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'93 Spirit, code 21

Discussion in 'EEK! - Every Extended-K Car' started by B10alia, Oct 2, 2017.

  1. B10alia

    B10alia Well-Known Member

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    Let me preface this by saying this is my sister's car, not mine, so some of the observations are secondhand.

    Check engine light came on last Wednesday, I was told about the issue on Friday before she left New Hampshire to come back home for the weekend. I said to drive slowly and that I would look at it when she got home. This drive apparently went fine. Car was showing a code 51 at this point- fuel mixture lean. I figured this was probably an O2 sensor issue, as the car had head gasket problems about a year ago and the sensor was not replaced. The "old" sensor looked to be the same as the replacement I bought, and didn't look like it had been in there more than 5 years or so. Installed the new sensor, changed the air filter, which was filthy, and went for a test drive. The car seemed fine, although I didn't really push it because of its age. CEL came on after about 10 minutes. However, the code 51 was now accompanied by a 21- O2 sensor lean. I drove back home, which was also uneventful despite the CEL being on. I reset the codes, but the code 21 returned. My sister tried to take the car back to NH today, but couldn't get on the highway. She said the car would not go faster than 45 and was shaking badly. She got back home on back roads and here the car sits. It's still showing 21, the 51 has not returned. The CEL does not come on until the car is warm, I was expecting that it would come on steadily on startup at this point.

    My current thoughts:
    -I damaged the new sensor on installation or it was defective from the factory (unlikely). I twisted the wires up pretty good installing it, and I'm worried that I pulled something loose internally. It didn't seem like it was enough to damage them and they didn't feel loose after I installed it.

    -Grounding issues. I forget which ground the O2 runs to, is it the one on the driver's side of the head?

    -Something else, like an exhaust leak in the downpipe between the manifold and the cat.

    I want to test the new sensor without removing it from the vehicle if possible. I think I remember seeing that they could be tested off-vehicle by heating with a blow torch and measuring across the output for a voltage change. What I'd like to do is warm the car up and then unplug the sensor and measure across the outputs, I should see an AC voltage here if the sensor is operating, and I expect it will probably be 7-8V ("RMS") on my cheapo multimeter. Is this a good test and are these reasonable expectations for the output? Any help's appreciated here!
     
    #1 B10alia, Oct 2, 2017
    Last edited: Oct 2, 2017
  2. ImperialCrown

    Level III Supporter

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    What brand O2 sensor is it? I have had problems with Bosch and 'universal' sensors. Mopar OEM is an NGK O2 sensor.
    Exhaust leaks can admit air on a negative pressure pulse and cause O2 sensor codes. Check fuel pressure and EGR.
    On-car testing, if the O2 signal wire is pegged at 0 volts or over 1 volt, then it is real. The warm O2 signal should be constantly switching high-low (about 0.8v to 0.2v, back and forth rapidly)
     
    Bob Lincoln likes this.
  3. AllanC

    AllanC Well-Known Member

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    You did not indicate the engine in the vehicle. 2.5 liter 4 cylinder or 3.0 liter V6?

    Did you use an OEM Mopar oxygen sensor? There are numerous comments on this forum that aftermarket oxygen sensors do NOT work well on Chrysler vehicles.

    See this schematic for location of oxygen sensor ground. The ground wire on the engine head is for the oxygen sensor heater circuit. If the sensor heater is not grounded properly then the oxygen sensor takes longer to get to operating temperature. That would mean the engine fuel management system remains longer in open loop operation. Fuel management uses fixed values for pulsing the fuel injector(s) and does NOT use a signal from the oxygen sensor to optimize fuel mixture.

    Oxygen Sensor.gif

    This is a likely suspect. If there is an exhaust leak and the oxygen sensor is seeing a lean condition all the time, the engine management system will make the air - fuel mixture extremely rich. An excessively rich mixture will cause the engine to chug and lack power.

    Try this test. Unplug the oxygen sensor and drive the car for 10 - 20 minutes and make sure the engine is at operating temperature. Does the engine still chug and lack power? Disconnecting the oxygen sensor makes the engine management system uses set values for air-fuel mixture. If the engine now has power then the exhaust leak is fooling the oxygen sensor and it is causing the engine fuel management to set an overly rich air-fuel mixture and hinder performance.

    If the engine still lacks power with the oxygen sensor unplugged, then I would suspect a plugged catalytic converter or other issue.


    This is a Y T video on how to test an oxygen sensor. I think it is better and safer to remove the sensor and test with a propane torch. An alternate way is to use a scan tool and monitor the signal from the oxygen sensor. It should fluctuate constantly with values less than 0.45 volt (lean condition) and greater than 0.45 volt (rich condition). One that does not have a fluctuating voltage signal is defective.


    View: https://www.youtube.com/watch?v=YL6xkOZxHZ0
     
  4. B10alia

    B10alia Well-Known Member

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    Took the car out this morning and drove it for a bit. I noticed that it seemed to have a hesitation on acceleration that got worse as the car warmed up. Once the CEL came on, moving beyond about 1/4 throttle just resulted in noise, with the car eventually picking up weakly, just before the point in pedal travel that would cause a downshift. I pulled over and unplugged the sensor, with no change. The car idles nicely and seems to run fine below about 1/4 throttle, but that's about all you get for power.

    This is a 2.5, and both oxygen sensors here are/were Bosch universal units. As I was trying to hook up test leads to at least see if the sensor was alive, I noticed that one of the pins on the (new) sensor connector had slipped back into the housing. This is on the grey wire, the sensor ground, which explains the issues. I don't know how this could have happened, I tried to push the pins out of the connector housing on the old sensor with the alligator clips and I couldn't; it looks like they should be positively retained in there unless improperly assembled or there was serious mechanical damage to the housing. I'm going to see if I can reinsert the wire with a pair of needlenose pliers later tonight, if not, the sensor will be going back to Advance as defective. I don't know if they stock the NGK version of this sensor there anymore, hopefully I can at least special order it.

    I'm kicking myself because I'm starting to think that the air filter might have caused the initial code 51. I also should have remembered that Bosch doesn't generally play well with Mopar (except maybe fuel pumps)!
     
  5. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Yeah, never use Bosch. I have two problems with them. The first is that the tip consists of just a few slits cut longitudinally;
    [​IMG]

    Whereas the Denso, NTK and other brands have 32 holes punched all around for faster and better sensing.
    [​IMG]

    The other issue is that the Bosch sensor body outside the manifold is about 1/8" longer than Denso and others, so that if you want to use an O2 socket to torque it to spec when installing, you crush the new harness down against the body with the socket, where the wires exit. And you have to snip the wires off when unscrewing it, because the hex portion of the socket won't fully reach the hex fitting on the body with the wires in place, and it will round off the sensor, making it near impossible to remove.
     
  6. neon98rt

    neon98rt Well-Known Member

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    cat convertor?
     
  7. B10alia

    B10alia Well-Known Member

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    Bob, that's exactly what I was talking about when I was saying the wires got twisted up, there was hardly any room for them in the socket.

    Surprise surprise, when I put the pin back where it belonged, everything worked fine, no codes, engine operates normally. To be fair, that type of connector has very little visibly different between "almost seated" and "seated" on the pins, but I'm still surprised that Bosch's QC would be this bad. Sure, they're probably buying the part from someone else and putting their stamp on it, but you would think they'd have better control over their suppliers.
     
  8. ImperialCrown

    Level III Supporter

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    Yes the catalytic converter is in the list of Possible Causes for this fault code.
    Fix the exhaust leak first.
    It will have to be determined if this is a fuel supply/pressure or exhaust flow or EFI electrical issue if the fault code remains.
    Look for this book:
    sd11172-1993-chrysler-22l-25l-tbi-sfi-flexfuel-service-manual-906399456.jpg
     
  9. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Had a code 21 failure once that was the heating element that failed on the O2 sensor. A week or two later the entire sensor failed, with code 51, bucking at speed, gas mileage dropping from 33 mpg highway to 25 to 21 before replacement.
     
  10. tomlct

    tomlct Member

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    No codes, but I have just changed an old O2 sensor on my 88 Aries 2.5. The one that came out was a Bosch - maybe 15-20 years old, thanks to what I read in this post, I chose Denso. I installed it last night. I am wondering if fuel economy mpg will improve a little. I think it is getting in the low 20's mixed driving.
     

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