Outboard injector reference for the systems we service most: Yamaha F series four strokes from the F115 to the F350, Yamaha HPDI two strokes, and Mercury Optimax DFI including both its fuel and air injectors. Part numbers, system explanations, and why marine injectors foul faster than anything on the road, compiled by the injector cleaning department at Boost Lab, Inc.
Modern outboards split into three injection families, and they fail differently. Yamaha F series four strokes (F115, F150, F200, F250, F300, F350) run conventional port EFI injectors, small Denso style units that behave like automotive injectors and respond the same way to ultrasonic cleaning and flow matching. This is the highest volume marine work on our bench.
Yamaha HPDI two strokes (Z150 through the VZ300) inject fuel directly into the cylinder at pressures far above conventional EFI. That pressure is the whole point of the design, and it is also why HPDI injectors cannot be honestly evaluated on a standard port injection bench. We test them at representative high pressure on our Carbon Zapp equipment, the same capability we use for automotive GDI.
Mercury Optimax DFI is the unusual one: two injectors per cylinder. A fuel injector meters gasoline on the rail side, then an air injector (Mercury calls it the direct injector) uses compressed air from the belt driven compressor to deliver that charge into the combustion chamber as a fine plume. The air rail runs roughly 10 to 15 psi below fuel rail pressure, and the whole system depends on that differential plus even flow across cylinders. A fouled air injector disrupts atomization, a fouled fuel injector leans a cylinder, and on a two stroke, lean is fatal. Both injector types can usually be cleaned and verified; a genuinely faulty air injector cannot be repaired, only replaced, and testing is how you tell the difference.
Boats sit. E10 pump gas absorbs moisture, phase separates in the tank over a layup, and leaves varnish in the fine passages of an injector that might only run 50 hours a year. Add salt air corrosion on connectors and o-rings, and the result is that outboard injectors arrive at our shop in worse condition at lower hours than almost any automotive set. The classic story is an engine that ran perfectly in the fall and misfires on one or two cylinders at the spring launch. That is rarely a coil; it is usually varnish, and a before and after flow report settles it in numbers.
| Application | Years | System | OEM / Ref PN | Notes |
|---|---|---|---|---|
| Yamaha F40 / F50 / F60 | Four stroke | Port EFI | 6C5-13761-00-00 | Denso style top feed |
| Yamaha F115 | 2000-11 | Port EFI | 68V-8A360-00-00 | Set of four |
| Yamaha F115 | 2014-21 | Port EFI | 6DA-13761-01-00 | Later B series |
| Yamaha F150 | 2004-13 | Port EFI | 63P-13761-00-00 | Most common on our bench |
| Yamaha F150 | 2014 and later | Port EFI | 63P-13761-01-00 | Updated version |
| Yamaha F250 / F300 / F350 | 2006-12 | Port EFI | 6AW-13761-00-00 | V6 and V8 offshore |
| Yamaha HPDI two strokes below: high pressure direct injection, tested on our Carbon Zapp bench at representative pressure rather than port injection pressure. | ||||
| Yamaha HPDI Z150 / Z175 / Z200 | 2.6L V6 | HPDI direct injection | 68F-13761-00-00 | High pressure fuel system |
| Yamaha HPDI VZ225 / VZ250 / VZ300 | 2003 and up, 3.3L | HPDI direct injection | 60V-13761-00-00 | High pressure fuel system |
| Mercury Optimax DFI below: two injectors per cylinder. The fuel injector meters gasoline, the air injector (direct injector) delivers the charge with compressed air from the belt driven compressor. | ||||
| Optimax 75-225 HP | 1.5L / 2.5L / 3.0L | DFI fuel injector | 804528 / 37001 | Rail side gasoline metering |
| Optimax 135-150 HP | 2000-06 and later | DFI fuel injector | 804527 / 37003-804841 | Model specific version |
| Optimax all models | 1998-2018 | DFI air injector | 884595A01 family, 8M0065917 | Cleanable, not repairable; Teflon carbon seals |
| MerCruiser sterndrives 4.3 / 5.0 / 5.7 / 6.2 | GM based V6 and V8 | Port EFI | See our GM reference | GM automotive injectors in marine trim |
| Mercury and Verado four strokes | Four stroke | Port EFI | Bench data on request | Conventional service path |
| Suzuki DF and Honda BF series | Four stroke | Port EFI | Bench data on request | Conventional service path |
F150 and F250 sets that ran fine in November and misfire in March. Ultrasonic cleaning, new filter baskets, and o-rings bring the set back with documented flow recovery.
Deposits, moisture, and carbon on the seat disrupt the air plume and can mimic bigger problems, including low compression readings from leaking carbon seals. We clean, test, and verify them; a truly failed unit is identified honestly so you only replace what is actually bad.
HPDI injectors tested at port injection pressure can look fine and still fail on the water. Our Carbon Zapp bench tests at representative high pressure, the same equipment we use for automotive GDI.
Yes, and marine injectors are some of the best candidates for it. Most failures are varnish and deposits from ethanol fuel and storage rather than worn internals. Ultrasonic cleaning with new filter baskets and o-rings, verified by a before and after ASNU flow report, typically restores factory flow at a fraction of OEM replacement cost.
E10 fuel absorbs moisture and leaves varnish in injector passages while the boat sits. The engine that ran perfectly at the end of last season and stumbles at spring launch is the classic storage varnish pattern. Flow testing identifies the affected injectors in numbers before you start replacing parts.
Yes. HPDI is high pressure direct injection, so we test these on our Carbon Zapp bench at representative pressure rather than the port injection pressures most shops use. That is the only honest way to evaluate an HPDI injector, because a unit that passes at low pressure can still misbehave at operating pressure.
Optimax DFI uses a fuel injector to meter gasoline and an air injector to deliver that charge into the cylinder with compressed air from the belt driven compressor. Both need to be healthy: the fuel injector controls mixture and the air injector controls atomization. We clean and test both types; fuel injectors are fully serviceable, and air injectors can be cleaned and verified but not internally repaired.
E-TEC uses a voice coil injector design that is fundamentally different from the solenoid and DFI injectors above, and serviceability varies by model. Reach out through the repair form before shipping E-TEC injectors and we will confirm the right path for your engine.
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