O2 Sensor Install

[snakedoc67]

Trying to install a new O2 sensor but can't get the new one to start into the manifold. Was wondering if anyone had any tips or suggestions. The old sensor doesnt show any signs that the threads in the manifold are stripped. 

 

[Garvin]

Make sure you take a real close look at where the thread ends on the manifold (where the O2 sensor starts to thread into) as I've seen many threads that look good yet they were screwed up just enough at the end where it wouldn't catch the sensors threads.  If both the sensor and manifolds threads are good then it should go in when you get the correct angle.  Auto parts stores (atleast the ones around me) do sell an O2 sensor thread chaser to clean up the threads in the manifold.

[HOrnbrod]

A common spark plug thread chaser like below (w. 14mm & 18mm threads) works just fine on Jeep O2 sensor M18 threads. You can get one at Autozone or similar for about $7. Don't forget to use a little anti-seize on your new sensor threads.

[snakedoc67]

thanks, will run out and get the chaser

[robbie95]

hey, just wanted to ask.. how did you know your o2 sensor was bad? I think mine is bad but how can you tell for sure? I have been getting bad mpg, exhaust is stinking up the joint, running kind of funny (not bad but it could be better) would appreciate it if you told me. maintenance req light is on too..

[snakedoc67]

hey, just wanted to ask.. how did you know your o2 sensor was bad? I think mine is bad but how can you tell for sure? I have been getting bad mpg, exhaust is stinking up the joint, running kind of funny (not bad but it could be better) would appreciate it if you told me. maintenance req light is on too..

About the only way I had any idea was from reading thru the forums here and seeing what the advice was given to the other people with the same issues. My gas mileage had dropped to around 6mpg, the truck would backfire occassionally and would bog down when driving. After replacing the O2 and fuel filter today its back up to 10mpg. Still not the 17 it was when I got it, but better. I also put some Seafoam in the fuel to see if that helped with cleaning the injectors any. 

[cruiser54]

They're supposed to be replaced every 82,000 miles or so anyway.

 

O2 sensor testing

1987-1990 Renix

For the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immedietly after start up. Loss of that power will hurt gas mileage even with a good O2 sensor.

One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor.

The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground.

At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing.

If the O2 sensor readings are not right, say they read 4 volts or 1 volt steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 volts on the orange wire, and 5 volts on one of the two black wires), and ensure the ground wire (power off) reads less than 1 ohm to the battery negative post.

A leaky exhaust system or leaky fuel injector(s), or bad compression, bad rings or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.

 

[snakedoc67]

The O2 sensor change did not help as much as i was thinking it did. I am still getting power losses as I am driving, usually when I'm shifting between first and second or second and third, or even as I'm driving down the street. I will press down on the gas and have no power available. A few times it has backfired after I shut the engine off. I can smell fuel inside the cab and I'm wondering if this sounds like a bad injector. The last four or five days the first start in the morning requires me to pump the gas as I'm cranking the starter over and continuing until it catches. While running it idles between 900-1000. I am planning on doing the sensor ground refresh in a few days when I have time available. 

[Stacks]

Your symptoms sound like a plugged or partially plugged catalytic converter.  Especially if all else checks out OK.

[cruiser54]

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION

Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

[snakedoc67]

CRUISER’S VACUUM TEST FOR EXHAUST RESTRICTION

Your vacuum gauge should come with an instruction booklet outlining the procedure. Hook the vacuum gauge up to a source on the intake manifold. Start the engine and note the vacuum reading. Usually 17 to 21 inches of vacuum. Throttle the engine up to 2,000 to 2,500 RPM for 20 seconds or so and the vacuum reading should stabilize to the same reading you got at idle. Let the throttle snap shut. The vacuum reading should shoot up about 5 inches of vacuum higher for a second and then come quickly down to the original reading. If the vacuum reading stays high and comes down slowly with jerky needle movements, you have an exhaust restriction.

Thanks for the test procedure Cruiser.  if I do have a plugged cat. conv. can i get away with replacing it with a piece of straight pipe (no emissions testing here,  :banana: ) or  does something like the ECU get a reading from it? 

[cruiser54]

Discussing removal of federally mandated emissions equipment is not allowed on the forum.

[snakedoc67]

Naturally, I would not promote a direct violation of federal and state laws, the question was more to find out if a failed cat. conv is tied into other systems such as the ecu or other sensor getting a reading from it and if it needed replacement immediately or if a temporary fix would work. My show of happiness at not having emissions testing in this state is more from my tend towards older vehicles, such as my 58 Edsel that probably would never be allowed in California if it ran but I do remember when we did have to take the cars in when I was a kid. lol 

[HOrnbrod]

There is no signal generated to the ECU or anywhere else from the exhaust system except by the O2 sensor.

 

A "test" pipe is legal for troubleshooting problems in most all states, even with those with emission regs for our plus 20 year old year vehicles. Some states require the pipe be installed by a state certified shop for a limited time frame. Since you are not in one of those states, suggest you do it yourself "for testing purposes only". Like the below:

 

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[snakedoc67]

how much of a possiblity is there that this would be a cause of poor mileage (6-10mpg). 

[HOrnbrod]

If you had a clogged cat, it would show up first by running hot, especially going up long grades.

[snakedoc67]

Not very many grades around here, but for months now its barely been reaching the low range mark. 

[cruiser54]

Ever do the ground refreshing and other stuff in my link below?

 

C101 cleaning

 

Connector and relay /receptacle refreshing

 

Check sensor grounds

 

Intake manifold bolts loosened up?

 

Vacuum line from throttle body to MAP sensor have a small crack?

[snakedoc67]

i started working on those as time permits. So far have completed refreshing the grounds on the block and about halfway thru cleaning out the C101 when i had to focus on other projects right now.