You can drive, but do not put it off
The engine stumbles
The engine runs unevenly, the car shakes at idle, the exhaust note stutters. On the move the pull sags and consumption rises.
You can usually get home or to a garage, but every day of delay adds to the bill.
What to look at in the live data
- Misfire counters per cylinder. One counter ticking means that cylinder: plug, coil, injector. All of them ticking means a common cause: fuel, pressure, an air leak.
- Fuel trims. A large positive value together with misfires means air is bypassing the meter.
- Idle speed: hunting or steady.
Common causes, cheapest first
- Spark plugs — the cheapest and the most common cause.
- A coil or a HT lead on one cylinder.
- An air leak: a cracked intake boot, a dislodged hose.
- A clogged or leaking injector.
- Low compression in a cylinder — that one goes to a mechanic.
Codes that show up with this
P0300Random/multiple cylinder misfire detectedP0301Cylinder 1 misfire detectedP0302Cylinder 2 misfire detectedP0171System too lean (bank 1) — air leak or not enough fuel
These parameters in the reference
Engine RPMShort term fuel trim B1Long term fuel trim B1Mass air flow (MAF)Short term fuel trim B2Long term fuel trim B2O2 sensor B1S2 voltageFuel injection timing
Lamps that may be on
Do it step by step
Two counters and one swap answer the question a garage charges money for.How to find which cylinder is misfiring
A symptom is not a diagnosis. The same sign comes from a dozen different causes — the readings are what tell them apart, not the feeling.
How the app helps
CarScan shows exactly these readings live, remembers the highest and the lowest value of the trip, and puts them into a report you can hand to a mechanic.