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P0171 Oxygen sensor?

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  • P0171 Oxygen sensor?

    2000 Ford Contour Bi-Fuel. I have a code P0171 and the fuel economy is horrible. Have had people searching for vaccuum leaks multiple times and never really nailed it. Is it time to change the O2 Sensor?

    I just removed the heat shield and I've let some Seafoam Deep Creep on the sensor to penetrate into the threads.

    Also have a U1262 code. I think that is probably from my failing CompuValve. I think I have a precudre printed up somewhere to do a reset.

    The goal is to get this car to pass emissions inspection. Otherwise, I'm donating to Cars for Vets for the tax write-off.

  • #2
    yes P0171 can be an indication of a bad O2 sensor. How old is it and how many miles? If you are certain there are no vacuum leaks then its most likely worth changing the sensor.
    - 12 Focus SE
    - 95 Mystique LS <-sold
    - 99 Contour SE Sport <- traded in 2/13
    - 99 Contour SeVT <- 3L/NPG Turbo
    - 2k Contour SVT - #2137

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    • #3
      It's a 2000 Contour - so maybe 17 years old and over 146K miles. I already picked up a sensor.

      The dealer claimed to fix the vaccuum leaks, a third party mechanic wouldn't/couldn't get the O2 sensor out for risk of damaging it. Getting that heat shield off was a real pain, but now that the sensor is exposed, I might be able to get at it with a wrench.

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      • #4
        O2 sensors have about a 60K mile useful life, less if the engine is burning oil, and as they age, they start switching more slowly and report lean back to the ECU, so the ECU keeps adding fuel pretty much across the board, and fuel economy goes in the shi**er.
        I collect Ford's Red-headed step children.
        1985 SVO Mustang (turbocharged track rat)
        1989 Taurus SHO (supercharged track rat)
        1999 SVT Contour (Sedanus-Grocerygetter-Rapidus)
        2008 Mercury Milan Premier (Comfy boat)

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        • #5
          I'm hoping this O2 sensor (top, at the manifold) does the trick. I dread having to find and wrestle the one under the car somewhere.

          Just need to get this car to pass for another year or two....

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          • #6
            Yeah, you want to replace the upstream (pre-cat) sensor first, that's the one that the ECU uses to monitor and maintain engine air/fuel ratio. The post cat O2 sensor is used to monitor the cat performance, it wouldn't hurt to replace that one as well, but they tend to last a lot longer as they're further from the high temps of the engine exhaust gas. The post-cat sensor is usually pretty easy to find, but you will have to go under the car.
            I collect Ford's Red-headed step children.
            1985 SVO Mustang (turbocharged track rat)
            1989 Taurus SHO (supercharged track rat)
            1999 SVT Contour (Sedanus-Grocerygetter-Rapidus)
            2008 Mercury Milan Premier (Comfy boat)

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            • #7
              60K!!?? I think I have at least one car with the same O2 sensor for over 240K miles! (2000 Nissan Altima) I think I changed it at 250K miles for a check engine light years ago.

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              • #8
                60-75K used to be the recommended change duration but it's to sell parts of course. If the car is kept in good shape tune wise they can go easily to 150K+, I have 3 doing over that right now. They of course might get a bit better mileage with new sensors but they seem to run fine.

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                • #9
                  I just tried to remove the sensor last night and used one of those cheap harbor freight O2 sensor sockets. I rounded off the edges a little and decided to stop. I think I'l save this toward the weekend. I have a propane torch, someone said I might get away with heating it for a good 10 minutes, then give it a good soaking with Seafoam Deep Creep and PBBlaster and let it cool down for a day.

                  I'll ditch the HF O2 sensor tool and try to get a 7/8 box wrench on it and tap it with a hammer. Suprisingly, I do not see any rust on the sensor.

                  If that don't work, maybe vice grips and a hammer?

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                  • #10
                    I got a 22 MM deep impact socket (6 point), the 7/8 deep socket at Home Depot was a 12 point (didn't want that!). Hit it with PB Blaster the night before, and the night before that.

                    It came off with moderate force. I noticed a curl of metal coming off the sensor as it twisted out of the manifold bung.

                    I inspected the sensor and the thread was intact, but the edges were shaved off.

                    I then tried to twist the new one in. It won't go in!!!!! @#$@Q$#Q!

                    The threads in the bung appear to be uniform and undamaged, but rusty.

                    The threads on the old O2 sensor are shiny as they have had metal shaved off them. Possible the original installer of the O2 sensor had cross-threaded it and just forced it in there. Or the manifold threads are wonky.

                    I read somewhere to put the new sensor in the freezer and run the engine for a while - theory is to get the sensor to contract and the manifold hole to expand. I would think the manifold metal with expand into the hole, but I figured I'd give it a shot.

                    Froze the O2 sensor in my freezer overnight and ran the engine tonight for ten minutes - it was pretty hot and hard to maneuver in there!

                    No success. Still just kinda spins without catching. I tried brushing out the manifold hole/socket with a small brass brush. Still no success.

                    Wondering if I should try spinning a little sandpaper in the hole and around the O2 sensor? Sure, I'll rub off all the anti-seize on the threads, but I don't care. I just plan to run this car for another two years if possible before getting rid of it.

                    Another option is to ask around and see if anyone has an O2 sensor tap to expand the hole a bit. I have access to the auto hobby shop at Fort Belvoir. Maybe see if they have one.

                    btw. the old sensor goes back in easily. I was able to turn it in by hand and then just tightened a little bit the HF O2 sensor tool.

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                    • #11
                      I'm going to the auto parts store at lunch to pick up a Oxygen Sensor Thread Chaser. Supposed to work well on cleaning out the threads and helping to realign them. Will do that before using a tap.

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                      • #12
                        Find one of these. Absolutely amazing.
                        The we purchased specifically had Cougar/Contour listed on it.
                        Shop for OEM Oxygen sensor socket 27162 with confidence at AutoZone.com. Parts are just part of what we do. Get yours online today and pick up in store.
                        1999 Cougar V6 Spruce Green-Awaiting Transplant
                        1999 Cougar V6 Silver Frost
                        NorCal NECO

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                        • #13
                          Originally posted by LostRacer View Post
                          Find one of these. Absolutely amazing.
                          The we purchased specifically had Cougar/Contour listed on it.
                          That Autozone O2 sensor wrench is pretty cool, never seen one of those before, and it even specifically mentions hard to reach sensors on Contours.

                          I have one of the split sockets, and they work OK unless a sensor is really tight, then they tend to spread if you have to apply a lot of torque to break the sensor loose. I think I ended up using a box wrench to get the Contour's rear upstream sensor loose, and it was a real struggle.

                          For that thread chaser, make sure you use lubricant on it, oil or anti-seize, and put some anti-seize on the new sensor's threads so it will be less likely to seize in place. Don't get anti-seize on the sensor itself, it often contains some Lead which will poison the sensor, just coat the threads to be nice to the poor bastard who owns the car after you.
                          I collect Ford's Red-headed step children.
                          1985 SVO Mustang (turbocharged track rat)
                          1989 Taurus SHO (supercharged track rat)
                          1999 SVT Contour (Sedanus-Grocerygetter-Rapidus)
                          2008 Mercury Milan Premier (Comfy boat)

                          Comment


                          • #14
                            Originally posted by LostRacer View Post
                            Find one of these. Absolutely amazing.
                            The we purchased specifically had Cougar/Contour listed on it.
                            Aaawwww! Coulda used that three weeks ago!

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