The Essential Guide to Your 1999 Evinrude 9.9 4 Stroke Fuel Pump: Maintenance, Troubleshooting, and Replacement

A faulty or failing fuel pump is one of the most common causes of running problems on a 1999 Evinrude 9.9 4 Stroke fuel pump. Understanding its function, recognizing failure symptoms, knowing how to test it, and being able to replace it are crucial skills for any owner of this reliable but aging outboard. This comprehensive guide covers everything you need to know to keep your engine's fuel delivery system operating perfectly.

What the Fuel Pump Does & Why It Matters on Your 1999 Evinrude 9.9

The fuel pump on your 1999 Evinrude 9.9 4 Stroke has one critical job: draw fuel from the tank and deliver it at the correct pressure to the carburetor(s). Unlike larger high-pressure fuel injection systems, this engine uses a relatively simple mechanical diaphragm pump powered by crankcase pressure pulses. Here's how it works within the system:

1. Fuel Intake: Fuel is drawn from the tank through the primer bulb and fuel line.
2. Pump Operation: Engine crankcase pressure changes act upon a diaphragm inside the pump. These pressure pulses cause the diaphragm to flex up and down.
3. Check Valves: The pump has small internal one-way valves. The diaphragm movement, combined with these valves, creates suction to pull fuel in on the intake stroke and pushes it out towards the carburetor on the discharge stroke.
4. Carburetor Delivery: Fuel is pumped into the float bowl(s) of the carburetor. The float and needle valve assembly inside the carburetor regulate the fuel level within the bowl. As the engine consumes fuel, the float drops, allowing the needle valve to open and replenish fuel from the pump.
5. Excess Fuel: Any fuel exceeding the carburetor's immediate needs is typically routed back to the tank via a return line, helping to cool the pump and prevent vapor lock.

Failure of the fuel pump on your 1999 Evinrude 9.9 4 Stroke directly interrupts this vital flow. Without adequate fuel pressure and volume, the carburetor float bowl cannot fill correctly, leading to immediate engine performance issues that worsen over time.

Spotting Trouble: Symptoms of a Failing '99 Evinrude 9.9 Fuel Pump

Recognizing the signs early can save you from being stranded. Symptoms often start intermittently and worsen progressively:

1. Difficulty Starting & Stalling: The most common initial sign. The engine cranks but won't start, or starts briefly then dies – especially when cold. This happens because the pump isn't delivering enough fuel initially to fill the float bowl(s).
2. Loss of Power & Surging: While running, particularly under load (accelerating, pushing against current, or carrying weight), the engine suddenly loses power, bucks, surges, or stalls outright. This indicates the pump can't keep up with the engine's fuel demand.
3. Only Runs with Primer Bulb Squeezed: Manually squeezing the primer bulb provides temporary fuel pressure, forcing fuel past the weak pump. If the engine runs normally only while you squeeze the bulb or shortly after, the pump is almost certainly failing.
4. Engine Dies at Idle or Low RPM: An overly weak pump might not supply adequate fuel to maintain idle speed consistently, causing the engine to die when throttling down.
5. Lack of Prime: Normally, squeezing the primer bulb until firm primes the fuel system. A leaking diaphragm inside a failed pump often prevents the bulb from getting firm, or it goes soft again very quickly.
6. Fuel Leaks: While less common than failure modes related to low output, visible fuel leaking from the pump body or the seams of its diaphragm cover is a definitive sign the diaphragm is ruptured and the pump needs immediate replacement.
7. "Vapor Lock" Type Symptoms (Especially Hot Weather): A weak pump struggles more when fuel vapors form in hot conditions, potentially mimicking vapor lock symptoms – hard restarting when warm, hesitation, stalling.

Diagnosing Your Suspect Fuel Pump

Before condemning the pump, perform these checks:

1. Check the Basics FIRST:

   • Fuel Supply: Is there fresh, clean fuel in the tank? Old or contaminated fuel causes identical symptoms.
   • Tank Vent: Is the fuel tank vent open? A clogged vent creates a vacuum in the tank.
   • Fuel Lines & Bulb: Inspect all lines for kinks, cracks, or leaks. Squeeze the primer bulb: it should get firm easily without collapsing and stay firm. A faulty bulb or leaky lines compromise the entire system.
   • Fuel Filter: Check the inline fuel filter (usually clear plastic). Is it clogged with debris or water? Replace it regardless if it's old.
   • Quick Connects: Ensure the fuel line quick-connect fitting on the engine is fully seated and not damaged.
   • Carburetor Issues: While the pump might be a common failure point, significant carburetor problems (like stuck floats, blocked jets) can mimic pump failure. Rule out gross carb issues if possible.

2. The "Clear Tubing" Pressure Test (Simplest Method):

   • Obtain a few feet of clear plastic fuel tubing (small diameter fuel line).
   • Disconnect the fuel supply line from the inlet side of the fuel pump.
   • Connect one end of the clear tubing to the pump's inlet nipple. Place the other end in a container of fresh fuel.
   • Disconnect the fuel outlet line from the fuel pump to the carburetor. Connect a length of clear tubing to the pump's outlet nipple and route it into a clean container.
   • Prime the system by squeezing the primer bulb a few times (connect temporary line from bulb to pump inlet if needed).
   • Start the engine. Observe the fuel flow in the outlet clear tubing. You should see strong, steady pulses of fuel exiting the pump. If flow is weak, sputtering, non-existent, or primarily bubbles, the pump is suspect. Caution: Work in well-ventilated area; manage fuel safely.

3. Vacuum & Pressure Gauge Test (More Advanced & Definitive):

   • Vacuum Test (Pump Inlet): A vacuum gauge (0-15 inHg) connected between the fuel tank outlet (after the primer bulb) and the fuel pump inlet measures the pump's suction ability. Excessive vacuum (over 4-6 inHg at idle, higher at WOT) indicates inlet restriction (kinked line, clogged filter, tank vent) OR a pump struggling to pull fuel. Test without restriction first.
   • Pressure Test (Pump Outlet): Connect a low-pressure liquid-filled fuel pressure gauge (0-15 PSI range) to the outlet of the pump (before the carburetor). Refer to your specific service manual for exact pressure specs, but typical pressures for these engines range from 2 PSI to 6 PSI under normal operation. Pressure should be reasonably steady, increasing slightly with engine speed (RPM). Pressure significantly below spec or fluctuating wildly confirms pump failure.
   • Return Flow Check: Disconnect the fuel return line at the tank and direct it into a container. Measure the flow volume at idle. While specs vary, a robust return flow is expected. A trickle or nothing suggests pump output problems or a blockage in the return system.

Replacing the Fuel Pump on Your 1999 Evinrude 9.9 4 Stroke

Once diagnosis confirms the need, replacement is generally straightforward. Critical elements: using the correct replacement part and safely managing fuel.

Procuring the Correct Replacement Fuel Pump:

• OEM Part: The original pump part number for a 1999 Evinrude 9.9 4 Stroke (E10REL4S, E10RL4S, E10RC4S) is Omc/Brp Part # 5006820. While this specific pump (often branded Johnson/Evinrude or Sierra aftermarket) might be available, compatibility cross-references are crucial.
• Aftermarket Options: High-quality aftermarket pumps from reputable brands like Sierra International (Often # 18-7352 or variations – VERIFY COMPATIBILITY) or CDI Electronics are excellent and usually more affordable alternatives. ALWAYS confirm the aftermarket pump specifically lists compatibility with the 1999 Evinrude 9.9 4 Stroke (9.9hp) model. Don't rely solely on generic "fits 9.9hp" claims.
• Universal Pumps: Universal pulse pumps exist. Mounting, flow rate, and inlet/outlet port size MUST match the engine's requirements. Exercise caution unless you are experienced. OEM or direct-fit aftermarket is preferable for reliability.
• The "1998-2005 Honda BF10/BF8" Connection: Crucially, the 1999 Evinrude 9.9 4 Stroke fuel pump is identical to those used on the Honda BF8A/BF10A outboards (approximately 1998-2005). Pumps listed for those Honda models will fit your Evinrude perfectly and are often easier to find. Verify the outlet port configuration matches yours (straight barb or angled). This cross-compatibility is a huge benefit for owners.

Replacement Procedure:

• Safety First: Work in a well-ventilated area away from sparks/open flame. Have a fire extinguisher handy. Relieve fuel system pressure by squeezing the primer bulb until resistance is gone (carefully). Place absorbent pads under the work area. Disconnect the battery negative terminal.
• Access: Locate the fuel pump. It's typically mounted directly to the side of the engine block, driven by crankcase pressure via a small hose connected to a nipple on the block. On some Evinrude models, it might be bracket-mounted nearby.
• Disconnect Fuel Lines: Carefully note the routing and connections of: The fuel supply line (coming from primer bulb/tank), the fuel outlet line (going to the carburetor), and the fuel return line (if equipped, going back to tank). Use appropriate pliers designed for fuel line clips. Plug or cap the fuel lines and block nipple immediately to minimize fuel spillage and air ingestion. Capture residual fuel.
• Remove Mounting Bolts/Screws: Remove the bolts or screws securing the pump to its mounting point (block or bracket).
• Install New Pump: Transfer any necessary gaskets or spacers (take photos first!) to the new pump. Carefully align the new pump to the mounting surface. Reinstall the mounting bolts/screws and tighten them securely but do not overtighten, especially if mounting to the block.
• Reconnect Fuel Lines: Connect the fuel supply, outlet, and return lines to the correct ports on the new pump. Ensure all connections are secure and double-clipped if necessary. Pay attention to the pulse hose connection (to the block nipple) – ensure this is tight and the hose is in good condition (replace it if cracked or hardened).
• Prime the System: Reconnect the battery. Squeeze the primer bulb slowly and firmly until it becomes hard and stays hard. This fills the new pump and carburetor float bowls.
• Leak Check: Before starting, inspect ALL fuel line connections for ANY sign of leakage. Carefully sniff for fuel odors. Fix any leaks immediately.
• Start & Test: Start the engine. It may take a little longer to start as the new pump builds pressure and fuel fills the system fully. Once running, check for smooth idle and responsiveness to throttle. Monitor carefully for leaks again under pressure. Take the boat for a water test under load to confirm the problem is resolved.

Keeping Your Fuel Pump Healthy: Preventative Maintenance

Extend the life of your new pump and the entire fuel system:

1. Use Clean, Fresh Fuel: Stale fuel gums up components. Use ethanol-free fuel (if available in your area) or treat every tank of ethanol-blended fuel with a marine-specific stabilizer like Sta-Bil Marine Ethanol Treatment or Sea Foam Motor Treatment.
2. Change the Water Separating Fuel Filter Regularly: This is the BEST defense for your fuel pump and carburetors. Follow the manufacturer's interval (often annually or every 100 hours) or change it immediately if you suspect water or debris in the system.
3. Replace Inline Filters: If you have a small inline filter, replace it annually or when it looks dirty.
4. Inspect Fuel Lines Annually: Look for cracks, stiffness, chafing, or leaks. Replace lines every 5-7 years or sooner if damage is found. Use USCG-approved marine fuel line (A1-15).
5. Maintain the Primer Bulb: Ensure it primes hard and stays firm. Replace it if soft, leaking, or not priming well. Check its inlet screen if equipped.
6. Winterize Properly: If storing the engine for an extended period, run fuel stabilizer through the entire system (see point 1) according to the stabilizer instructions before shutdown. Fogging the cylinders is separate.
7. Avoid Running the Engine Out of Fuel: This can momentarily cause the pump to run dry and create internal heat/wear.

Addressing Common Owner Concerns

• Can I rebuild the old pump?: Genuine rebuild kits (#5006820KIT) were sometimes available. However, given the age and criticality of the part, most mechanics and knowledgeable owners recommend installing a complete new pump for reliable service. Rebuilding a complex diaphragm with integrated valves requires precision.
• Is there an upgrade?: The original pulse-driven pump design is simple and effective for this carbureted engine. There is no practical or necessary "upgrade" to a different type of pump for standard operation. Installing the correct new OEM or high-quality aftermarket pump is the upgrade over a worn-out one.
• My engine only has one carburetor?: The 1999 Evinrude 9.9 4 Stroke has a single carburetor model (E10REL4S). The fuel pump feeds it directly. Procedures are the same as for twin-carb models; there's just only one outlet line.
• My engine runs hot/cold rough? Could it be the pump?: While primarily a fuel delivery device, severe pump failure impacting mixture can indirectly contribute to cooling issues under load. Always check the obvious cooling system components first (tell-tale stream, impeller, thermostat). Pump failure is more directly linked to power loss/surging.
• Can fuel pump issues mimic ignition problems?: Absolutely. Both ignition failure (spark loss) and fuel starvation cause stalling and refusal to start. Performing basic fuel delivery checks (like the primer bulb trick) helps differentiate. Use the diagnostic tests outlined earlier.

Conclusion: Ensuring Reliable Fuel Delivery for Years to Come

The 1999 Evinrude 9.9 4 Stroke fuel pump is a critical but manageable component. Recognizing the symptoms of failure (hard starting, stalling, loss of power especially under load, reliance on the primer bulb) is the first step. Simple diagnostics like observing fuel flow or testing with a pressure gauge can confirm your suspicions. Replacement, while requiring care with fuel lines and safety, is a straightforward task, especially since the part is cross-compatible with Honda BF8A/BF10A pumps, ensuring good availability.

Investing in a quality replacement pump – be it genuine Evinrude/BRP, Sierra, or CDI – and committing to preventative maintenance with fresh, clean fuel, regular filter changes, and line inspections will guarantee that your trusty 1999 Evinrude 9.9 continues to deliver reliable performance on the water for many seasons ahead. Don’t let a small $50-$100 pump be the reason you miss out on a great day of boating. Keep that fuel flowing reliably!