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Discussion Starter #1
I'll try and be brief:
- 2002 Duratec Sable
- Good shape 130K
- Replaced plugs and wires 50K ago (Motorcraft wires, Autolite Double Plats)
- Driving a week ago, started running rough and missing, CEL goes on
- I forget the 2 codes but it was saying that #5 cylinder was misfiring and that a misfire occured in first 1000 RPMS. (#5, what luck, right in the middle up front)
- The number 5 plug looked like it had a carbon arc running down the cermamic part
- Late at night so I swapped #5 and #6 plug (expecting to get a new code saying #6 was missing)
- Car ran fine, no CEL.
- About 15 miles later, still running fine, but CEL comes on. Code is P1151 (I did search the forum)
- I keep clearing the code but it comes right back, running fine.
- I replaced #6 plug with a new Autolite Double Plat, still running fine, code still coming on P1151

Ok, my thinking is that the plug misfiring was hurting the front 02 sensor (raw gas going by it???). This is called the upstream one right? Its the easy one to access right behind the radiator. Is there something else I should check or try? What would you do? Thanks for any help!
 

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At 130k miles the O2 sensors are due for replacement. I supposed it's possible that your theory of the misfire and unburned fuel damaged the O2 sensor... one that was already beyond it's life expectancy.

Yes, that is the upstream sensor. If you need to replace the sensor, I recommend you replace both upstream sensors at the same time.
 

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P1151 Lack of Upstream Heated Oxygen Sensor Switch - Sensor Indicates Lean - Bank No. 2

Rich mixture usually doesn't kill an O2 sensor. Lots of things can cause this code. The sensors are probably due for replacement. But rather than just throw parts at the code, you might want to try this. I wrote a diagnostic procedure for these lean codes. Read it here: Duratec Lean Codes
 

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Discussion Starter #4
RickMN you da Man! Thanks for the write-up. I will follow what you wrote and let you know what I find before I start throwing parts. I will start with the MAF sensor (I actually have a can of cleaner for it, I have had to clean these on other cars before).
 

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In my experience, a lack-of-switch code has always been a sign of a bad o2 sensor. PO171 / PO174 codes are the ones that are usually a result of vacuum leaks.
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X2

In my experience P1151 / P1131 has always been a failed sensor. A rich mixture will contaminate the sensor. I have never found P1151 to be connected to a vacuum leak or failed DPFE / EGR.

P0171 and P0174 together indicate a vacuum leak between the MAF and LIM. If either code appears by itself, it's generally a vacuum leak between the LIM and head on the affected bank.... which is usually a bad intake manifold gasket.
 

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Lets think about this some more.

Seeing as how he didn't have the code P1151 before replacing the plugs, do you suppose he didn't wipe the computers memory after the repair, to clear the old lean fuel trim tables it had learned for that bank, while the miss was present????

So now now that bank is trying to run with the old lean fuel trim.

So maybe try pulling the battery B- cable for 20 min, to wipe the computers memory & let it begin to relearn/rebuild it's fuel trim tables.

If he'll do this on a completely cold engine, then to enable it to relearn it's cold & warm idle strategy & restart it cold without any electrical loads on, let it idle down some, then shift into ALL gears, including "R", long enough to feel them engage, ending in "P", then let it fully warm up and shift into ALL gears again, without turning on any electrical loads.

Then drive it some in stop & go city/urban, then some highway miles, by then it should have relearned enough not to cause any undue driveability problems, until it completes it's relearn strategy cycle.

In the past after having the battery disconnected, I've never had to do any more than the idle relearn part.

So maybe wiping the computers memory to clear the code will do it, if it's just the computer being confused about not being told the miss repair was done!!!!

More thoughts for pondering. Let us know how it goes.
 

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Discussion Starter #8
Ok, here is where I am at.

- I checked the engine (again) for hoses loose or off, and found nothing
- I removed the MAF and cleaned it with MAF cleaner
- I unplugged the O2 sensor and cleaned the electrical connectors with both sandpaper and contact cleaner.
- I have one of the orange Actron code readers and resetters and have been traveling the past two weeks with that in my car reading and resetting the CEL. Does this reset ALL the codes? When I reset it and then read it again, no codes come up. Does this reset the trim information, etc?

One thing I noted was that after I did the MAF and electrical connector cleaning, the new codes that came up were P1151 AND P0153. Seems to be pointing to the 02 sensor. I went to Autozone and got a new one for $43 along with the tool to. Note after I cleared these codes, only the P1151 is coming up now. Note, that the car runs fine.
 

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Clearing the trouble code with a reader won't wipe the computers fuel trim tables.

If you don't want to take the time to pull the battery B- cable for 20 min to find out if wiping the computers memory will work, just continue driving it & see if it'll finally learn enough, to build new fuel trim tables & turn it off.

But if it's really running lean on that bank, I'd take the time to wipe the computers memory, rather than risk cooking a valve or plugs, or some other lean mixture or combustion chamber heat related mischief.

Let us know how it goes.
 

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Discussion Starter #10
Final Results!

Went outside in the cold this morning (Michigan 15 deg.). Took out the O2 sensor with the tool from AZ. Not too bad. Once it broke, it came out easily. Put the new one in and plugged it in. Note that was the tough part. Pins were not lining up and I kept having to move them until I got it to plug in.

Just got back from 25 miles of driving with roughly 10 start/stops. Not CEL. Code reader says no codes. So my thinking is the O2 sensor was bad and now it is fixed for about $45. Not too shabby. If for some reason it comes back on, I will repost, but I think this problem is solved.

Thanks for all the comments and feedback. Was a big help!
 

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I agree on replacing both O2 sensors at the same time.

I just replaced both O2 sensors on my 94 3.8L that would randomly set a code.
They had a little over 100K miles on them, one was lazy, the other was known to take a nap now & then...... kinda like pawpaw!!!! lol
 

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Discussion Starter #13
I only replaced the one. I have driven the car some more and no CEL and also no codes from the code reader. I may replace the other when it warms up a bit. How tough is the other? I assume I have raise up the car and get under it. I heard it was a bit recessed.
 

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Bank 1 Sensor 1 is cramped, but easier on the Gen 4 than the Gen 3 IMO. It will help to remove the cowl just as you would to replace the rear spark plugs. The Bank 1 sensor sits higher up on the exhaust manifold, so it's not as much of a stretch in a cramped space as it is on the Gen 3.
 

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If your new O2 sensor doesn't have a high temp nickel loaded anti-sieze compound on the threads, be sure to apply some, but DON'T get any on the sensor end of things.

I opted to get at my Gen-2 3.8L O2 senors by raising the vehicle on ramps & using my local Advance Auto's "Loan-A-Tool" programs O2 sensor socket removal kit. No problem at all getting to & removing both of those 15 year old OEM sensors.

Getting to the rear sensor on the Gen-2 3.8L was a little tight, but not really difficult. Required more time getting everything together & raising the vehicle, than actually changing the sensors out!!!!

The kits special notched O2 sensor removal socket & the fact that the factory had applied plenty of high temp anti-sieze compound to the sensors threads, made it easy to get those 15 year old sensors out!!!!

Be sure to pull the battery B- cable before beginning the job, so the computers old fueltrim tables are wiped, then after reconnecting the cable, take the time to go through the cold & warm idle relearn routine, for the computer, so you don't have any idle problems afterward & so it can begin to rebuild it's fuel trim tables with the new O2 sensors input.
If you have any driveability problems, post back & I'll look up a link for Fords drive relearn routine, that'll help the computer more quickly relearn what it needs too.

I just did the cold & warm idle relearn thing & didn't have any driveability problems, so I didn't have to do Fords drive relearn routine.

More thoughts for consideration.
 

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I don't know why everyone says to replace both O2 sensors when one fails. That's like saying "well, if your front brakes are shot, you might as well replace the rear ones too." Why would you replace parts that are working fine? We NEVER sell a customer both O2 sensors just because one is junk - replace the bad one, and that's it. Especially since it really isn't saving you any time to do both now - aside from jacking up the car, there are no parts you need to remove to do one sensor that make it any easier to get at the second one, so you aren't saving yourself any work. Anyway, rant over.

One more thing i don't think i saw mentioned - you said your failed spark plug had carbon tracking on the porcelain, right? Then that also means that the spark plug boot on the wire will have tracks burned in it, so you should also replace that wire. That's the way we do it in the shop as well - if a plug has carbon tracking, replace it and the boot.
 

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When it comes to 130k miles old O2 sensors... you replace 1 bank with a brand new sensor, and the other bank is still running off the old lazy sensor. Replacing only 1 in this case is like replacing only your left shoe because it has a hole in the toe, while the right shoe is only worn, but still intact. My personal opinion and preference is to replace both old sensors at the same time. I like to know that both banks are operating under the same parameters. Just preventative maintenance.

Now in the case of my '01 Dakota.... I've been driving around for 3 years with a failed downstream O2 sensor... the heater circuit is fried inside the sensor. It doesn't affect drivability or fuel consumption, so I haven't bothered to replace it. While the truck in sitting on jack stands under my carport while I install a new front suspension (worn out at 100k), I will finally replace the 100k downstream sensors and eliminate the annoying orange light on my dash.
 

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hi,

In NC if the CEL is on, the car will fail NC State Emissions inspection.
On older vehicles there is no emission testing so no problem with the CEL.

So depending on the State Emissions Inspection rules for you location you
may not need to replace the sensor(s).

regards,

James
 

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Seriously? The thread IS four years old and the original link was undoubtedly to a click bait site.
 
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