Should I replace the O2 sensor ??

[Mellemel]

Looking for suggestions/advice on this issue, 366,000 on my '97 3.4 4runner, and
over 6 months ago I had fault codes for a cylinder 5 misfire and the downstream O2 sensor. It began with the misfire and then would dissappear for a few weeks then come back. I used seafoam and injector cleaner in the tank which seemed to improve some, but came back a few weeks later. Changed all plugs and it cured the problem until this week. Same codes came on. So plugs are newish, 8,000km on them, leads changed, injectors checked, coils checked all are ok ! I noticed the volt reading is 0.0v on the downstream O2 sensor at all speeds. This can't be right ! I saw it go up to 1.1v briefly then back to 0.0v, should I replace the O2 sensor ?

If the O2 sensor is not working am I correct in thinking it will throw out the mixture setting and cause a lean run causing the #5 misfire ?

I have read that a new O2 sensor has cured some peoples misfires, others say it makes no difference to replace the sensors ??

Can anyone shed any light on this ?

BTW codes are P0141 and P0305

 

[MrRoo]

Get a new sensor in there! I had some random drivability and lean rich codes with misfire once in a while. O2 sensor caused all the issues. They only seem to last 100k anymore. Mine is on its 3rd in 235,000. All OEM. 60,000, 130,000 with a new convertor at that time then I just put one in again at 233,000.

 

[1998Yota4Runner]

Try Berryman's B12. I used it when my check engine came on for my O2, within a couple days the engine was running better and I went from 210 miles a tank to 250 miles a tank.

 

[sterbenlicht]

It's probably a dead sensor, yes, but I don't think it's causing the misfire. It's sensor 2, not affecting the engine. If it were sensor 1, I'd definitely focus on the sensor first, but you'd also probably have a variety of erratic performance issues.

For the misfire, I would start with some easy things like moving the plugs and injectors around to see if the situation changes. Is it a constant misfire basically 100% of the time or is it just intermittent and only slightly noticeable? If it's constant, it's easier to track down.

Factory service manual direction:
-Open or short in engine wire
-Connector connection
-Vacuum hose connector
-Ignition system
-Injector
-Fuel pressure
-Mass Air Flow meter
-Engine coolant temp. sensor
-Compression pressure
-Valve clearance
-Valve timing
-PCV valve and hose
-ECM

 

[Mellemel]

Thanks for the replies guys, Ok so I have the 4runner booked in for the sensor replacement Monday am, I am not going to tackle that job, after 366,000km there is some serious rust that will need some heat applied etc... to remove it !!

A new set of NGK ignition leads ordered. I did the screwdriver trick to listen to the injectors firing, actually I could feel a real strong click through the driver ! #5 feels fine !

However, it makes me think I may have some build up again on that injector as over 6 months ago when I got this I used 2 cans of injector cleaner which seemed to cure the misfire, at least until this week. The misfire is intermittent and engine temp doesn't affect when it happens either. It can suddenly run fine when driving then suddenly start missing. I do notice it shakes and knocks more when I press the gas pedal but will still misfire but run easier when not accelerating, maybe a fuel delivery thing ! clogged injector ?

The only think I have done differently in the past 6 months was to almost fill the gas tank a few days before the misfire happened ! I hardly think that was responsible !

I'm going to use 2 cans of Wynns concentrated injector cleaner again, get the new plug leads on and have the sensor replaced and if need be go from there and work thru that list from above.

Just put on a new set of bootees for the snow can't be having a misfire !

 

[19963.4lsr5]

When it's acting up I'd jump out and check fuel pressure. The tester it 20 dollars at harbor freight.

 

[Mellemel]

Drove the car 50 km+ today and not a hint of a misfire !!! Could be the injector cleaner is working already ! Anyway, putting new O2 sensor in Monday am. NGK leads inbound from Amazon.