Coil or Injector: Testing Each Cylinder on a Yamaha Outboard

The engine shakes at idle, runs rough under load and sounds like it's down a cylinder. The question is almost always the same: no spark or no fuel. With M-JET DIAGNOSTIC you can, depending on the engine, fire each ignition coil and each injector individually with an actuator test instead of throwing parts at it.

What can be activated on which engines

• F20 to F100: single coils and injectors or pairs, such as coils 1 and 4 together, depending on the ECU.
• F115 to F150: each of the four cylinders individually or in pairs, depending on the ECU.
• F175 to F250: up to six coils and six injectors, on some ECUs as pairs 1 and 4, 2 and 5, 3 and 6.
• F275 to F450: up to eight coils and eight injectors individually. The fault memory also has an irregular signal entry for each injector.
• HPDI Z series: six coils and six injectors, plus a firing state for every cylinder in live data.

How to run the actuator test

With the engine off, activate the injectors one at a time and listen with a screwdriver or a mechanic's stethoscope on the injector body. Each one should click evenly. If one stays quiet, check the connector, wiring and resistance. For the coils, pull the plug wire or boot, fit a spark tester and let the app pulse the coil. If one coil gives no spark while the others fire cleanly, you have your suspect. Keep fuel vapor well away while you do this and don't keep cycling the injectors, or fuel will pool in the cylinder.

The swap trick confirms it

If both tests pass and the cylinder still misfires, swap the ignition coil with a neighboring cylinder. If the misfire follows the coil, it's the coil. If it stays put, look at the spark plug and the injector. On the HPDI Z series, the firing state in live data shows you right away which cylinder is dropping out. On F275 to F450, the check procedure for an injector entry also points to the injector driver unit, besides the wiring and the actuator test.

When spark and injector both check out

Then it's usually mechanical. A compression test shows burned valves, tight valve clearance or broken rings. An intake air leak entry can point to a leaking intake manifold gasket that leans out just one cylinder. Dirty injectors often click normally in the test but spray poorly. A shop checks the spray pattern on a flow bench. So check plugs and coils first, then injectors, then compression.

Related topics

• Test Yamaha Outboard Coils, Injectors and Fuel Pumps One at a Time
• Yamaha Outboard Rough Idle or Stalling: Checking the ISC and Relearning Idle
• Yamaha Outboard Won't Start: Checking Kill Switch, Shift, Pulser Coil and Battery
• All Yamaha outboard diagnostics topics

Everything runs via app over Bluetooth, for Yamaha outboards with control unit generations from 2003. Learn more about the M-JET DIAGNOSTIC for Yamaha WaveRunner & Outboard.