Engine Misfire Symptoms
A misfire is a cylinder failing to burn its fuel. The car shakes, loses power, and dumps raw fuel into the converter, which is why a flashing light means stop.
What it feels like
- A rhythmic shake that speeds up with the engine
- The car surges and hesitates under light throttle
- A sulfur or raw fuel smell from the tailpipe
- Fuel economy dropping by several miles per gallon
Codes that usually produce this
Check these first, in this order
Free checks first. Nothing here costs money except the fuel you burn.
- 1
Read per-cylinder misfire counters with the scanner at idle, then again at 2500 rpm.
What you'll seeOne cylinder counting up. A misfire only at higher rpm points at ignition or fuel, not compression.
- 2
Swap the suspect coil with a neighbor along the top of the valve cover, then drive 20 miles.
What you'll seeThe counter either moves with the coil or stays put. Both answers cut the suspect list in half.
- 3
Pull the suspect plug and compare it against a neighbor from a healthy cylinder.
What you'll seeA black wet tip or a worn gap on the suspect plug confirms that cylinder.
Stop and get it looked at if
- The check engine light flashes at any point.
- The engine shakes hard enough that the car rocks at idle.
- You smell raw fuel at the tailpipe.