[cvan1971man]

Got a 2002 4runner that just threw these codes out. This is my first time handling a OBDII scanner.

I am guessing that I have a bad O2 sensor. I borrowed a Foxwell OBDII scanner from a friend. After I figured out how to use it, I got these error codes. See 1st picture.

The 2nd picture shows the test results. The "O2 B1 S2" was at zero with just the acc on. When cranked the O2S B1 S2 fluctuated up and down.

The O2FT B1 S2 stayed at 99.15 both on ACC and when idling.

Long FT #1 fluctuated up and down as well.

I am hoping that there is someone smarter than I - Is this a bad O2 sensor, if so, which one is it - Upstream or Downstream?

The 3rd picture is running the Foxwell on the Catalytic Converter to see what it said. O2S B1 S2 was at 0.00 and AFS B2 S1 was at 3.29. I did not test this one while idling. I can if it was a bonehead move.

IS THERE A BETTER WAY TO DETERMINE WHICH O2 SENSOR IS OUT? OR AM I BARKING UP THE WRONG TREE!

[heat]

You have three different issues, of which only #3 might relate to the O2
sensors. Picture 1 gives you starting points for diagnosis.

[jgue467]

Work on the miss first, either a plug - most likely, coil (though you'd have 2 misses since 1 covers 2 cylinders. Switch coils around to see if miss changes and go from there. Luck.

[Bad Luck]

Originally Posted by jgue467

Work on the miss first, either a plug - most likely, coil (though you'd have 2 misses since 1 covers 2 cylinders. Switch coils around to see if miss changes and go from there. Luck.

A bad coil can cause a misfire on only one cylinder since there are two sides to each coil pack. It happened to me and it took me a long time to track it down. Only misfired when it was hot on cylinder #3.

[brillo_76]

On the cylinder that's misfiring. You can swap it with another coil to see if it miss moves with the coil. As you be using same plug and wire. This can help eliminate which Part is bad. If it stays at that cylinder it rules out the coil and leaves only the wire or plug causing the issue. If it moves with the coil. The coil is causing it.

Sent from my SM-A536V using Tapatalk

[spartacus]

Could also be a bad injector, unburned fuel causing the other code.

[cvan1971man]

So, I replaced the #1&4 Coil - did not fix the problem - still have a misfire code

- replaced the spark plugs

- Replaced the downstream O2 sensor - I thought a bad O2 sensor could cause rich fuel conditions which could cause the plug to foul. When I ran the OBDII scanner, it looked like that sensor was not fluctuating and I thought it might be bad - it did not fix the problem.

- Now getting new error codes - see picture below.

Any ideas?

[Bad Luck]

Originally Posted by cvan1971man

So, I replaced the #1&4 Coil - did not fix the problem - still have a misfire code

- replaced the spark plugs

- Replaced the downstream O2 sensor - I thought a bad O2 sensor could cause rich fuel conditions which could cause the plug to foul. When I ran the OBDII scanner, it looked like that sensor was not fluctuating and I thought it might be bad - it did not fix the problem.

- Now getting new error codes - see picture below.

Any ideas?

Do a compression test. If your compression is good then I would suspect #4 fuel injector is bad.