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Mercury Mariner outboards 135 150 optimax DFI Troubleshooting Guide

Symptom 1. Engine cranks but won’t start

Cause: 1.0 Lanyard stop switch in wrong position. Action Reset lanyard stop switch

Cause: 1.1 Reset lanyard stop switch. Action Replace/charge battery. Inspect condition of starter motor. Check condition of battery terminals and cables.

Cause:1.2 Low air pressure in rail (less than 70 psi at cranking) . ActionInspect air system for leaks. Inspect air filter for plugging (air pressure measured on port rail). Inspect air compressor reed valves if necessary

Cause:1.3 No fuel. ActionCheck that primer bulb is firm. Key-on engine to verify that fuel pump runs for 2 seconds and then turn off. Measure fuel pressure (valve on starboard rail). Fuel pressure should be 10 ± 1 psi greater than the air pressure.

Cause:1.4 Low fuel pressure.ActionCheck fuel pressure from low pressure electric fuel pump (6–10 psi). Check for fuel leaks. If fuel pressure leaks down faster than air pressure, seals on fuel pump may be leaking.

Cause:1.5 Sheared Flywheel Key.ActionRemove flywheel and inspect key.

Cause:1.6 Blown fuse Replace fuse. Action Inspect engine harness and electrical components.

Cause:1.7 Main Power Relay not functioning. Action Listen for relay to “click” when the key switch is turned on.

Cause:1.8 Spark Plugs. Action Remove fuel pump fuse. Unplug all direct injector connectors. Remove spark plugs from each cylinder. Connect spark plug leads to Spark Gap Tester 91-830230T. Crank engine or use DDT output load test for each ignition coil and observe spark. If no spark is present, replace appropriate ignition coil. If spark is present, replace spark plugs.

Cause:1.9 ECM not functioning. Action Injection System: Listen for injector “ticking” when cranking or connect spare injector to each respective harness. Ticking should start after 2 cranking revolutions.
Ignition System:
– Check for proper operation by using Inductive Timing Light 91-99379.
– Check battery voltage (RED/YEL Lead) @ ignition coils.
– Check for blown fuse (C15).
– Check battery voltage to fuse from main power relay (PURPLE Lead).
– Check for shorted stop wire (BLK/YEL).
– Check crank position sensor setting [0.015 in. – 0.040 in. (0.38mm – 1.01mm)] from flywheel or for defective crank position sensor.
– Defective ECM.
Power Supply:
Clean and inspect remote control
male and female harness connectors.

Symptom 2. Engine cranks, starts and stalls
Cause:2.0 Abnormally high friction in engine . Action Check for scuffed piston or other sources of high friction.

Cause:2.1 TPS malfunction. Action Check motion of throttle arm. Stop nuts should contact block at idle and WOT. Check TPS set-up. Must connect DDT with adapter harness (84-822560A5) to ECM.

Cause:2.1 Remote control to engine harness connection is poor. Action Clean and inspect male and female connectors.

Symptom 3. Engine idle is rough
Cause:3.0 Fouled spark plug. ActionFouled spark plug –If carbon bridges electrode gap or if it is completely black. –If it is not firing and is wet with fuel.

Cause:3.1 Failed direct injector. Action Failed direct injector.

Cause:3.2 Failed fuel injector. Action Refer to specifications for ohm test.

Cause:3.3 Flywheel key sheared. ActionRemove flywheel and inspect key

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