Fuel Injector Cleaning

Article & Photos By John Tiger Jr.

Fuel injectors are a vital element in the lifecycle of your engine. Periodic maintenance is just what the doctor ordered.

Having engine problems? Yours won't start with a quick key flick, idles roughly, and surges through midrange and full throttle? It's likely the fuel injectors are dirty.

Dirty injectors make the fuel spray pattern intermittent and splotchy instead of the fine mist it needs to be. How to solve it? While it's possible to rig a simple home-cleaning method, the best remedy for dirty injectors is to remove and send them to a professional.

Marine fuel injectors live a much tougher life than their automobile counterparts. Inboard, sterndrive, and four- and two-stroke outboard motors are all subject to fuel and injector problems. The challenge is the same: keeping fresh fuel in the tanks, having annual fuel-system maintenance, and frequently using the boat. Today's ethanol-blended fuel, if not treated properly or if not used within a reasonable amount of time, can create fuel-system degradation — bad for any type of engine.

Hoses, filters, O-rings, and fuel pumps suffer from the corrosive effects of the alcohol in fuel, often disintegrating from the inside out, emitting debris that ends up in the injectors. Proper engine winterization and fuel treatment are critical, with northern boating enthusiasts facing the greatest challenge. If winterization isn't performed and fuel isn't stabilized with the proper treatment to prevent evaporation and varnishing, expensive fuel-injector cleaning and calibrating are often the remedy. Eventually the injectors can fail and/or not provide enough fuel to ensure the engine gets enough, and the engine can be damaged internally.

What The Pros Say

We discussed injector maintenance and cleaning with Brucato Fuel Injector Service Inc. owner Rich Szczerbala. Szczerbala recommends fuel-system service once a year or every 100 hours of use. This includes all fuel filters (check to make sure you know where all of yours are located) and any degraded fuel line replacement. Professional fuel-injector service (cleaning, calibration, repair) should be done every 300 engine hours or every three to four years.

What You Can Do

On most outboards, and even some inboards, just accessing the injectors to remove them is a pretty involved process. They're often embedded deep in the intake manifold behind the air silencer and the throttle bodies, making them complicated to remove. Our advice: If you're not already reasonably skilled as a mechanic, take your rig to the dealer. Remember, you'll have to put everything back together as it was and have it run right when you're done.

If you're intent on DIYing it, you can do a reasonable, quick-fix job cleaning dirty injectors after you've removed them from the engine by simply connecting the fuel input end to a hose that's submerged in carburetor cleaner or a similar solution (even Simple Green works well). Raise the solution container above the level of the injector (so it can gravity feed) and aim the pintle (output) end into a clear jar. Lastly, connect the positive and negative terminals on each injector to a 12-volt battery (the one from your boat will do fine) with jumper wires. When connected to the battery, the injector will "fire," spraying the cleaning solution into the jar, and you can see the spray pattern. Pulsing the voltage on and off by alternately connecting and disconnecting the positive jumper will clear the injectors in a few minutes.

Injector numberingMark injectors with their locations so you can reinstall in the correct slot.

Remember, this fix may get you back on the water, but is by no means the best way to thoroughly and properly clean injectors. At best, you'll be able to clear up the sputtering idle, help starting problems, and get out on the water again. At worst, you may cause engine damage if you run the engine at full throttle and/or under heavy load and the injectors are still partially clogged, because the engine won't be receiving enough fuel. As noted, for best results have the injectors removed, cleaned, and reinstalled professionally.

Brucato injector cleaningProfessional fuel-injector service includes cleaning, calibration, and repair.

High Risk!

The consequences of neglecting this vital service can be extremely expensive. First, you risk major engine damage due to lean mixture conditions as a direct result of the clogging in one or more injectors. Just like with a dirty carburetor, the air/fuel mixture that gets to the piston and cylinder has less fuel than it needs because the clogged injector can't spray the properly metered amount of fuel. The cylinder and piston use the fuel as "food," but the fuel mix also acts as a coolant. Without that coolant, the piston expands with heat and eventually "sticks" inside the cylinder, often causing major internal engine damage. This is especially critical and a major cause of engine failure in two-stroke engines, which fire every stroke.

In addition, the injectors themselves may be ruined as a result of the fuel varnish gelling and drying/hardening inside the injector. New injectors for Mercury engines, for example, range in price from $160 to more than $600 each! For a V-6 engine with six injectors, this could add tremendously to an already high repair bill.

Prevent The Problem

Gas Shok 8-oz-bottle

The best way to keep fuel injectors clean is to do so while they're still on the engine. Using a fuel additive like Sta-Bil, StarTron, or Gas-Shok Plus (pictured) on a regular basis will help you avoid the problem altogether by preventing condensation buildup and resulting deterioration from rust and alcohol degradation in your boat's fuel system. Treating the fuel as you use it during the season is great practice, but doubling or tripling the dosage (after checking with the manufacturer for recommendations and warranty information) before off-season layup is very cheap insurance against fuel-injector problems in the spring. At less than $20 for an 8-ounce bottle that will treat up to 80 gallons, what do you have to lose? 

John Tiger Jr. is an outboard master technician who builds racing engines. He got his first outboard at age 7, and has owned more than 60 boats and outboards since.

— Published: December 2017


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