What exactly are the symptoms of bad O2 sensors?

Discussion in '1994 - 1995 Specific Tech' started by 99FiveOh, Apr 16, 2010.


  1. 99FiveOh

    99FiveOh Advanced Member

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    Here's my issue. I've been battling a shuddering/backfire/hesitation problem for almost half a year now.

    Fast forward to now. I acquired another car that I bought for parts originally, but decided to restore it since it was in much better shape than my old car.

    I had to borrow quite a few parts as well as the fuse panel/headlight harness to get the car back on the road. It seems whatever sickness my other car had this one has it now.

    For a while I've been blaming the dizzy for these problems, but I've been through no less than 5 or 6 of them in the past year. I'm thinking they are the cause because a couple times when I replaced the dizzy the problem was solved for a while.

    Well, this car has the problem with the dizzy that was in it as well as mine so since the symptom did not change upon switching it out, I'm going to rule it out as a culprit.

    Since my MAF was used from the other car, I went ahead and reinstalled the MAF that came with the new car, but the symptoms were unchanged. The only thing left would be the 02 sensors in the same H pipe that I carried over to the new car. Could 02 sensors really cause that much of a problem with drivability? I'm about at wits end with this! The guy who had the car before me said it ran fine and had none of the symptoms I've described so it has to be something I used from my car. All the rest of the sensors on the engine are the same ones that came with it.

    Sorry this is so long but I would really like to have a nice running car again!! :shrug:
     
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  2. 99FiveOh

    99FiveOh Advanced Member

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    I wanted to add that the check engine light comes on briefly at times and goes out. Also, if I go to WOT the problem seems to clear up on it's own and the car accelerates fine. I mention that my method of blocking the egr is the same as I did from the old car. I used a penny both on the header and the EGR valve itself.
     
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  3. GTA_V6_Mustang

    GTA_V6_Mustang Active Member

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    a bad o2 can TOTALLY cause that problem. Have you tried pulling a code yet? Also a TPS can cause that too.
     
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  4. 99FiveOh

    99FiveOh Advanced Member

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    The TPS wasn't carried over. I pulled codes in the old car and got all kinds of stuff. Can't remember exactly what but it was saying things like fuel pump circuit failure, spout connector circuit failure, lean condition.
     
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  5. toyman

    toyman SN Certified Technician

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    The O2's provide feedback to the ECU to manage fuel/air under normal throttle position (closed loop). However, at WOT the fuel/air is determined by the fuel map (open loop). O2's are important and have a finite life. If they have over 60k miles on them they should be replaced so as to ensure they are providing the ECU with the correct signal voltage.
     
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  6. BlackVert

    BlackVert Mustang Master

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    subscribing, as mine is having a shuddering issue right now.

    i had a plug wire that was too close to a header and was arcing. replacing that helped, but it still sumbles under medium/heavy throttle
     
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  7. 99FiveOh

    99FiveOh Advanced Member

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    I'm going to swap the O2's here in a bit and i'll post back with the results. I'm also going to a shop with a nice code scanner to find out once and for all what the CE light has to say!
     
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  8. ProKiller

    ProKiller Founding Member

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    a bad o2 can dump tons of fuel into the car to keep it "healthy", basically keeping the engine from running too lean and killing itself. If it stumbles on itself when you accelerate, that very well could be your problem.
     
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  9. GTA_V6_Mustang

    GTA_V6_Mustang Active Member

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    I would start looking at the CCRM if your getting Fuel pump circuit failure
     
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  10. alleymad95GT

    alleymad95GT Member

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    Well, strictly responding to the title of the thread...

    Symptoms of a bad O2 sensor:

    Sudden decrease in fuel mileage. The air/fuel mixture of the vehicle becomes irregular, resulting in poor fuel economy.

    Engine missing is usually caused when a bad oxygen sensor affects the air/fuel mixture and engine combustion. It is more evident when the automobile is at idle and/or running at a very low speed.

    Engine pinging is another sign of a bad oxygen sensor, which is due to ignition of combustion gases at wrong times. A bad oxygen sensor either retards or advances the engine ignition timing, which can cause engine pinging.

    A vehicle with a bad oxygen sensor may run / idle roughly and/or irregularly.

    Increased exhaust emissions.

    Those are the things that a bad O2 sensor "can" do. Will it do all of them? Maybe, maybe not.
     
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  11. 99FiveOh

    99FiveOh Advanced Member

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    Well, I swapped in 2 extra O2's I had laying around and viola! Car runs and pulls smooth through the RPM range whether I'm hammering it or at part throttle.

    I took the car to my brother's shop and they put a Snap-On scanner on it. It had the ability to show what all the sensors were reading in real time and all the sensors were spot on. The tool didn't find anything out of the ordinary. It did say my thermactor system wasn't working in either bank, but that's because it's be ripped out and bypassed.

    So I guess thus far, the O2 sensors were the answer.
     
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  12. BlackVert

    BlackVert Mustang Master

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    that does it ... i'm getting new o2 sensors tomorrow.

    thanks
     
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  13. 99FiveOh

    99FiveOh Advanced Member

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    Well, been a couple days now and not one hickup!
     
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  14. GTA_V6_Mustang

    GTA_V6_Mustang Active Member

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    congrats on finding your problem.
     
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  15. 99FiveOh

    99FiveOh Advanced Member

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    Now I'm having another issue unfortunately. Since I got the car on the road I'm hearing what sounds like a out of round tire on the right rear of the car. However, I swapped the tires around and it still makes the same noise from the same side. It's like a Woh-woh-woh-woh-woh sound if that makes any sense.

    I'm going to jack the car up tomorrow and let the rear tires spin to see what I can find. I know I know, dangerous!
     
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  16. toyman

    toyman SN Certified Technician

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    Axle bearing is my guess. If the shaft is damaged an offset bearing is available. It will save you the cost of a new axle if that is the problem.
     
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  17. KamiKaziDK

    KamiKaziDK Member

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    any dirty sensor that has air blowing across it can cause your check engine light to flicker, so if it comes back at all..... Also, not sure about the woh woh woh being a bearing, they're usually a pretty obvious grinding sound. Is it making noise like the tread is separating? Trying to get a feel for the sound, I don't actually think that's it since you rotated the tires, lol
     
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  18. 99FiveOh

    99FiveOh Advanced Member

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    I didn't rotate the tires, I installed a set of used tires on the car and since I never drove the car before I put these tires on I can't be certain. The previous owner took his wheels/tires off before I picked it up. I will use the donut to figure out which tire it is. The tires do exhibit very choppy shoulders as if they were on the front end of a car and not rotated. I can't rotate because my wheels are staggered.
     
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  19. Adam95GT

    Adam95GT New Member

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    Crap i didnt look at this sooner... I had this same problem 3 years back... car would only act right under WOT. Woud hesitate and buck... i just figured if it was working under wot the 02s were not being taken in to consideration so they were my problem :D that was correct:nice:
     
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