In depth article on how to read spark plugs - learn about how to read air / fuel mixture, timing and other tell-tale signs for optimum performance.. Learn how to read spark plugs by color, deposits, and wear patterns. Identify engine problems early and know when visual inspection isn't enough.
Then the plugs are pulled and inspected. After a change is made, a new set of plugs are installed (you cannot re-read used plugs accurately), and you repeat your test run. Ignition Timing. Spark Plug Reading June 18, 2026 HOME Reading Spark Plugs Thanks to Larry Meaux of Meaux Racing for providing this information and pictures. This is only valid if you shut-off the engine after the finish line then tow the car back to the pits where you remove the plugs for reading !! Or if you are on the dyno VALID ONLY for full load acceleration or steady state dyno tests Plugs are best.