 pin connector
But just give it a good look see if has been chaffed or corroded, we are dealing with very low voltage, under 1volt so any problem with this one wire means 0volts and no switching

 

[leodk27]

Ok so,

I am getting about 3-8 ohms of resistance from the black wire to the pin on the connector going into the computer

I’m not getting anything from black red to the corresponding pin on the Computer connector

This confuses me because I get continuity and resistance at the computer connector I stated above but I can’t get voltage. Although I do get voltage across the orange and red/black wires, so the sensor is doing something.

The heater is definitely working getting 12v and ground no problem

 

[RonD]

There is no "black" wire, there is a black/white wire and its the ground for O2 heater, so yes low ohms, 3-8 is fine

The RED/black wire should be 0 ohms to pin 39 on computer connector, direct connection, so thats the problem, broken wire

 

[leodk27]

I meant black/red wire, the one that should be 0 ohms, but I will run a new wire thanks!