Mercury Optimax losing power: air compressor and fuel pressure
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Applies to: Mercury Optimax 115 to 175 hp
Symptoms
- Loss of top-end power
- Warning horn and guardian mode
- Rough running, hard starting
Why it happens
The Optimax uses compressed air to inject fuel. A worn air compressor or a fuel/air pressure regulator out of spec upsets the fuel-air balance and the engine protects itself.
How to fix it
- Read the fault codes with diagnostic software.
- Check fuel pressure and air pressure at the rail against the manual spec.
- Check the compressor intake and hoses for leaks.
- Rebuild or replace the compressor if air pressure is low.
Tools and parts
- Fuel and air pressure gauges
- Compressor rebuild kit
What the factory service manual covers
Direct fuel injection: air and fuel pressure specs, compressor service, diagnostics. The full procedure, specs and wiring diagrams are in the factory service manual for your machine.