Bank 1 means all 6 cylinders collectively. If there was a O2 sensor fir each cylinder bank before going into the Cat then we would have a bank 1 and bank 2.

So, whatever is happening is that it thinks it needs to reduce the fuel mapping by 10 percent (-10 LTFT).

What speed were you driving at or was it at idle? At idle it will pull fumes off the EVAP and you will see a negative number.


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Hi

I can try to add as well. My 99 has a GASSY + exhausty smell and the power is not consistent. I have new wires + plugs as well. No CELs.
Further investigation, I can see the manifold/header gaskets need to be replaced as well as fuel injector o-rings (thanks to the gas smell in the cabin).
I have yet to tackle it as I just bought 2 more 3rd gens and they have my attention. (pictures coming soon!!!)

I hope that kinda helps on other places to check.

Those numbers were at idle after the initial startup but after a minute or two, the STFT settled around zero (+/- 3%).

It definitely runs the worst at startup for the first 5 minutes or so, after it is warmed up, it runs completely normal.

If I shut it off and let it sit for 30 minutes or so, the roughness returns.

What is the LTFT driving down the road?


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I'll have to check that and report back.

And how soon after startup does it go closed loop?


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Did you have the undercarriage sprayed when going through the car wash? If so, the o2 sensor or wiring might of got damaged if it’s old and brittle.

O2 wiring is fine, just checked it. Unfortunately I doubt I'm going to be able able to get the Upstream O2 sensor off. The nuts are literally almost non existent. One almost looks entirely gone and the other is a round rusty mess the size of a pea.

I tried swapping the MAF but its still running rough. Haven't had time to take it for a spin since I got the kids and the wife's working. Not sure what I'm going to do about the O2 sensor.

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I had to remove the down pipe to get the O2 sensor off. Once the downpipe was off, removing the O2 sensor was easy. Unfortunately, one of the studs broke off on the down pipe flange. Not sure how I'm going to fix that, it's the one closest to the engine.

Also, I found this. There was a crack near the O2 sensor flange. The metal is super thin and rusty so I busted out the welder I just got (I'm not a welder BTW). I did my best to plug it up and I was successful. I basically had to make blobs of weld and slowly connect them to keep it from blowing through (machine was turned all the way down). It's ugly but solid.

Tomorrow I'm going to get the downstream sensor off. I'll need to figure out what I'm going to do with the broken stud on the exhaust flange.

If the O2 sensors don't fix the issue, I'm going to swap the injectors next.

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Drilll out the broken stud and re tap it and use a hardened bolt.


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I don't see how you could ever get a drill in there. I'd have to remove the next peice that goes to the manifolds which would probably lead to more broken studs.

Not sure what to do.

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Ok so you never pulled the CAT.....on my 96 and 97 the front sensor is in the pipe with cat and the rear sensor is with the muffler section.
sadly you will need to pull it to fix it.


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I have a modified setup due to my cat being stolen when my truck was my brother's. So my downpipe is actually part of the old cat. He had an exhaust place weld on a universal cat. I'll see if there is anyway to get the stud out with it in, if not, I'll have to pull that peice of exhaust off the headers.

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Looks like you're in the right direction - I had similar symptoms on an old O2 sensor after getting it wet / through puddles and streams. O2 sensor wiring looks fine, but engine would stutter and die after more water exposure. New O2 sensor was the easy cure.

Depending upon how much of the stud is left, you can try to weld on a new nut to the stud. Soak with oil for a good long while, multiple times, then blast the surrounding area with MAP gas just before trying to remove. Say a prayer it doesn't break again.

A friend of mine worked at the local Toyota dealer and said they always removed the studs and used bolts.


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