When a Yamaha misses on one cylinder, you are left with a question that sensors cannot answer: is it the coil or is it the injector. The component test in the app lets you drive each of them separately, cylinder by cylinder, which turns a guess into a comparison. How it plays out depends on the engine, so here is what you actually have in front of you.
What the engine gives you to test
On the three-cylinder machines, meaning the GP1300R of 2003 to 2008 and the TR-1 models (the VX from 2015, the EX, the SuperJet and the JetBlaster), there are three coils, three injectors and the fuel pump, so seven components in all. On four-cylinder models where every cylinder has its own coil, the same list adds up to nine.
The early FX models are the exception. The FX140 and FX1000 of 2002 to 2005, and the FX1000(A), FX1100 and FX HO MR-1 up to 2008, have only two coils, and each fires two cylinders in a pair, 1 and 4 together and 2 and 3 together. They still have four injectors. A dead coil there takes out two cylinders at once, which people sometimes read as two separate problems. The app only shows the components your model actually has.
How to compare
The method that works is to run the same test on every cylinder and look for the odd one out. A coil or injector that behaves differently from its neighbours stands out far more clearly than any single result read in isolation. Do the coils first, then the injectors. Write down which cylinder reacted and which did not, so that you still have it after the second round.
If one coil looks weak, swap it with the coil of a neighbouring cylinder and test again. When the weak behaviour moves to the new cylinder, the coil is the culprit. If it stays where it was, the problem lies in the wiring, the plug or the cylinder itself. The same swap logic works for injectors, though on some engines access makes that a bigger job.
Where the test ends
A component test shows that a part is being driven and that it responds. It does not show the quality of the spark under compression or the spray pattern of an injector. The fuel pump test is the clearest example, because it only tells you that the pump runs. A pump that runs but delivers too little will pass, and you would only notice it as a ski that stumbles under load.
The test also does not see the things around the part: a corroded plug, a bad ground, worn spark plugs or low compression on one cylinder. If a cylinder fails the test after you have eliminated the coil and the injector, the plug and the compression are the next suspects, and neither of them is something the electronics can report. Careful with the plugs, since seized threads are a known problem.
Safety
You are working next to the fuel system, so make sure the area is well ventilated and free of anything that can ignite fuel vapour. Never run the engine on land without water supply to the pump.
The Yamaha version of the M-JET Diagnostic covers these tests on its 37 supported four-stroke models. The page about the component and actuator test lists what each model offers, and checking the ignition coil and injector walks through the comparison step by step.
