# Stuck O2 Sensor, 89 2.4 Running Rich



## Smith1000 (Dec 29, 2005)

The O2 sensor wire was touching the exhaust pipe and it partially burned the wire. The insulation is burned off a section of the wire. I had some of the wiring loose when recently replacing the head gasket. It started running rich and I believe this is probably the culprit. I replaced the bad section of wire, but it didn't really help it much. It will idle fine, but will puff black smoke on acceleration. After shutting it down, an immediate restart results in a stall and quite a bit of black smoke. It will then clear and run okay, but it's still running rich.

I can't seem to get the old O2 sensor off. It is stuck extremely tight. Tried removing it hot, but no go. Does anyone know of a sure fire way to remove a stuck O2 sensor? 

I am thinking I may have to drop the exhaust pipe out in order to remove it. I broke the handle off of a small pipe wrench turning on it. Has anyone run into this situation before? Thanks.


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## Smith1000 (Dec 29, 2005)

I am thinking it may be easier to drill a new hole for the O2 sensor and weld on a nut to install a new sensor in a different spot that is easier to access. Does it matter if the O2 sensor is located closer to the cat converter? I could do this without dropping out the pipe.

Does the catalytic converter affect the operation of the O2 sensor?


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## dvdswanson (Nov 6, 2005)

use penatrating oil, then try to remove it. remember to clean it off before starting back up, it is flamable.


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## Fred S (Aug 26, 2006)

Smith, you're on the right track with welding on a new bung. Even if you got the old sensor unscrewed, the threads in your exhaust are more than likely ruined.

It's a pretty simply job to replace the bung if you have a welder and a mild amount of skill.
If you lack either of the above, it's an even simpler job provided that you have a credit card. Any muffler shop can do this job for you. Been there, done that.

For the sake of reducing exhaust restrictions, have them cut the old sensor out and put the new fitting in the same location.

If you're doing it yourself and need a new bung, go to an auto parts store and get an 18mm spark plug anti fouler, and cut it up. The internal thread should match your O2 sensor perfectly.

Fred


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## Smith1000 (Dec 29, 2005)

Thanks for the advice. I think I will try to soak the sensor in penatrating oil before going further on cutting it out. Maybe it will break free.

In checking the stuck O2 sensor tonight, it does seem to be putting out some voltage. Here's what the truck is doing. If I run the truck hot and shut it off and then start it about 3 minutes later, it initially starts and idles normal only briefly (seconds). It then cuts out (idles down low) and will sometimes die/stall. If I pump the gas, it will keep it running and really put out the black smoke until it clears (the excess fuel). It will then idle evenly and run. If I stop and reve the engine, it will put out black puffs of smoke. Cold starts-no problem. It fires up clear and will warm up normally. Does this sound (generally) like what a bad 02 sensor will produce?

Had the head off recently to replace the head gasket. The valves were done also. I think maybe I should set the valves hot and also, possibly look for a vacuum leak or intake manifold leak? It seems like it is loading with fuel when it is shut down. I am not convinced the way it is acting is all related to the O2 sensor, but maybe it is. It will run good, smooth and quiet. Does it seem like the way it is running could be for another reason besides the O2 sensor? 

Kind of grabbing at ideas here. The valves were cold set in the machine shop. He said to run it about 500 hours and then adjust them. He thought they would be okay. I wonder if there are any critical ground wires for the TBFI system that I should check?


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## Smith1000 (Dec 29, 2005)

I cleaned the MAF sensor with MAF spray cleaner and then replaced the pcv valve. Neither of these changed the situation. Guess I'll have to replace the O2 sensor on Saturday. The injector is really clicking. I can see gas spraying down on the valve in the throat. If the O2 sensor doesn't fix it, I guess I'll have to do some more analyzing. There do not seem to be any vacuum or intake manifold leaks.


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## smj999smj (Jan 1, 2006)

When you repaired the O2 sensor wire, did you make sure to seperate the shielding away from the signal wire? There's actually two circuits in the single 'wire" to the O2 sensor. A braided, very fine wire shield is a ground to the ECM to prevent electronic interferance to the O2 signal wire, which is the core of the wire. If these two circuits are seperated during the repair, the O2 signal wire will be shorted to the ground "shield."


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## Smith1000 (Dec 29, 2005)

The wire to the sensor had been spliced previously (previous owner) and a regular piece of automotive electrical wire was running to the O2 sensor. This segment of wire ran to the wire that goes to the ECM (to a black wire). It doesn't appear to be shielded. The new Bosch sensor does not appear to have a shielded wire either. It is a single wire sensor. So, maybe this is the non-sheilded type? I'll take a closer look at the black wire to see if it is shielded. It has plastic coating, so maybe not.

I drilled a new hole yesterday for the new sensor and welded on a nut that the sensor will screw into. Ran out of time and got side tracked, so I haven't hooked up the wire yet. Gave up on the idea of dropping the exhaust for now. We'll see if the new one will do the job. I need to look closer at the shielding issue though.


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## smj999smj (Jan 1, 2006)

Shielded wires do have a plastic covering, or insulation. On a shielded wire, the signal wire is covered in a plastic sleeve, then the sleeve is covered in a very find braid of hairlike wires, which is covered by the outer, plastic insulation. So, what you have in the end is what looks like somewhat like a 14 gauge wire to the sensor. If the wire going to the sensor looks like a typical 18 gauge, insulated wire, then it is most likely not an shielded wire. I used to repair a lot of them when the bolt that held the bracket to keep the O2 wire off of the manifold used to fall out and the wire would end up melting to the heat shield of the exhaust manifold.


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## Smith1000 (Dec 29, 2005)

I took a good look at the wire. It is not shielded. I hooked up the wire to the new sensor and it is receiving volotage ranging from .25 to .8 or so. It may go higher. At idle it was reading about .25-seems kind of low, but maybe that is where it should be. If I rev the engine, the voltage climbs with each rev. It went up to about .8 before I stopped reving. I think the operation of the O2 sensor is probably normal. 

It still seemed rather rich though. The engine temp was reading about 1/4 of the way up the gauge. Maybe this is too cool of a running temp? I slid the cardboard that I was using during the cold part of the winter back in front of the radiator. It covers about 1/2 of the radiator. This raised the temp up to about 1/3 or slightly more on the gauge-still fairly cool. This seemed to improve the idle and reduce the black puffs of smoke during acceleration significantly. It really seemed to run better with the cardboard at the higher operating temp. I would say it is about where it should be and was idling even and a little faster than at the lower temp. 

Maybe I should replace the temp sensor sending unit? or put in a hotter thermostat. Might just leave the cardboard in there and watch the guage. May have to remove it as we get into the summer months. Where is the normal operating temp supposed to be on these trucks? 1/3 or eve 1/2 way on the gauge?


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## Fred S (Aug 26, 2006)

Smith1000 said:


> I took a good look at the wire. It is not shielded. I hooked up the wire to the new sensor and it is receiving volotage ranging from .25 to .8 or so. It may go higher. At idle it was reading about .25-seems kind of low, but maybe that is where it should be. If I rev the engine, the voltage climbs with each rev. It went up to about .8 before I stopped reving. I think the operation of the O2 sensor is probably normal.


That's normal. A one wire sensor has no heater, so at low RPMS it gets too cold to function properly. The computer should be ignoring the O2 sensor at these low temperatures, so it's not a concern.


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## Smith1000 (Dec 29, 2005)

I purchased a new temp coolant sensor today. Went to install it and found the wire detached from the one that is in it. Slid it back on and it runs fine. No more rich running. When I worked on the head, I detached the wire and broke the retainer clip off in the process. It vibrated loose apparently. I wired it in place today and, hopefully, that will take care of the problem. I hadn't noticed it was loose. It is kind of hidden under the intake manifold and the wire had dropped down out of sight.

Seems to be doing fairly well. I think I may pull the plugs and clean the carbon off. For the most part, I am done messing with it for now. Thanks for all the help.


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## Smith1000 (Dec 29, 2005)

Forgot to mention that the temp gauge in the truck had a reading all along. I had assumed it was working, but maybe not accurately. There must be more than one temp sensor?


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## smj999smj (Jan 1, 2006)

Should be one for the gauge and one for the ECM. The one for the ECM should be in the intake, near the thermostat housing and have a two wire connector and the one for the gauge will have a single wire connector. The one for the ECM is usually referred to as the coolant (or "water") sensor (Or ECT sensor) while the one for the gauge is usually referred to as a temperature switch ( "w/gauge" or "w/light"). 

I've seen a lot of aftermarket thermostats run a bit cooler than the Nissan OEM thermostats. My 97 HB always ran dead center on the gauge until I installed a Stant part, then it always ran about 1/3 on the gauge. I would recommend you install a new Nissan thermostat.


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## Smith1000 (Dec 29, 2005)

I may go ahead and do that. When I bought the truck, the thermostat in it was bad and it was running very cool and very rich. I replaced it with a Stant and it did run warmer and not rich, but it still hasn't seemed warm enough. I have been using the cardboard in front of the radiator to boost the temp up some. Even with the cardboard, it has never reached half way on the gauge-maybe 1/3rd or slightly higher. It seems to run better warmer and there is quite a bit of room left before it reaches the hot range.


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