o2 sensor question (1 Viewer)

[dallen341]

Ever since I had a new exhaust system put on my 1989 FJ62 it has idled a bit rough and runs different. I can't qualify different other than at 2300 rpm's it seems to have a small boost in power. For some reason I had always suspected that the two o2 sensors had been placed in the wrong exhaust pipes. I finally checked tonight and it appears that the exhaust pipe for the forward bank of cylinders has the o2 bung and sensor for the rear bank of cylinders and vice-a-versa.

So the $64k question is does anyone know if the computer knows the difference if it is getting front bank info from the rear bank o2 sensor and vice-a-versa? I would think that it would, hence the two different sensors, yet I'm not sure how the computer works.

Thanks...Don

 

[benw4x4]

Is one of them heated? If not then all that the computer reads is resistance you may have a problem with back pressure.

 

[dallen341]

o2 question

I believe they are both heated. One serves the front three cylinders and the other serves the rear three cylinders. I'm guessing each bank of three cylinders has it's own control loop, but am not sure. Thus my ?

Thanks...Don

 

[dd113]

The sensors are the same from side to side. I have switched leads from one sensor to another with no negative results so I dont think it matters. We have also considered doing away with one sensor and doubling the wires to the new single sensor. It should work just fine but we have not tested it yet.

Have you run the codes and done the OEM test on the sensors. We find that even if they pass the test some are still bad and need replacement. Usually the symptom of a semi-bad sensor is a rough idle that can ONLY be explained by the O2s. That is: everything else in the system, that could possibly cause a rough idle, is either new or known/tested good.

 

[Rogorn]

Good time to ask this question! <grin>

It has been explained to me that the signal from the O2 sensors is not looked at (by the onboard computer) until the engine reaches operating temperature. Thus, the source of a rough idle, hesitation, etc. at start-up lies some where else. Meaning, not with the O2 sensors, correct?

 

[dd113]

Good time to ask this question! <grin>

It has been explained to me that the signal from the O2 sensors is not looked at (by the onboard computer) until the engine reaches operating temperature. Thus, the source of a rough idle, hesitation, etc. at start-up lies some where else. Meaning, not with the O2 sensors, correct?

Pull clean and test your cold start injector and the cold start BVSV.

 

[Rogorn]

Thanks, DD.

Color me "too-new", what is the "BVSV"?

 

[dallen341]

The sensors are the same from side to side. I have switched leads from one sensor to another with no negative results so I dont think it matters. We have also considered doing away with one sensor and doubling the wires to the new single sensor. It should work just fine but we have not tested it yet.

Have you run the codes and done the OEM test on the sensors. We find that even if they pass the test some are still bad and need replacement. Usually the symptom of a semi-bad sensor is a rough idle that can ONLY be explained by the O2s. That is: everything else in the system, that could possibly cause a rough idle, is either new or known/tested good.

I replaced the sensors at the same time I had the exhaust syystem done. I used Toyota o2 sensors.

Thanks...Don

 

[dd113]

Thanks, DD.

Color me "too-new", what is the "BVSV"?

It is Bi metal vacume switching valve but you dont have one! I was thinking Fj60??? WHo knows. You have a cold start injector time switch on the thermo housing. There are resistance checks to do on it to make sure it works correctly.

 

[USMC88Fj62]

Help! I am new to the forum and a novice mechanic. Had my 1988 FJ62 throwing codes 25 and 26 so I went ahead and purchased new O2 sensors. Just needing the location and best way to replace them. Thanks!

 

[ekberger]

If you have the new O2 sensors in hand you'll know what they look like and if you look at the forward section of the exhaust pipe you will see them. The difficulty will come from trying to remove the old rusted nuts; 2 each per sensor. I found that no amount of PB Blaster would do it. I finally had to grind the nuts in two with a die grinder and split them with a cold chisel. Perhaps you could cut with something like a Dremmel but the difficult part is getting in there as there is very little room to work. I was careful enough with my die grinder to not cut into or damage the threads on the studs. The other part is just to unplug the wire harness. Replace all nuts and the 2 gaskets.

 

[ekberger]

Also don't know what brand O2 sensor you purchased but those more knowledgeable than me told me to use the Denso sensors in my 62 vs the Bosh. So far they work as advertised.

 

[dbenke]

I heated them red hot with a torch and they came right off

 

[USMC88Fj62]

Thanks guys