Gen3 with continued O2 code?

cnutco

Adventurer
I have an '03 Limited that I bought from an older couple who never took it of road. This lady kept every receipt for everything she had done to the truck. Anyway she had all O2 sensors replaced sometime before I bought it.

I have had the truck for about 6 months now and have not done too much at all. The following has happened since I have had it.

The temp gauge does not work. This is a continued problem from last owner which they installed a new sender unit. I have been told that I would need to buy a new gauge and have the entire cluster reprogrammed which would be a min of $400.

Replace valve gasket covers due to leaking. Had new plugs and wires installed at the same time. The bank 2 sensor 2 O2 sensor code was on at this time too but it was new so we skipped it.

The light remained on and after the tune up the truck has started skipping only when accelerating mostly at top end.

So, we replaced the B2 S2 per the code. It was an OE Bosch sensor. After driving for only a short time the code came back on. The sensor is not reading steady and keeps dropping real low causing the code to come back on.

Any thoughts why the skipping and the O2 code is continuing?
 

cnutco

Adventurer
I do hope the right people see this post today...

Searching the web has led me to the following possible issues:
-Tune up needed (DONE)
-Injectors cleaned
-Replace PCV valve
-Replace catalytic converters​

The PCV valve is cheap enough to go ahead and do and I will look in the records provided by the previous owner to see if and when the injectors were cleaned, but what about the catalytic converters? Is there an aftermarket replacement that has a better design that provides better performance?

Has anyone replaced a CAT on their Montero?
 

Justice R

Adventurer
In my experience with the Gen 3, your probably looking at a bad cat. The first cat behind the exhaust manifiold. I believe they come as a pair wlded into the Y pipe. There's an aftermarket replacement that is cheaper than the stealer, but I cant vouch for the quality. I would replace the PCV and clean the injectors first though then replace cat last. You can bench clean the injectors yourself using a shade tree method (see youtube). Or you can take it to shop and have professionally cleaned with BB44K. I've done it myself before I like to visually see the spray pattern so there's no doubt that they are squirting. When was the last time the fuel filter was changed?

Cat went bad on my old 02 but I sold it before performing the repair.

By "Skipping" do you mean missing? That could point to clogged injector as a bad Cat usually will not cause a miss in my experience. So i would investigate that first and Hopefully I'm wrong about the cat being bad. The fact that you say its on the top end makes me think that a clogged cat might be causing detonation or pinging, different than a miss..

Also the OE O2 Sensors are Denso or NGK. Not Bosch. While the Bosch may wourk fine it would not be my first (or second) choice.
 
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cnutco

Adventurer
Thanks Justice!

I believe it had a Denso in it that looked new. I think I will be putting it back in and returning the Bosch. I think that Bosch had OE in the item because of the OE connector, which is miss-leading. I will take your advise and do the CAT last.
 

Justice R

Adventurer
Also, did you save the old spark plugs? You can tell a lot about whats going on in the combustion chamber by looking at the old plugs. You could take pics and post them. I'm no expert, but there are guys who ocan tell you just by looking at the plugs which cyl is detonating, missing, running lean due to clogged injector etc..
 

cnutco

Adventurer
Also, did you save the old spark plugs? You can tell a lot about whats going on in the combustion chamber by looking at the old plugs. You could take pics and post them. I'm no expert, but there are guys who ocan tell you just by looking at the plugs which cyl is detonating, missing, running lean due to clogged injector etc..

Noted! I will see if I still have them... THANKS!
 

kuroi

Chief mud inspector
What is the actual diagnostic trouble code it's throwing for the O2? and does the check engine light flash when it's "skipping"?
 

cnutco

Adventurer
I will have to write it down next time I plug it up.
The service engine soon light is on but not flashing.
 

cnutco

Adventurer
I never got back to this topic. It was driver side down stream O2 sensor. Light is off but it is still missing when accelerating.
 

RERM

New member
I had the same thing happen in December, had to get a Denso O2 for it to work, the Bosch replacements are no good. But now I'm getting another Code, something about the left bank (I'll get the code and post it later tomorrow). This is anoying the hell out of me....

03 Limited

Work done so far:

1. Timing belt replaced.
2. Water pump replaced.
3. O2 sensors replaced.
4. Accessory belt replaced.
5. Rear coolant hoses replaced.
 

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