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  #13  
Old 06-23-2015, 09:14 AM
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Re: p0171 1999 grand cherokee

As far as i know they only used Denso as OEM for the 99-04 WJ. Donīt know about NTK, but Bosch sensors can give problems on jeeps, because they heat up more slowly and can give fault messages because of that. Just out of my night shift and will go sleep a bit now, i will see if i can find the site where i bought my O2 sensors from lateron.

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  #14  
Old 06-25-2015, 12:26 AM
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Re: p0171 1999 grand cherokee

Well.... It has been 2 days and the beast ( i call him shrek because he is big and green) has thrown no codes. I plug in the scanner after drive to work and back home to check live data. All is in normal range.
I am going to order both upstream o2's to be safe. I think rockauto had best price up front, but i can get 20% off at autozone because my son works there. I can also have now rather than wait for shipping.

Will update when i am done.


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  #15  
Old 06-25-2015, 11:57 PM
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Re: p0171 1999 grand cherokee

So just to make sure that i understand what is going on...
P0171-- the pcm is detecting a lean run situation via the upstream o2 sensor bank 1, so is then adding fuel to the mixture.

Since there is only 1 air intake (via the throttle body) and if all the injectors are firing correctly, if there were a problem with the map sensor, it would show a fuel mixture problem on both o2 sensors.

Since it is only on bank 1 of 2, it would point to a single o2 sensor being the issue. Rather than a systemic problem.

Does that all make sense from a pcm logical stand point?


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  #16  
Old 06-26-2015, 07:25 AM
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Re: p0171 1999 grand cherokee

Quote:
Originally Posted by chefjacques View Post
So just to make sure that i understand what is going on...
P0171-- the pcm is detecting a lean run situation via the upstream o2 sensor bank 1, so is then adding fuel to the mixture.

Since there is only 1 air intake (via the throttle body) and if all the injectors are firing correctly, if there were a problem with the map sensor, it would show a fuel mixture problem on both o2 sensors.

Since it is only on bank 1 of 2, it would point to a single o2 sensor being the issue. Rather than a systemic problem.

Does that all make sense from a pcm logical stand point?
Yes, that is right.
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  #17  
Old 06-29-2015, 10:29 PM
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Re: p0171 1999 grand cherokee

So Shrek has been running like a champ last few days, no p0171 codes, cel light staying off, until today.
Did some extra highway driving today and it was running great all day, and still is except that the cel came on and threw p0300, p0304, p0306.
I know 300 random misfire multiple
304 random misfire cyl 4
306 random misfire cyl 6

Is there any way this could be connected to previous issue??


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  #18  
Old 06-30-2015, 03:31 AM
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Re: p0171 1999 grand cherokee

You didnīt change the O2 sensors yet?
Cylinder #4 and #6 exhaust gasses pass by the 1-2 O2 sensor. Did the engine run rough at any time, or did it just throw the codes? When it really misfires, you normally feel it at a rough running engine.
Did you check the STFT for both banks? If maybe bank 2 has a large (double digits) negative number? (from dowm trimming the fuel too much, causing a real too lean mixture which doesnīt burn well and could cause misfires)
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  #19  
Old 06-30-2015, 07:29 AM
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Re: p0171 1999 grand cherokee

Just codes. No actual rough running.
Life was much simpler to work on cars with all the computers to confuse the issue


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Old 06-30-2015, 07:31 AM
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Re: p0171 1999 grand cherokee

And no, have not gotten to o2 sensors yet. 16 hour days for the past week with no days off till july 6


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  #21  
Old 06-30-2015, 09:54 AM
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Re: p0171 1999 grand cherokee

Live data just after startup.
O2s 1/1 voltage .1-.8 changing rapidly
O2s 1/2 voltage hovering around 1.0 +- .2 sluggish movement.

I will be replacing both o2s on monday next week. Will try and limit driving till then


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  #22  
Old 06-30-2015, 11:53 AM
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Re: p0171 1999 grand cherokee

The 1-2 sensor you mentioned is the after cat sensor for bank 1, that sensor should have a little fluctuating voltage. The amount of oxygen after the cat should be low, since the cat will use the oxygen to change the bad gasses in less bad.
But being almost fixed at 1.0V doesnt seem to be good.
How are the 2-1 and 2-2 sensors? How are the STFT for both banks?
I would errase the set fault codes and see if they come back.
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  #23  
Old 06-30-2015, 01:07 PM
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Re: p0171 1999 grand cherokee

I need to check all of them again when i leave work today. I keep getting the sensors mixed in my mind.
First number is bank
Second number is location (upstream or down stream) just need to keep straight.


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  #24  
Old 07-07-2015, 04:46 PM
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Re: p0171 1999 grand cherokee

So... I finally got to the new O2s. Removal was WAY easier that i have dealt with on other cars with less mileage. (Shrek has 205000). I am attributing it to being in the manifold rather than in the cat further down the line.
Anyway, once fired up, no codes popped up. It could have been my imagination, but it seems to be idling smoother than before.
I hooked up the the handy scan tool to monitor live data, and voltages and fuel trim numbers seem to be within what we have been talking about. Let car warm up and all seemed to be well with the car gods.

I am getting ready to make a minor road trip ( 30 minutes highway speed each way) and will get back with how it goes.
These are the sensors i pulled out. At least they are pretty clean.


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