Black Spark Plugs Is That An O2 Sensor Going Bad

Posted in Ignition Systems

1986 RS Camaro? We have checked and replace just about everything, First the converter would glow red, so we put a new one on it, still after a few mins it would start to glow red, so we check the plugs, drivers side are perfect, passenger side were covered in sut. So we changed the computer, did nothing, check the vacuum they were fine, the compression was good, and the gas pressure was normal. What’s wrong with it?
ok here’s what i have done to the car. We changed the converter, checked compression, and gas and all that, changed the computer. And the injectors were good. The car would run for a few seconds and then quit. But when i changed the convertor it would run but you could tell something was still wrong, so we check the distributer cap it was fine. Then we started checking the injectors and they were fine and then it just quit running. So i figured it was the battery, i have it on charge now and will check when i get home. I have not checked every Vacuum line in the engine, it’s a 2.8 V6 by the way. The Exhaust is dual with one convertor and muffler connecting in the back. We checked the vacuum lines that were (easy to get to) upfront, I am not a mechanic so the names i am really clueless. I am getting ready to take it to another shop and let them go over it with a fine tooth comb. Any other idea’s?

There are 11 Answers for "Black Spark Plugs Is That An O2 Sensor Going Bad"

    1. Roger says:

      I’m not positive about this, but a lot of carbon build-up on the spark plugs may be a result of the air/fuel mixture being too rich with fuel. You may want to take it to a shop that can adjust that for optimal performance.

    2. southernvixin00 says:

      you will know when it’s your o2 sensor, you car will run like crap, and suck up all your gas. Spark plugs will be black if it’s been a long time since your last tune-up

    3. gary o says:

      Must be getting a lot of excess fuel in the converter for it to glow. If vacuum was 18-20 at idle then mechanicals are OK and assuming timing is OK then check EGR system.

    4. IronButt61 says:

      Black soot usually means it’s running rich.
      This “can” happen if the O2 sensor is bad, sending incorrect info to the computer telling it to send more fuel to the mix, but it’s no guarantee.

    5. mark j says:

      Cam sensor for that bank of lifters if all four plugs are covered.
      stuck lifter if only one or two are bad.

    6. flh_ryder says:

      how many converters does your vehicle have?….it may also have converters in the crossover pipe system that come off your exhaust manifolds….not to say that this is the problem.
      If the converter is still glowing red after replacement it could mean that you have a quantity of unburned fuel reaching the converter causing the overheat situation…what bothers me is you didn’t say anything about a emissions light being on….and if it’s doing what you say it is…the light really should be on….does this vehicle have throttle body injection or is it ported?….the injectors may be hanging open too long or bleeding down into the right bank….there are lots of possibilities here.

    7. Ronk W says:

      An Oxygen Sensor by itself will not cause the problem… you didn’t list what you have done exactly…

      telling us that will eliminate some things…

      so you’re asking us to fly by seat of the pants and for some people to guess at your problem….

      vs give you an exact dead on diagnoisis…

      since the problem exists on only one side of engine it has to be something like a very bad vaccum leak causing it only to load fuel on that side…

      because of input put to the computer that the computer feeds back to the injectors on that side to correct

      could be the brake booster is bad for the power brakes and its hooked into the manifold that feeds that side of engine…

      (which wouild lean out only that side of engine or 4 cylinderrs on a V8 and the computer would sense that thru oxygen sensor and try to richen to correct for the increased air which in turn would fuel foul plugs)

      if the engine has 2 separate fuel rails and pressure reguulators in the rails the one on that side is bad…

      or when it was apart checking injectors the rail may have gotten pinched or crimped there by increasing the fuel pressure going to the injectors on that side

      once problem is found you will need to replace that oxygen sensor because it will be plugged and not replacing it will cause a slight engine miss

      be aware many givign advice here do not repair cars for a living hence they may not know what they are talking about too..


      P.S. I will revise this answer if you give more input as to what you have had done or haven’t too..

    8. Stampy Skunk says:

      Fuel injectors…… running rich …..

    9. the bear facts says:

      This is a hard one to answer,it is something that is only effecting one bank,the catalytic converter only glows if there is an excessive amount of fuel going into it.Does it have dual exhaust and is it seperate for both sides,I would check the exhaust system for blockage on the side effected.
      As for some of the other answers you recieved the EGR valve would effect all cylinders not just 4 also it would not make the CAT glow anyway,I would look for something that only effects one side,start with the exhaust and work your way forwards.

    10. michael081278 says:

      Ok, first of all which cylinders were the spark plugs black?

      If just a few of them, then you will probably have a problem in your ignition system somewhere.

      If all your plugs are black, then you have an extremely rich condition. I would be willing to bet that a sensor is causing the computer to flood the engine out. The most common causes of this is:

      -Engine Coolant Temp Sensor.
      (If this sensor goes bad, the computer doesn’t know when to go into closed loop and will remain enrichening the engine thinking it needs it for a cold start.

      -MAP sensor
      (If this sensor goes bad, the computer doesn’t know how dense the air is and usually either leans the car out or floods it.)

      -Oxygen Sensor
      (If this sensor goes bad, and gives the computer a false reading that the car is running full lean, the computer will try to compensate for it and dump a ton a fuel into the engine til it notices a change.)

      These are the most common on a vehicle this old. I would start there.
      Good luck and I hope this helps!

    11. Nomadd says:

      Check the vacuum line to the fuel pressure regulator. If it’s bad it will be leaking gas into the intake manifold, making the engine run extremely rich.