Rough Idle and Shaking? How to Find a Misfiring Cylinder in Minutes by Professional Mehcanic
About this video
Engine misfire diagnosis without guessing. In this video our mechanic shows how to find a misfiring cylinder using a scan tool, reads live misfire counter data, graphs it on the scanner, then pulls the faulty spark plug to confirm the diagnosis.
Most people replace all the plugs and coils and hope the problem goes away. This is how you find the exact cylinder first, then fix only what is actually bad.
Symptoms of an engine misfire:
Check engine light flashing or steady
Rough idle, shaking or vibration at a stop
Loss of power and hesitation on acceleration
Poor fuel economy
Engine stumble or surging at cruise
Smell of raw fuel from the exhaust
Hard starting or long crank
Misfire fault codes covered:
P0300 Random or multiple cylinder misfire
P0301 through P0312 Cylinder specific misfire
P0171 and P0174 System too lean
P0351 through P0358 Ignition coil circuit malfunction
P0420 Catalyst efficiency below threshold, often caused by a long running misfire
Common causes of an engine misfire:
Worn or fouled spark plugs
Failing ignition coil or coil pack
Bad plug wires on older vehicles
Clogged or leaking fuel injector
Vacuum leak
Low compression, burned valve or worn rings
Failing crankshaft or camshaft position sensor
Carbon buildup on direct injection intake valves
Restricted exhaust or failed catalytic converter
A flashing check engine light means the misfire is severe enough to damage the catalytic converter. Stop driving and diagnose it before the repair gets much more expensive.
This procedure applies to nearly any OBD2 vehicle from 1996 to present, including Toyota, Honda, Ford, Chevrolet, GMC, Dodge, Ram, Jeep, Chrysler, Nissan, Hyundai, Kia, Subaru, Mazda, Volkswagen, Audi, BMW, Mercedes-Benz, Volvo, Lexus, Acura and Infiniti. The misfire counter logic works the same on four cylinder, V6 and V8 engines, turbocharged or naturally aspirated, coil on plug or coil pack ignition.
Scan tool used: YOUCANIC UCAN-II Pro, a bidirectional scanner with live data graphing, misfire counters and full system diagnostics.
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For more free repair guides, wiring diagrams, fault code lookups and professional diagnostic scan tools, visit https://www.youcanic.com