Running rich after O2 sensor change - JeepForum.com

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post #1 of 99 Old 01-06-2012, 06:14 PM Thread Starter
Bad_Dog
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Running rich after O2 sensor change

I replaced my O2 sensor a couple of weeks ago. At the time, it was throwing code 21 (Oxygen Sensor Circuit) and 51 (Oxygen Sensor, Lean condition). Before I changed it, I cleared the codes a few times and would alternate between 51 (lean) and 52 (rich), but always got 21.

Replaced the O2 sensor and now I'm getting 52, running rich. I've cleared the code twice and still it only gives me 12, 52, and 55.

Back story... Before all of this, the Jeep was running fine. I started to replace the O2 sensor as a precautionary tune-up in November, because I've had the Jeep for six years and never replaced it and wasn't sure if/when it was last changed by the PO's. It was seized and I couldn't get it out, even after a LOT of PB blaster and elbow grease. After all of that, and disconnecting it a few times, it eventually led to error codes 21 and 51, which I figured is from the overuse of PB blaster that eventually put the nail in the coffin for the sensor. Ended up taking it to a shop and had them remove it and install the new sensor that I had already bought.

Is there something I should check with the O2 sensor to ensure it's working? Put a meter on it? Is there something else I should check? I'm at a loss.


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post #2 of 99 Old 01-06-2012, 07:21 PM
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You probably have a leak or crack in your exhaust system before the O2 sensor. The O2 sensor that was doing its job picks up the excess O2 in the exhaust gases which it 'sniffs' causing a false lean condition.

The PCM then dumps extra fuel to burn with that 'extra O2' that is not going through the cylinders.

Do you know what was good about the good old days? I wasn't good, And I wasn't old!

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post #3 of 99 Old 01-06-2012, 07:35 PM Thread Starter
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Ugh. I'll have to crawl under it and see if I see leakage. What are my options... can I use JB weld if it's a small crack?

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post #4 of 99 Old 01-06-2012, 08:00 PM
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How long have you ran it? I have heard theories that new O2 sensors sometimes need to heat cycle a few times before they work properly.

All about that unibody life.
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post #5 of 99 Old 01-06-2012, 08:17 PM
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Originally Posted by Bad_Dog View Post
Ugh. I'll have to crawl under it and see if I see leakage. What are my options... can I use JB weld if it's a small crack?
IF you have a leak it may be a hole in the exhaust pipe or a loose exhaust manifold to exhaust pipe flange. I do not think that JB Weld would fix a manifiold or that would be the known repair of choice.

Check to make sure the throttle body is bolted down tight also.

I had a cracked exhaust manifold on my YJ. There was no way to fix it while it was bolted onto the engine. Welding them up is usually only a temporary fix as I understand it.

You can usually hear an exhaust leak.

I bought another aftermarket unit on EBAY and swapped it out along with a new intake/exhaust gasket. FYI my engine was running rich before the exhaust manifold swap and the CEL was lit up with the same codes.

BUT, Verify that you have extra O2 getting into your exhaust system before the O2 sensor but after the combustion chambers before you move forward.
One example of another possibility is; If your MAP sensor has poor vacuum it can cause the same issue. It uses manifold vacuum to tell the PCM where you are in the RPM range. That can cause all kinds of issues becasue of the conflict of reports woth other sensor reports.

Do you know what was good about the good old days? I wasn't good, And I wasn't old!

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post #6 of 99 Old 01-06-2012, 08:30 PM
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X2 checking for exhaust leaks... I knew my headpipe was OK so I tried tthe manifold bolts onto the head... they were all loose. So check those, in addition to the throttle body as mentioned. X2 on the MAP sensor, check all the vacuum lines with some carb spray around the ends while it is running.
.
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post #7 of 99 Old 01-06-2012, 08:32 PM
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that's funny because since i've been running poor lately and i can't buy the new o2 sensor i need
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post #8 of 99 Old 01-06-2012, 08:50 PM
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Regards testing the o2 sensor, you can hook up a decent code reader and it will tell you the o2 sensor readings.

Martin

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post #9 of 99 Old 01-07-2012, 06:47 AM
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Quote:
Originally Posted by Bad_Dog View Post
I replaced my O2 sensor a couple of weeks ago. At the time, it was throwing code 21 (Oxygen Sensor Circuit) and 51 (Oxygen Sensor, Lean condition). Before I changed it, I cleared the codes a few times and would alternate between 51 (lean) and 52 (rich), but always got 21.

Replaced the O2 sensor and now I'm getting 52, running rich. I've cleared the code twice and still it only gives me 12, 52, and 55.

Back story... Before all of this, the Jeep was running fine. I started to replace the O2 sensor as a precautionary tune-up in November, because I've had the Jeep for six years and never replaced it and wasn't sure if/when it was last changed by the PO's. It was seized and I couldn't get it out, even after a LOT of PB blaster and elbow grease. After all of that, and disconnecting it a few times, it eventually led to error codes 21 and 51, which I figured is from the overuse of PB blaster that eventually put the nail in the coffin for the sensor. Ended up taking it to a shop and had them remove it and install the new sensor that I had already bought.

Is there something I should check with the O2 sensor to ensure it's working? Put a meter on it? Is there something else I should check? I'm at a loss.
Does the jeep start and run bad,or are you having a hard time starting it?
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post #10 of 99 Old 01-07-2012, 07:02 AM
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Quote:
Originally Posted by leftlanetruckin View Post
Regards testing the o2 sensor, you can hook up a decent code reader and it will tell you the o2 sensor readings.

Martin
For that matter, all you need is a decent multimeter. On the "sense" wire you should see about 0.5 volt running while hot, if its right. It'll hover between 0.4 and 0.7, where the higher the voltage, the richer it is. I'll have to dig out the Hayne's manual to get the color of the wire.
.
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post #11 of 99 Old 01-07-2012, 07:08 AM
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There are other possibilities for your troubles.

Let's say that your exhaust has no leaks but excess air is getting to the O2 sensor and causing a code 52 to pop up.

Maybe the O2 sensor is it not tightened up enough or the wires from it are brunt OR the O2 sensor was cross threaded when it got installed.

Do you know what was good about the good old days? I wasn't good, And I wasn't old!

Senators and Congressman should wear uniforms like NASCAR drivers so we could identify their corporate sponsors....
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post #12 of 99 Old 01-07-2012, 08:43 AM Thread Starter
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Quote:
Originally Posted by Xpress View Post
How long have you ran it? I have heard theories that new O2 sensors sometimes need to heat cycle a few times before they work properly.
Been driving it daily to work for the past three weeks.

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post #13 of 99 Old 01-07-2012, 08:45 AM Thread Starter
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Originally Posted by oldtime_ironman View Post
For that matter, all you need is a decent multimeter. On the "sense" wire you should see about 0.5 volt running while hot, if its right. It'll hover between 0.4 and 0.7, where the higher the voltage, the richer it is. I'll have to dig out the Hayne's manual to get the color of the wire.
.
I moved to a new house last year and the ONE thing I set aside is my Haynes manual. I moved it and my computer equipment into the house, first. NOW that everything got moved in, I can't find it.

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post #14 of 99 Old 01-07-2012, 08:46 AM Thread Starter
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Originally Posted by laybackman View Post
There are other possibilities for your troubles.

Let's say that your exhaust has no leaks but excess air is getting to the O2 sensor and causing a code 52 to pop up.

Maybe the O2 sensor is it not tightened up enough or the wires from it are brunt OR the O2 sensor was cross threaded whn it got installed.
I haven't looked at the workmanship of the shop to see how good of a job they did. It may be something simple as cross-threaded. Hope so - that's easy to fix.

I'm just concerned that because the original sensor was seized that they did a lot of banging on it to remove it, and may have cracked it during the process.

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post #15 of 99 Old 01-07-2012, 08:48 AM Thread Starter
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Originally Posted by nembudonna View Post
Does the jeep start and run bad,or are you having a hard time starting it?
It does start. After I reset the codes, the first start-up, it's fine (I'm in NY and it's been very cold the last few mornings). After the first or second startup, it would run like it's hesitating. A lot of smelly exhaust. But after it warms up, it seems to idle fine. If I start it up and try to step on the accelerator before it warms up, it sounds like it's wanting to stall - I'm guessing that it's getting way too much gas and choking.

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