O2 sensor replacement

[uwbradley]

I have a 91 Navajo with the 4.0. I took my truck into the shop to get some stuff done to it and I had them scan for the check engine light. They didn't tell me the codes specifically (well he did, but I forgot them), but they said I need a new MAF and a new O2 sensor.

After searching on the board, I have cleaned out the MAF before and I was wondering how often these "go bad"...it seems like cleaning them has been the answer all for all MAF problems.

As for the O2 sensor, I did some searching here on the board. I see that some people say they have two O2 sensors, but he was singular when he said that an O2 sensor had to be replaced...he said something also about "pre cat sensor"...if there are two on my Navajo, is there one after and one before the catalytic converter? Should I go ahead and replace them both? I mentioned that I know something about them (I changed them on my old CRX, piece of cake) and he immediately said that they are a bear to get to, and it was two labor hours alone to get to it. I didn't believe him. How hard of a job is it to go after "it" or "them"?

I am not worried about the MAF, if that even had to be replaced that would be a piece of cake. Any insight into the O2 sensor (or sensors) would be appriciated. Thanks!

Brad

 

[ipozestu]

There a piece of cake alright. I think that it is a 15/16 fitting. I'm not sure how many 02's you have pre cat but they are located on the manifold Y pipe on either side. Unplug 'em take 'em out and pop the new one(s). If you want to find which one it is. There is a gray/blue wire on the plug you can tap that wire. You should see the voltage fluctuate btwn. .6-1.0 volts. If it is doing this that sensor is ok. There is a sensor after the cat. Not sure if this is a possibility, so I won't comment.
Hope this helps,
Jeff

 

[KPT]

My 95 has two upstream O2's (before cat) and no downstream. I'm guessing your 91 might be the same.

They're very easy to replace... You can rent an O2 socket from Autozone or just us an open ended wrench.

 

[DeRocha]

I just happen to have my 91-92 Haynes manual in front of me. It indicates there is only 1 sensor for the 91-92 model years. Years '93 - '94 have 2. The sensor is located just just before the exhaust flange (where it meets the CAT). To remove you must first unplug the sensor wire. I am unsure where the connector is but my '93 was easily reached through the wheel well. I used an adjustible wrench to remove the sensor. Even though it was on for 10.5 years in New England weather it came out easily. They do make a special socket that fits onto a socket wrench to remove hard to access sensors. These are under $10 at most auto stores, but by the look of the picture in the manual it is a piece of cake to change yours.

 

[uwbradley]

Man! You guys are soooo helpful!! This has to be one of the best message boards that I have been a part of. I used to own a CRX for quite some time, and was a member on quite a few Honda boards. This one blows every one of those out of the water!!

As for the MAF, should I clean it again or just get another one? Thanks a TON...

Brad

 

[Premier]

Yea I have a 96 and changed the O2's in the front of autozone after parking on a parking block. Also I would just clean the MAF again to see if that gets rid of the problems. Once you do theese make sure to have your codes cleared. If they come back on have them read again and see if the MAF actually does need replaced.

 

[mjs232]

I need my front right O2 sensor replaced according to Auto Zone, and I think that i want to tackle this project myself. I am pretty handy in the sense that I could build you a house if you wanted, but when it comes to mechanics i can fill it up with gas and change the windshield wipers and thats about it. I want to learn more about mechanics and i think this is the perfect place for me to start. I got the 96 repair manual on CD, but this doesnt seem to say much about the O2 sensor. Is there any detailed thread that goes through the steps. I've watched my mechanic replace one of mine before but forget the details. I know it just screws in and wires snap to it, but are there any cautions i need to look out for? Do i need to put anything on the threads of the sensor? Thanx.

 

[DeRocha]

The O2 sensors (Bosch) should already come the anti-seize on them (remove the protective plastic cap when picking them up at the auto store. If they have a gray substance on them your set, if not pick some up) This stuff will prevent the sensor threads from welding themselves to the exhaust.

Also you should remove the negative battery cable before starting this project. This serves 2 purposes. First it prevents any accidental shorting of wires when you unplug/plug the sensors. Secondly it will reset the cars computer so it can work better with the new sensors.

 

[uwbradley]

Ok, so does taking the negative battery cable off reset the computer AND clear the codes? Do I need to get one of those things from Autozone to clear the codes?

When I cleaned the MAF for the first time, I used GUMOUT Carb cleaner and a q-tip. Could Gumout potentially have ruined the MAF? I saw that most everyone here uses "carb cleaner" but what kind was never specified really.

Brad

 

[Rhett]

Removing the neg cable for a while will reset the computer (and clear the codes, I believe..). If there's a problem though, it will soon throw a code again.

You can use any carb cleaner/electric contact cleaner as long as it says "O2 Sensor Safe" or "Safe for O2 Sensors and Throttle Bodies" or something similar. I always use STP Throttle Body and Intake cleaner. I wouldn't use a Q-tip, it's not necessary to touch the sensor to clean it...it could leave little Q-tip fibers on the sensor, not to mention touching the Q-tip to the sensor could knock it out-of-place a millimeter or two, enough to affect it's readings...