EFI Outboard Cranks but Won't Start, No Key-On Beep or Fuel Pump Hum

Make sure the shift lever is in neutral. Turn the key to ON (not START), then stop and wait three to five seconds, listening at the engine with the cowl off if you can. Many owners crank right away and never notice whether the pump primed.

• Beep and pump hum now present: the computer is waking up. Your no-start is a fuel or spark problem: see the fuel pump and no-spark guides.
• Beep but no pump hum: the computer is awake; look at the fuel pump fuse, the fuel pump relay and the pump circuit (step 7 and the fuel pump guide).
• Nothing at all: keep going.

On many engines the computer won't wake up, or won't allow the engine to run, unless the kill-switch circuit is closed. The Coast Guard describes the cut-off link as either a coiled lanyard or an electronic fob; once the link is reinstalled, the engine can be restarted.

• Make sure the clip is fully seated. Try your spare lanyard clip if you have one.
• Wiggle the switch while a helper turns the key on. A switch that's corroded inside can stay "open" even with the clip in place, and owners in forums often find this after hours of chasing other parts.
• With a wireless system, check the fob battery and that the fob is paired and within range.

Depending on the setup, BoatUS notes the engine may not even crank with the kill switch out; on others it cranks normally but never starts, which is exactly this symptom.

Put the multimeter on the battery posts (not the cable clamps).

• At rest: BoatUS suggests a minimum of 12 volts for starting. Lower than that, charge the battery and try again.
• While cranking: have a helper crank for a few seconds while you watch the meter. A battery can have enough left to spin the starter but sag so low during cranking that the computer drops out or resets, and the engine never fires. Your service manual or dealer can tell you the minimum cranking voltage for your engine.

If voltage drops hard, have the battery load-tested; Yamaha notes any auto parts store can do this. Then recheck the connections in step 4. A deep-cycle battery that's run flat by the stereo or fish finder is a common culprit.

Turn the battery switch off before you touch the cables. Yamaha recommends removing each terminal connection and cleaning both sides down to bare, shiny metal, then reinstalling it tight with hex nuts and lock washers, not wing nuts. A connection can look clean on the outside and still be corroded where the metal touches. Mercury's battery inspection quick tip adds two habits: use a correctly sized wrench rather than an adjustable one so it can't slip, and take the negative cable off before putting a wrench on the positive terminal, then refit the positive's rubber boot before reconnecting the negative. That keeps a slipping wrench from shorting the battery.

Check both cable ends: at the battery, at the battery switch, and where the cables bolt to the engine (the starter solenoid or a terminal block on the engine, and the engine ground).

Most outboards have a main fuse or fuses in a holder on the engine harness, often near where the battery cables come into the engine, plus several smaller fuses for the computer, fuel pump and accessories. BoatUS describes the typical main fuse as being in a red holder on the harness. Your manual shows yours.

• Pull each fuse and look at it in good light. A blown blade fuse has a broken or melted metal strip.
• Replace a blown fuse only with one of the same rating.
• Mercury's advice after an electrical fault is the right rule for all brands: replace the fuse and test, and if it blows again, get the dealer involved. A fuse that blows again means a short somewhere, and a bigger fuse only moves the damage to the wiring.

Many EFI outboards power the computer, injectors and fuel pump through a main relay (sometimes called the main power relay or ECM relay), and the computer then switches the fuel pump relay. Have a helper turn the key to ON while you hold a finger on the relay or listen closely.

• A click: the relay is getting its signal. That doesn't prove its contacts are good, but it points away from the key switch and kill circuit.
• No click: the relay isn't being told to close (look upstream: lanyard circuit, key switch, a fuse, the harness plug), or the relay itself has failed.

If your engine uses two or more relays with the same part number (your manual or the printing on the relay shows it), you can swap a suspect relay with one that you know works and try again. If the problem moves, you've found it.

Look into the relay socket while it's out: green or white crust, a burned or melted spot, or a loose pin are common. Clean with contact cleaner, let it dry and reseat firmly. Never swap in a relay that merely "looks the same"; the internal wiring can differ.

BoatUS lists the main power plug between the engine wiring and the boat as a standard no-start check. On outboards it's usually a large round or rectangular plug under the cowl or near the rigging tube.

• With the battery switch off, unplug it, photograph it and look for corrosion, water, pins pushed back into the plug, or a broken latch.
• Clean, apply a light film of dielectric grease if your manual allows, and reconnect until it locks.
• Follow the harness to the helm. Behind the dash, look for loose or corroded connections on the back of the key switch and the kill switch, and for any accessory someone tapped into the engine harness.

A bad ground can kill the computer's power just as well as a bad positive wire. Find the main ground (negative) cable from the battery to the engine and any ground strap or wire bolted to the powerhead. Remove, clean to bare metal, reinstall tight and spray with a corrosion protectant. Yamaha also suggests wiggling wires and connectors to find loose ones, and checking under the dash and in the bilge where wires meet.

A no-beep, no-start that appears right after something else happened usually has a simple link:

• The battery was replaced or reinstalled backwards. Mercury says to check the fuse or fuseable link first, and then have a dealer inspect the boat, because a reversed battery can damage the voltage regulator, rectifier, gauges, the computer and wiring.
• New electronics or a new battery switch wired into the engine harness or key switch.
• Winter storage: rodents chewing harness wires (see the rodent prevention guide).
• You just refueled. On a boat with a built-in tank, BoatUS warns that a leaking fill hose can flood the bilge with so much gasoline vapor that the engine won't run, and that the danger comes when fresh air thins those fumes and a spark ignites them. If it refuses to start right after fueling, stop cranking, don't open hatches or flip switches, get everyone off and check for a spill (call 911 if you find one).
• A dunking or heavy spray into the cowl, or the engine was submerged (see the submerged engine guide and get it to a dealer quickly).

When the beep and pump hum come back, try to start it normally. If it still won't start, the computer is awake and the problem has moved to fuel or spark: water in the fuel filter, an empty or stale tank, a clogged vapor separator, a fuel pump that runs but doesn't build pressure, or an ignition fault. The fuel pump, EFI vapor separator and no-spark guides take it from there.

If you have good battery voltage while cranking, good fuses and grounds, a closed lanyard circuit and still no beep or prime, it's time for a dealer with the factory diagnostic tool. They can read stored fault codes and check the computer, key switch circuit and harness properly.

Tell them exactly what you found: voltage at rest and while cranking, which fuses and relays you checked, whether the relay clicks, and what changed recently. It saves diagnostic time, and diagnostic time is what you pay for.