FJ62/3FE Potential O2 Sensor Failure

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Hey all,

I've been digging around the forums finding other forums with similar behavior to what I'm seeing with my truck,

What my truck is currently experiencing(236k miles):

  • CEL on highway after long operation under continuous load, 45m-1.5hr
  • Seemly reduced fuel economy, down to 1/4 tank after 110mi highway

Based on this forum post: FJ62 questions - O2 sensor and EGR - https://forum.ih8mud.com/threads/fj62-questions-o2-sensor-and-egr.1033273/

I'm leaning towards the O2 sensors having let go, especially since there isn't any documentation of them ever having been done on the truck. What does kinda confuse me though, is I don't have a rough idle or noxious smells from the engine bay beyond the natural old Toyota musk. The other thing is, I think spark plugs haven't been done by myself in the time I've owned this rig, but idk if those getting weak would throw a CEL.

I also haven't learned how to read OBD1 codes yet, but getting the CEL to appear and stay on is tricky since it takes such a long operation time to get it to appear, and it's not a given either. More of a road trip situation where it'll occur. I'm digging through the FSM now to see if I can find more troubleshooting info about O2 sensor issues or if I'm on the wrong trail.
 
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After taking a look at the O2 sensors, I’m not wondering if it would be better to replace the down pipe as well. The unshielded one looks fused to the metal via rust.
 

OSS

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It would be kind of astonishing if a 32 year old O2 sensor worked just as well as a new one…
 
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It would be kind of astonishing if a 32 year old O2 sensor worked just as well as a new one…
Yeah for sure, I can’t verify if these are original or not but they do seem due to be replaced anyway. I’m not sure if the Denso units from Advance Auto are a direct fit, I think I was reading on here the wires are too short.
 
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If you click on 'info' by the Denso part number, Rock Auto often provides the OEM part number, which allows you to correlate with Toyota. I have purchase all my Denso oxygen sensors there for years.
 
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Looks like they have the sensors and the gaskets, but not the nut. May need to source those from the local hardware store.
 
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This is the state of the lower O2 sensor attachment point, had it soaking for a few days in PB Blaster. Not much to grab onto, going to try a wrench and maybe a bolt extractor. These down pipes may be beyond saving.
 
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Hmm, yeah this is gonna need to get cut out at the cat and new downpipes installed.

I don’t think I can get my angle grinder to the bolts at the cats without damaging the surrounding area.
 
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Ah, rockauto has the downpipes for cheaper: 1988 TOYOTA LAND CRUISER 4.0L L6 Exhaust & Emission Parts | RockAuto - https://www.rockauto.com/en/catalog/toyota,1988,land+cruiser,4.0l+l6,1276613,exhaust+&+emission,pipe+/+resonator,10038https://www.rockauto.com/en/catalog/toyota,1988,land+cruiser,4.0l+l6,1276613,exhaust+&+emission,pipe+/+resonator,10038v

Might reach out to a local shop about fabbing up a new setup.

If I can find a good way to cut the downpipe bolts at the cats and loosen the manifold bolts, I might be able to DIY the pipe swap.

None of the sockets in my set fit the manifold side bolts though, my set goes 13, skip 14-15, 16 with 13mm being too small and 16mm being too large.
 
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Engineer8000

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Sometimes the O2 sensor wires and/or connectors will contact the exhaust pipe and melt. Did you check your wires/connectors? There is also a test for the O2 sensors in the 3FE FSM, page FI-75. If a bad O2 sensor you might get a code 21 or 28 from the ECU. You are heading toward a difficult project replacing the down pipes and sensors it would be worth doing further troubleshooting first. I hate working on exhaust.
 
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Got the truck back from the muffler shop, turns out we only needed to cut out the old bungs and weld in new pipe. It’s not winning any show awards, but the truck is more steady under power now. Will update if the road-trip CEL returns.
 
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