Test Yamaha Outboard Coils, Injectors and Fuel Pumps One at a Time

One cylinder drops out, the engine shakes at idle, and you can't tell whether it's the coil or the injector. Instead of throwing parts at it, you use M-JET DIAGNOSTIC to activate each component on its own. The ECU then fires one coil, one injector or the pump on command, and you listen or measure to see whether it responds. The tests run with the engine stopped.

Which actuator tests are available

• Ignition coils individually or in pairs, on some four-cylinders cylinders 1 and 4 together
• Injectors individually or in pairs, up to eight on a V8
• Electric fuel pump and low-pressure pump
• ISC valve for idle air
• OCV for variable cam timing, on V engines separately for each bank
• on big engines in the F275 to F450 class also the vapor separator tank (VST) pumps, the direct injection pumps, a fuel system air purge and a function to reduce injection pressure
• on the HPDI Z series the oil plunger pump

How many tests your engine has

Depending on the ECU, you get between 4 and 25 actuator tests. The F20 to F100 class offers 4 to 8, F115 to F150 has 6 to 11, F175 to F250 has 9 to 16 and F275 to F450 has 16 to 25. The HPDI Z series engines have 14, one coil and one injector for each of the six cylinders plus the fuel pump and oil pump. The app only shows the tests your ECU knows.

Separating ignition from fuel

• Read the fault memory first. If there's an entry for a specific injector or the pulser coil, you already have a direction
• Fire the coil on the suspect cylinder and check it with a spark tester
• Fire the injector on the same cylinder. A crisp click tells you the driver, the wiring and the injector solenoid are working
• Run the fuel pump and listen for it to start
• Only once everything works electrically do you move on to spark plugs, compression and fuel

A real-world example

A four-cylinder shakes at idle and the fault memory is empty. The actuator test shows every coil and injector responding. That takes the ECU's control side out of the picture, and you move on to plugs, plug boots and compression. If one injector doesn't respond, on the other hand, measure at its connector before you order a new one. Often it's the wiring, not the part.

What an actuator test doesn't prove

An actuator test checks whether the part responds to the command. It says nothing about whether an injector atomizes cleanly or is partly gummed up, whether the plug is fouled or whether the pump makes full pressure. On the direct-injected engines you at least get fuel pressure as a live value. A compression test is still a hands-on job, same as looking at plug wires and boots, which like to corrode in salt water.

Related topics

• Coil or Injector: Testing Each Cylinder on a Yamaha Outboard
• Yamaha Outboard Won't Start: Checking Kill Switch, Shift, Pulser Coil and Battery
• Read Yamaha Outboard Engine Hours by RPM Range
• 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.