Changing out my ignition coils on my 2007 Lexus GS450H because I’m having misfire issues. I took a few of them out and saw some reddish brown debris on one of them. Is this indication of a bad coil?
That reddish-brown debris is a very common sight on Lexus/Toyota ignition coils, and while it isn’t necessarily a sign that the coil’s internal electronics have failed, it is a significant clue to your misfire.
Here is a breakdown of what that debris likely is and what it tells you about your misfire:
1. What is the debris?
In most cases, reddish-brown “dust” or debris on the ignition coil boot (the rubber part) is Corona Stain or Rusted Flashover.
Corona Stain: This is a light brown/tan discoloration on the ceramic part of the spark plug or the rubber boot. It’s caused by the high voltage of the ignition system attracting dirt and oil particles in the air. By itself, it is often considered normal.
Iron Oxide/Rust: If the debris is more “crusty” or gritty, it often indicates that moisture has reached the spark plug well. On the GS450H, this is common if the spark plug tube seals in the valve cover are leaking slightly or if moisture/condensation has been trapped in the tube over time.
2. Why it causes a misfire
The debris itself isn’t the “failure,” but it creates a path for the electricity.
Arcing (Flashover): High-voltage electricity always looks for the path of least resistance to ground. The reddish debris (especially if it contains metallic iron oxide from rust) can act as a bridge. Instead of the spark jumping the gap at the bottom of the spark plug to ignite the fuel, it “shorts out” by jumping down the side of the plug through that debris.
Trace Lines: Look closely at the white ceramic of the spark plug and the inside of the rubber coil boot. If you see thin, black “lightning” lines (carbon tracks), that confirms the electricity is escaping.
3. Is the coil “Bad”?
Not necessarily. Many times, the coil is electronically fine, but the rubber boot is compromised.
Check the boot: If the rubber is brittle, cracked, or heavily stained with that debris, it can no longer insulate the voltage.
The “Swap Test”: To be sure, take the coil with the debris and move it to a different cylinder (e.g., move it from Cylinder 1 to Cylinder 2). Use an OBD-II scanner to see if the misfire “follows” the coil to the new cylinder. If it does, the coil (or its boot) is definitely the problem.
4. Recommendation for your GS450H
Since you already have the coils out:
Replace the Spark Plugs: If you see debris on the coil, the spark plug in that hole is almost certainly fouled or has “corona” buildup. Misfires on 2007-era Lexus hybrids are frequently just worn-out plugs (standard interval is 60k-100k miles).
Clean the Spark Plug Well: Use a vacuum or compressed air to get all that reddish debris out of the hole before you remove the spark plug so it doesn’t fall into the engine.
Inspect the Tube Seals: Look for oil in the bottom of the tube. If there’s oil mixed with that red dust, your valve cover gasket/tube seals are leaking and will eventually kill your new coils too.
Use Dielectric Grease: When installing the new coils, apply a small dab of dielectric grease inside the tip of the rubber boot. This helps prevent future moisture intrusion and arcing.
Don’t let a faulty coil or a leaking gasket compromise your vehicle’s safety and power. Get the professional parts you need today.
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