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Old 10-08-2013, 11:08 PM   #1
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Scanner readings and extremely sooty exhaust/bad mileage

My tail pipe is extremely black around the edge about 1/2"! I mean thick, thick black (about 1mm 1/16" or so!) I know these 4.0L's run rich, but this seems excessive and my mileage has dropped a lot since I got it last year (I was getting 400-410km's/tank last year, now down to about 310-340km's/tank.)
Mileage on the Jeep is 115k kms (~72k miles.)

I did a tune up over in the spring (plugs, air filter, oil etc) and it didn't make a difference as the stuff in it wasn't very old.

I hooked my lil Actron scanner up to it but am not getting any codes.

I am not totally sure where the readings should be for a Jeep so I'll list them if anyone can help to see if it's normal please?

Engine: 650 - 666 RPM
CALC (LOAD%): 4.3 - 4.7 -stays closer the to the first mostly
MAP ("HG): 11.2 - 11.5 -mostly closer to frist
COOLANT (*F): 207
IAT(*F): 153
IGN ADV (DEG): +10.0 - +12.3 -mostly closer to first
LT FTRM1 (%): 10.2
LT FTRM2 (%): 8.6
ST FTRM1 (%): 0.0 - +1.6 -mostly closer to first
ST FTRM2 (%): -0.8 - +1.6 -mostly closer to first
ST FTRM11 (%): 0.0 - +2.3 -mostly about 0.6
ST FTRM21 (%): -0.8 - +1.6 -mostly in middle
VEH SPD (MPH): 0
FUEL SYS1: CLSD
FUEL SYS2: CLSD
O2S11 (V): 0.14 - 0.80 -mostly in the middle
O2S12 (V): 0.800 - 0.820
O2S21 (V): 0.220 - 0.800 -mostly closer to last
O2S22 (V): 0.120 - 0.160 -mosty in middle
OBD2 STAT: CA

To me it seems the two O2s (O2S12 and O2S22) are stuck, but I think one is downstream? It's about $240 for 4 NTK O2 sensors up here, so only want to do them as last resort (thats a lot of cash to only increase mileage a bit!)

Thanks for any help or tips!

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Old 10-10-2013, 06:33 AM   #2
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What year?

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Old 10-10-2013, 06:47 AM   #3
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2004 TJ 4.0L more in my profile/garage...
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Old 10-12-2013, 02:05 PM   #4
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Have you inspected your air flow sensor?
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Old 10-12-2013, 03:34 PM   #5
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IAT of 153? Shouldn't that be closer to ambient temp? Not sure about the others. I'll go fire mine up to let it warm up and post back.
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Old 10-12-2013, 04:03 PM   #6
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Ok, the high IAT temp is due to just sitting there as mine is high too.

99 4.0 non-CA, Ambient Temp 90

ABSLT TPS (%) 17.6
ENG RPM 740
CALC LOAD (%) 4.7
MAP HG 10.6
COOLANT TEMP (F) 201
IAT TEMP (F) 149
IGN ADV 17.5
LT FTRM1 % 5.5
ST FTRM1 % 0
VEH SPD 0
FUEL SYS1 CLSD
FUEL SYS2 N/A
O2S11 V 0.3-0.8
ST FTRM11 % 0
O2S12 V .92
OBD2 STAT US
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Old 10-12-2013, 09:19 PM   #7
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These don't have MAF sensors I'm pretty sure Smitty4x4...
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Old 10-13-2013, 01:46 AM   #8
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You are right about not having a MAF (brain fart, I shouldnt post when tired). When there is no MAF, this will generally mean the upstream O2 sensor is going bad. When the upstream sensor tells the computer that the engine is running lean, the computer will richen the AF ratio and give the symptoms you are describing.
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Old 10-14-2013, 08:56 AM   #9
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Quote:
Originally Posted by IcarusLSC View Post
My tail pipe is extremely black around the edge about 1/2"! I mean thick, thick black (about 1mm 1/16" or so!)
...
O2S11 (V): 0.14 - 0.80 -mostly in the middle
O2S12 (V): 0.800 - 0.820
O2S21 (V): 0.220 - 0.800 -mostly closer to last
O2S22 (V): 0.120 - 0.160 -mosty in middle
....
Looks like your are reading 2 sensors from 2 banks, 4 total. Is this a cali-equipped jeep? Given the symptoms and this reading (bank 1 should be close to bank 2), my money is on a bad o2 sensor (bank 2 sensor 2 - 02s22).
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Old 10-14-2013, 01:45 PM   #10
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I'm pretty sure all of the '04 era Jeeps up here have 4 - O2s here for this year.

I would have thought the O2S12 looked like it was maxed/stuck too? The one before it seems to be in range so why would it be pegged? Mind you I'm no good with stuff like this, hence my post here and all the questions
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Old 10-14-2013, 03:20 PM   #11
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Originally Posted by IcarusLSC View Post
I'm pretty sure all of the '04 era Jeeps up here have 4 - O2s here for this year.

I would have thought the O2S12 looked like it was maxed/stuck too? The one before it seems to be in range so why would it be pegged? Mind you I'm no good with stuff like this, hence my post here and all the questions
I don't know jeep numbers and stopped learning obd2 a long time ago, but...

The first sensors should have a general degree of fluctuation and the second should be much more static. Your sensor 1 for both banks is doing just that as it goes higher or lower for rich/lean. The 2nd sensor should always read "clean" air, regardless of rich /lean conditions existing before the cat. So the 2nd sensor actually should somewhat peg towards lean, as it should read constant exhaust. Iirc, anyway.

One of your two is reading lean, the other rich. I just cant remember if up is lean or rich.
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Old 10-14-2013, 03:31 PM   #12
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Higher (up) is richer I know.

I'm more confused now the more I read as I always seem to get different answers on different forums and shops I talk too Even your two posts lead me to think different things (different sensors.) I hate tossing money at things, and do like to try and troubleshoot the proper way...
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Old 10-14-2013, 03:58 PM   #13
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Originally Posted by BlueRidgeYJ View Post

I don't know jeep numbers and stopped learning obd2 a long time ago, but...

The first sensors should have a general degree of fluctuation and the second should be much more static. Your sensor 1 for both banks is doing just that as it goes higher or lower for rich/lean. The 2nd sensor should always read "clean" air, regardless of rich /lean conditions existing before the cat. So the 2nd sensor actually should somewhat peg towards lean, as it should read constant exhaust. Iirc, anyway.

One of your two is reading lean, the other rich. I just cant remember if up is lean or rich.
I may have that backwards, idk for sure. I do know the 2nd sensor should be more static than the first.

Let's look at what we do know:

Our base info, from barb, is b1s1 .3-.8, b1s2 .92.
Our data from b1s1 is .14-.8, b1s2 .8-.82
Our data from b2s1 is .22-.8, b2s2 .12-.16

Which one is different from the other two?

Your pcm is likely reading b2s2 as lean and dumping fuel to compensate, which should peg the others at rich. Without a false lean reading you can't lose milage, only power. With a false rich reading you lose power, not milage.
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Old 10-14-2013, 04:07 PM   #14
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K, I see where you are getting that info now. I wasn't sure if comparing it to a '99 with 2 less less cats and O2's was a good way to do it though.

I tried to get my brother to help me with checking the cat temps, but he had to go back home. So I was looking under it today for a lil, need to do the rear main seal for sure and clean/do something with the clutch as it's chattering too now when cold but goes away as it warms up/drives, hopefully just from oil on it... Joy more things to fix
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Old 10-14-2013, 05:11 PM   #15
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Pony up and replace all 4 o2 sensors with the ntk version. Its what i had to do at around 90k miles recently. It helps. o2 sensors DO wear over time and slow down. If you like this Jeep and intend to keep it for a while its not tossing money at it with 4 new o2 sensors.
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Old 10-14-2013, 08:51 PM   #16
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I agree with Blue Ridge. You are describing an excessively rich condition. You have one sensor that is reading very lean. I would change the sensor. O2 sensors use a thin platinum filament that will wear over time. Prior to going bad you will get erroneous readings. All of them may be reading poorly but one appears to be way off. It may be time to change them all. One option is to unplug the suspected bad sensor. The ecm should throw a code for that sensor and go into open loop using a predetermined fuel map. If your problem is severe you should notice a difference when driving on the default fuel map. I have never done this because I usually just replace all of them around 80-100k miles when I start noticing a drop in mileage but if you really want to be sure in troubleshooting its one way. The other is to swap them. Upstream to upstream and downstream to downstream. The very low reading should move to where the suspected bad sensor was placed. You will then be confident when you replace it. When you swap in the new one you can also compare its reading to the other similarly positioned sensor to partially guage the quality of it's readings.
I'm not sure if this is true but I have heard the O2 sensor life is shorter in cold climates due to running winter fuel.
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Old 10-18-2013, 10:45 PM   #17
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I got some NTK O2's in the mail today along with rear main seal, Sachs clutch kit (first time ever doing a clutch!), and some other goodies to go with them (oil pan gasket, valve cover gasket, nice Iridium plugs, Wix filters, Mopar trans fluid thats made of gold flake I think from the price!!, lol... etc.) Looks like I have some work ahead of me
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Old 10-18-2013, 11:18 PM   #18
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I just found the form and thought I would way in on your problem. My Jeep buddy just had the same problem. He, like you, replaced all the usual components with no improvement. Not until he replaced the O2 sensors did he fix his problem.

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