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Old 12-23-2013, 09:40   #1 (permalink)
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Are both O2 sensors kaput?

So the boss bought her son a 1998 Ranger, 3.0. It has a p0171 and P0174 code which are usually vacuum leaks. I didn't see anything (though I didn't find the PCV) so i got out the scanner and started looking at data at idle:

O2S11: 157-805
O2S12: 0-662
O2S21: 122-751
O2S22: 0-0

Certainly the rear sensor on the #2 side (passenger side?) is dead but what about the other rear sensor?

Also, should I just start here and not worry about vac leaks unless I get another code? Are these known for leaking intake gaskets?
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Old 12-23-2013, 17:08   #2 (permalink)
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Re: Are both O2 sensors kaput?

I also have ST/LTFT information that I don't understand and don't know if it's useful.
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Old 12-23-2013, 17:10   #3 (permalink)
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Re: Are both O2 sensors kaput?

It's a 15 year old truck, I'd expect vacuum leaks, but eliminate the known before chasing the maybe's.
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Old 12-23-2013, 17:15   #4 (permalink)
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Re: Are both O2 sensors kaput?

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It's a 15 year old truck, I'd expect vacuum leaks, but eliminate the known before chasing the maybe's.
I know the 2-2 sensor is kaput, but I don't if the 1-2 is dead. Should it go to zero?
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Old 12-23-2013, 19:41   #5 (permalink)
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Re: Are both O2 sensors kaput?

What are your sht and LNG fuel trims. They are very important for lean code diagnosis. Ideally both should be about 0%. Usuall long term will be + or minus a few percent and shrt term will be floating around zero. A vacuum leak is usually indicated by fuel trims being high at idle and relatively normal at steady cruise. Any leak after the mass airflow sensor is an unmetered leak.
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Old 12-25-2013, 16:16   #6 (permalink)
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Re: Are both O2 sensors kaput?

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What are your sht and LNG fuel trims. They are very important for lean code diagnosis. Ideally both should be about 0%. Usuall long term will be + or minus a few percent and shrt term will be floating around zero. A vacuum leak is usually indicated by fuel trims being high at idle and relatively normal at steady cruise. Any leak after the mass airflow sensor is an unmetered leak.
Freeze frame data for the P0174:

STFT 1: 9.4
LTFT 1: 24.2
STFT 2: 21.9
LTFT 2: 25.0

I noticed at an idle, STFT 2 is cycling almost twice as fast as STFT 1. IOW, #1 may take 3 seconds to from high to low back to high, but #2 may take 1.75 seconds.

I have not looked at Trims while at a steady cruise. I'll do that tomorrow after I build the engine support for the Freestar.

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Old 12-26-2013, 05:34   #7 (permalink)
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Re: Are both O2 sensors kaput?

I'd say very possible vacuum leak. Maybe someone put E85 in it?


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Old 12-26-2013, 08:26   #8 (permalink)
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Re: Are both O2 sensors kaput?

E85... The previous owners own a couple of gas stations and I don't think they have E85 at their stations.

So a driving test is in order, correct? Warm engine, steady cruise, watching the trims on a graph.
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Old 12-26-2013, 11:22   #9 (permalink)
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Re: Are both O2 sensors kaput?

That and if possible check them cold. If it has the upper intake I-rings bad will only show cold. So basically need to know when it's lean. Hot or cold. Idle or cruise. If it's at idle it is usually unmetered air. If it's at cruise could be fuel issue or MAF problem


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Old 12-26-2013, 21:28   #10 (permalink)
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Re: Are both O2 sensors kaput?

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That and if possible check them cold. If it has the upper intake I-rings bad will only show cold. So basically need to know when it's lean. Hot or cold. Idle or cruise. If it's at idle it is usually unmetered air. If it's at cruise could be fuel issue or MAF problem


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So I need to look for when the STFT numbers stay low or high?
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