Why spark plugs turn black

Causes may include a stuck choke, misadjusted or heavy carburetor float, a leaky injector or carburetor needle valve, low coil output or high resistance in your spark plug wires.

A dead oxygen sensor or coolant sensor also can be a cause of carbon fouling. A heavier, oily black deposit means that oil is being sucked down into the combustion chamber, likely via worn valve guides, guide seals or piston rings or a cracked piston.

Check for oil consumption problems including leaky valve cover gaskets, crankshaft end seals and oil pan gaskets. Although there are many different cases, if the insulation resistance between the center electrode and the shell is over 10 ohms, the engine can be started normally. If the insulation resistance drops to 0 ohms, the firing end is fouled by either wet or dry carbon.

When a spark plug overheats, deposits that have accumulated on the insulator tip melt and give the insulator tip a glazed or glossy appearance. Lead fouling usually appears as yellowish brown deposits on the insulator nose. This cannot be detected by a resistance tester at room temperature. Lead compounds combine at different temperatures. Breakage is usually caused by thermal expansion and thermal shock due to sudden heating or cooling.

From there you can select the best ones that are going to work for your vehicle. To check out the current prices of spark plugs on Amazon click here. Iridium vs Platinum Spark Plugs Article. If your fuel injectors are cracked or damaged they can cause more fuel to be injected into your engine cylinders that may not fully be burnt off during the combustion process that will cause your spark plugs to turn black and wet over time. If your fuel injector is cracked it can cause fuel from your fuel rails to be sent at a more rapid pace into the combustion chamber than is intended by the ECU of your engine.

When your cylinder would try to burn the excess fuel in the engine cylinders not all of that fuel would be burnt during the process and some would be left on the spark plugs, the rest would be sent out the exhaust port. Either way, having a leaky fuel injector is no good for your engine overall.

You basically just loosen the bolts on your fuel rail, remove the fuel rail, and then remove your fuel injectors. The number of fuel injectors that your car has will depend on the number of cylinders that your engine has.

Another thing that you can check if your spark plugs are black and wet is your engine air filter. If you have not replaced your engine air filter in a long time it can get plugged up with dirt and debris over time. If your engine is not able to suck in the air easily this can cause the engine to compensate with adding in more fuel to try to complete the combustion process.

You should check your air filter to see if it is dirty you would want to go ahead and replace it. Carbon deposits form naturally in the combustion chamber and, at high engine speeds, they can come off the piston and stick to the spark plug insulator. Being due to engine misfire, a natural cause, the easy fix is to simply change the spark plugs. Checking the spark plugs with carbon deposits or black soot on it can save you from having bigger issues with the ignition system over time.

If you see a black spark plug you can try to change its place with a good one. If the good spark plug also turns black, and the black one that you changed becomes cleaner than the problem lies in the cylinder head. But if nothing happens, than spark plugs can also be problematic.

Try buying a new set of plugs and repeating the above steps to clearly see if the cylinder head is responsible.