Can a bad fuel injector cause a misfire on one cylinder?

Yes. A restricted, poorly spraying or leaking injector can cause a single-cylinder misfire. Rule out the coil and plug with a swap test and check compression first, then confirm with a flow test.

How do I know if the misfire is the coil or the injector?

Swap the coil to another cylinder. If the misfire moves, it is the coil. If it stays and spark plugs and compression are fine, the injector is the likely cause.

Misfire on One Cylinder: How to Tell If It's a Bad Fuel Injector

October 22, 2026

A code like P0301, P0302 or P0304 means the engine computer saw one specific cylinder misfire. The last digit is the cylinder number. Before you replace anything, work out whether that cylinder is missing spark, fuel or compression — because the fix is different for each.

Step 1: The swap test (spark)

Note which cylinder is misfiring.
Swap that cylinder's ignition coil with a neighbour's.
Clear codes and drive until the misfire returns.
If the misfire moved to the other cylinder, the coil is bad. If it stayed, swap the spark plugs the same way.

Step 2: Compression

If coil and plug didn't move the misfire, do a compression or leak-down test on that cylinder. Low compression points to valves, rings or a head gasket — no injector cleaning will fix that.

Step 3: The injector

Spark is good, compression is good, and the misfire stays on one cylinder? Now the injector is the prime suspect. On port-injected engines you can often swap that injector to another cylinder as well: if the misfire follows it, it's the injector.

Signs it's the injector rather than wiring:

The injector clicks (listen with a screwdriver or stethoscope) but the cylinder still misfires — likely restricted, poor spray or leaking.
No click at all — check the connector and wiring before condemning the injector.
Fuel smell, hard hot starts, or a plug that's wet and black — the injector may be dripping.

Step 4: Prove it with a flow test

Pull the whole set and have it flow tested. The flow sheet will show whether the suspect injector flows less than its neighbours, sprays poorly or leaks — and whether the others are drifting too. Often a cleaning brings the bad one back in line. If it doesn't, you replace only that injector.

Clean or replace?

Flow test result after cleaning	What to do
Flows in line with the set, good spray, no leak	Reinstall — cleaning fixed it
Still low or uneven after cleaning and reverse flush	Replace that injector
Leaks when closed	Replace that injector
Doesn't fire	Check wiring; if the injector is dead, replace it

Replacements: single fuel injectors or full injector sets.

What it costs

$15 per injector for ultrasonic cleaning and a flow test after cleaning, +$5 each for before numbers, reverse flush, or GDI/diesel. A 4-cylinder set is $60, and typical turnaround is 1–2 hours at 19320 65 Ave #214, Surrey. Book your cleaning.