Backfire Repair

Easy to understand step by step guide on how to repair an automotive engine backfire problem, steps are presented in order of popularity, this guide pertains to most vehicles.

Difficulty Scale: 5 of 10

Begin with the car on level ground, in park with the emergency brake set, engine cool.

Step 1 - If  the check engine or service engine soon light is illuminated visit - Read trouble codes

Check Engine Light

Step 2 - If moisture or resistance is present in the ignition system it can cause internal ignition crossfire which can allow the electrical discharge to transfer to an alternative cylinder which produces a backfire. Visit - Engine Tune Up

Engine Tune Up

Step 3 - If fuel system pressure drops, it causes a lean mixture which produces an engine backfire. Visit - Fuel system test Visit - Fuel filter replacement

Fuel System Pressure

Step 4 - If the engine is running rough it can produce a backfire. Visit - Engine Runs Rough

Misfiring Spark Plug

Step 5 - Faulty or inferior tune up parts it will cause the system to crossfire. Visit - Ignition system testing

Testing the Ignition System

Step 6 - A failed air intake boot can cause a backfire by altering the feedback voltage to the PCM. Visit - Air intake boot replacement

Air Intake Boot

Step 7 - If an air injection check valve or "gulp" valve fails it will allow extra air into the exhaust system causing backfiring, to check your systems valve, remove it to check air flow, air should only travel one direction. If air travels in both directions, the valve has failed and needs replacement. An air injection system designed to help dilute exhaust gases during engine power demands.

Step 8 - An engine vacuum leak can cause a lean mixture backfire. Visit - Vacuum Leak Detection

Vacuum Leak

Step 9 - Inspect the exhaust system for leaks such as broken welds or rust holes, small leaks in the exhaust system can take in cool air during deceleration causing a popping or backfiring in the exhaust system. Visit - Lean Mixture Repair

Exhaust Leak

Step 10 - On older engine's ignition timing is set at a specific degree in relationship to the crankshaft, if this timing becomes misadjusted it can cause low power, poor gas mileage, engine detonation (pinging) and backfiring. Visit - Set engine ignition timing

Helpful Information

A backfire occurs when there is an imbalance in the air to fuel ratio required for the engine to operate properly. If the fuel mixture is too lean (not enough fuel) will backfire through the intake, or too rich (too much fuel) will backfire out of the exhaust system. Some backfires can be extreme enough to cause damage to related components, anytime a backfire is observed diagnose and repair as needed.


Written by
Co-Founder and CEO of
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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