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Thread: Spark Plug check

  1. #1
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    Spark Plug check

    So I took out my spark plugs to replace them today, does the condition of these say anything about my engine? Keep in mind I'm sure the past owner never replaced them.

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  2. #2
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    Carbon fouling, your running rich. Smoke test the vacuum system for leaks. Replace the oxygen sensor.
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  3. #3
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    Quote Originally Posted by Eric93se View Post
    Carbon fouling, your running rich. Smoke test the vacuum system for leaks. Replace the oxygen sensor.
    I just replaced all the broken vacuum lines, thanks for letting me know it's running rich!

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  4. #4
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    Carbon coated = rich yes. But the oil on the plugs is a V cover seal leak but it also got into the cylinder on one and you were burning oil. or was the plug a bit looses? Plug tips look clean, they are not copper because it looks to uniform and pointy, Iridium? They can go for 100,000 miles. Not OEM in 94

  5. #5
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    Quote Originally Posted by gc325is View Post
    Carbon coated = rich yes. But the oil on the plugs is a V cover seal leak but it also got into the cylinder on one and you were burning oil. or was the plug a bit looses? Plug tips look clean, they are not copper because it looks to uniform and pointy, Iridium? They can go for 100,000 miles. Not OEM in 94
    The plug was a bit loose but if you say it could be the seal I'll likely just replace the seal to be safe. They are iridium though and they probably have some life in them but I'm going to replace them just to be safe. Thanks for the information!

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  6. #6
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    Valve cover seal leak is also a vacuum leak. It is also the reason why the plugs are coated outside with oil.

    The one plug thats not all black means it was burning different than the rest. Hopefully it was a loose plus and oil seeped into the plug, not a internal oil seal on a valve or piston. As eric said your O2 sensor may not be working and the CAT could be dead. Cylinders may be filled with carbon too.

    You never said how the car was running. If you want to know how well the engine is there are other tests you can do. Cylinder compression test, oil inspection, and since you have 4 plugs a head gasket inspection and other specific 318 item.

  7. #7
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    I agree you should do the valve cover gasket, but it's not likely the cylinder was drawing in oil (to burn), it's just oil seeping by the valve cover gasket. Be sure to read any guides on how to properly do the valve cover gasket for your engine there maybe the need to put a few strategic dabs of silicon sealant. I forgot one time and it did leak right where it's supposed to get some RTV silicone.
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  8. #8
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    No Just running Rich but also some oil burn and introduction of outside air going on, some plugs are grayish. Check for more leaks, grab a cheap $50 smoke party fog machine from ebay, great for finding leaks, likely the rocker cover leak..
    "So we've come to the conclusion that BMW just has parts laying around they decide to throw on cars for no reason."

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  9. #9
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    Oil doesn't seep past the plugs into the cylinders unless they are half way out and the engine isn't running. Think about it, gravity vs 150+psi, which way is the oil going flow?

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  10. #10
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    Oil doesn't seep past the plugs into the cylinders unless they are half way out and the engine isn't running.

    However, A Hot engine that cools down has lots of pressure to suck in oil from a loose plug

    https://www.youtube.com/watch?v=Uy-SN5j1ogk

    I just pulled my Bosh iridiums. They look almost as bad as yours. Only ~25,000 miles. I was also reading a higher impedance on a few 11K ohms vs 5K. I am thinking the oil could be fouling them then causing the plugs to be damaged and cause a resistance change? Which then leads to a miss fire and poor emissions.

    Or I'm just running rich because that VC is leaking again

    PC160557a.jpg


    PS: SMOG guy said oil burning is the biggest cause for a dead CAT.
    Last edited by gc325is; 12-29-2017 at 01:52 PM.

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