Based on your symptoms, I wouldn't take it to the dealer just yet. The combination of
no beep, no spark, and no injector pulse points toward an ECM power/control issue more than a crank sensor problem.
Here's the order I'd check things:
- Verify battery voltage while cranking. It should stay above about 10.5V.
- Check that the ECM has both constant battery power and switched ignition power with the key ON.
- Perform a voltage drop test on the ECM grounds while cranking. Don't rely on an ohmmeter—I've seen corroded grounds pass a continuity test but fail under load.
- Check the main ECM/engine power relay. A bad relay can prevent the ECM from powering the ignition and injectors even though the fuel pump still primes.
- Measure voltage on both sides of every fuse with the key ON. A fuse holder can have enough corrosion to pass a continuity test but not carry current under load.
- Verify the kill switch (lanyard) and ignition switch circuits are working correctly.
- Don't rely only on the crank sensor resistance. A reading of 321 Ω sounds reasonable, but you should also measure its AC output while cranking (typically around 0.3–1.5 VAC).
The biggest clue to me is the
missing warning horn beep. On these engines, you should normally get a horn self-test when you turn the key ON. The fact that the fuel pump primes but there's
no beep, no spark, and no injector pulse makes me suspect the ECM isn't completing its normal startup sequence because it's missing power, ground, ignition feed, or the main relay isn't energizing properly.
Only after confirming all of those items would I hook it up to Mercury CDS/G3 diagnostics or consider an ECM issue.
A couple of questions that would help narrow it down:
- Is this the 115 EFI FourStroke or a 115 Optimax/DFI?
- When you turn the key ON, do the gauges (or SmartCraft, if equipped) initialize, or is the fuel pump prime the only thing that happens?
