Sylvie Willis
Testing and cleaning fuel injectors is a common concern for boat owners, especially those with saltwater boats, as injectors are prone to corrosion. There are several ways to test fuel injectors, including checking for fuel leaks, testing fuel pump problems with a fuel pressure gauge, and using a multimeter to test fuel injector resistance. Testing fuel injectors can be challenging, as some are located underneath the intake manifold plenum. It is recommended to have injectors serviced and cleaned by professionals to avoid engine damage.
Testing Mercury Fuel Injectors
| Characteristics | Values |
|---|---|
| Fuel Injector Testing Tools | Fuel pressure gauge, Scanner, Multimeter, Noid lights, Test light |
| Fuel Injector Testing Methods | Checking fuel pressure, Testing coils/injectors, Testing injector pulse, Testing injector resistance, Checking for leaks, Checking for debris/residue buildup, Checking for internal short-circuit or open-circuit |
| Fuel Injector Maintenance | Cleaning, Flow testing, Ultrasonic cleaning, Replacing O-rings and filter baskets, Servicing, Reconditioning |
| Common Issues | No fuel through injectors, Engine not starting, Excessive fuel, Hard to start, Black soot, Pressure drop, Voltage issues, Corrosion, Residue buildup, Clogged injectors, Spark issues, Rough idle |
| Suggested Solutions | Grounding wires, Checking voltage, Replacing injectors, Cleaning injectors, Replacing fuel lines, Using premix for lubrication, Sending injectors for testing/servicing |
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What You'll Learn
Testing for internal short-circuiting
- Ensure the key is off and remove the injector wiring harness.
- Connect a test light to the negative terminal on the battery. A test light typically has a finely pointed end and a wire with an alligator clip at the end. Secure a metal-on-metal connection to make the test light work.
- Locate the two wires going into each injector. Each fuel injector will have a metal clip with two wires: one is a 12-volt constant receiving continuous power, and the other should read around 12 volts.
- Check the voltage on all injector wiring harnesses. They should all be around 12 volts. A lower reading indicates excess resistance in the wire, which could be due to an internal short-circuit.
- If you suspect a short-circuit, perform a fuel injector resistance test. This involves checking the internal resistance of the injector's coil winding and comparing it to the factory specification. A multimeter is required for this test.
- If the resistance is not within specification, it confirms an internal short-circuit, and the injector needs replacement.
- Additionally, you can use a mechanic's stethoscope or a long screwdriver to listen for an audible clicking sound from each injector, indicating normal functioning.
It is important to consult a professional mechanic or a certified technician if you are unsure about any of these steps or if you encounter difficulties during the testing process.
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Checking for spark
When testing Mercury fuel injectors, it is important to first identify any potential issues with the spark plugs. A faulty spark plug can cause a misfire in the engine, leading to poor performance or even failure to start.
To check for spark, begin by locating the spark plugs on the engine manifold, positioned on top of the engine. Ensure that the engine is off and cool before proceeding. Wear protective gear, including work gloves and eye protection, to safeguard against any debris or fuel exposure.
Once located, inspect the spark plugs for any visible damage or excessive wear. Clean the spark plug electrodes if they appear blocked with carbon or other residue. Then, proceed to test the spark plugs with a dedicated spark tester. Connect the spark tester to the spark plug wire and observe if a spark is generated. If a spark is present, the spark plug and wire are in working condition.
Additionally, it is recommended to perform a cylinder balance test to identify any 'dead' cylinders. This test helps determine if the issue lies with the spark plug or the fuel injector. If the 'dead' cylinder is not receiving a spark, it is likely the source of the misfire, and further testing of the fuel injectors may not be necessary.
In some cases, you may need to consult a professional mechanic or a specialised repair shop to thoroughly diagnose and resolve any spark-related issues with your Mercury fuel injectors.
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Testing compression
To start the test, safely situate your vehicle. Park on a flat, level surface and apply the parking brake. Open the hood and allow the engine to cool for a short period. You want to perform the test on a slightly warm engine.
Next, locate the main fuse box under the hood. It usually looks like a large, black plastic box and may have writing on top showing the schematic. Remove the fuse box cover by unhooking the clips. Then, locate the fuel pump relay and remove it by pulling it straight up and out of the fuse box. You can identify the proper relay using your repair manual or the schematic on the fuse box cover.
Now, disable the fuel system. If you don't, fuel will continue to be sprayed into the cylinder during the compression test. This can cause lubrication to be washed from the cylinder walls, leading to improper readings and potential engine damage.
Remove the electrical connectors from the ignition coils by pressing on the locking tab and pulling the connector off. Loosen the ignition coils using a ratchet and the appropriate size socket, then remove the small bolts holding them to the valve covers. Take out the ignition coils by pulling them straight out of the valve cover.
Finally, remove the spark plugs using a ratchet with an extension and a spark plug socket. Take out all the spark plugs from the engine. If the spark plugs have not been changed in a long time, you should replace them now.
If the compression test shows that the internal pressure of the cylinder is well below the manufacturer's specifications, there is an internal engine problem.
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Cleaning injectors
There are a few different ways to clean Mercury fuel injectors, ranging from DIY methods to professional services. Here are some detailed instructions for cleaning your injectors:
DIY Methods:
- Using Fuel Additives: One way to clean your injectors is to add a fuel additive to your tank. Sea Foam Marine PRO is a popular choice for Mercury engines, and it can be used by adding a full can to a low tank of fuel (around 1/4 tank). Then, operate the engine for at least 20 minutes before refuelling. This method is inexpensive and effective, but it may not be suitable for all engines.
- Adding Oil to the Fuel: Some Mercury owners suggest adding a little oil to the fuel as a simple way to lubricate and protect the injectors. This can be done by running a 100:1 premix in addition to the oil injection system. However, this method may not be suitable for all engines, and it is important to use the correct oil and fuel mixture.
- Using Quickleen: Quickleen is a product that can be added to a test tank and run through the engine to clean the injectors. This method can be effective, but it may not be as accessible or affordable as other options.
Professional Services:
- Sending to a Reputable Shop: It is generally recommended to send your injectors to a reputable shop for professional cleaning. Shops like BrucatoFIS Inc. and Brucato offer testing, cleaning, and replacement services for fuel and air injectors. They have the necessary equipment and expertise to properly clean and calibrate the injectors.
- Using a Scanner: If you have access to a scanner, you can check for codes and test your coils and injectors. This can help you identify any issues and determine if professional cleaning or servicing is needed.
Preventative Measures:
- Use a Fuel Stabilizer: The best way to keep fuel injectors clean is to use a stabilizer every time, while the injectors are still on the engine. This helps prevent fuel buildup and keeps the injectors functioning optimally.
- Avoid Ethanol Blends: Ethanol blends can be corrosive to hoses, filters, O-rings, and fuel pumps, and the debris from these components can end up in the injectors. Using "straight gas" or non-ethanol blends can help prevent this issue.
- Double or Triple the Dosage Before Storage: If you plan to store your boat for longer than a month, it is recommended to double or triple the dosage of fuel additives to prevent fuel injector problems.
Please note that fuel injectors can be difficult to access and clean properly without the right tools and expertise. If you are unsure about any of these methods or if your engine is experiencing significant issues, it is always best to consult a professional or your boatyard service manager for guidance.
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Testing for leaks
One of the easiest ways to detect a fuel injector leak is through a visual inspection. Pop the hood and inspect each fuel injector, paying attention to any wet spots or residual gasoline smell. A shiny substance that resembles gasoline indicates a potential leak. Sometimes, instead of an apparent wet spot, you may notice a dirtier injector due to fuel acting as a magnet for dust and debris.
You can also use a mechanics stethoscope to listen to each injector fire off with the engine running. If one is not "clicking", it is likely stuck open and leaking fuel. Alternatively, you can start the engine and let it idle for a short time before stopping the engine. Then, pull the line off the pressure regulator and shake it. If fuel comes out, this indicates a leak.
Another method is to turn the key to "ON", let the pump prime the fuel rail, then turn the key "OFF" and pinch the return line while watching the fuel pressure gauge. If the pressure starts to drop rapidly, your injectors are likely leaking.
It is important to note that fuel injector leak testing should ideally be done under operating pressure. However, most DIY methods do not have the proper diagnostic equipment to test leaking injectors accurately. Therefore, sending your leaking fuel injector to a professional service for testing and cleaning is recommended.
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Frequently asked questions
If you're experiencing issues with your Mercury engine, it's important to diagnose the problem correctly before jumping to conclusions. Start by consulting the OEM manual and following the troubleshooting instructions for your specific engine. Check the fuel pressure regulator and the injector pulse with a noid light. If you suspect leaky injectors, unbolt the fuel rail, pressurize it, and then check for leaks.
There are several indicators that your Mercury fuel injectors might not be functioning properly. For example, you may notice that your engine has become harder to start, or you may observe black soot on the transom after a day of boating. Additionally, a rapid pressure drop when the engine is shut off could be a sign of faulty injectors.
There are a few methods you can try to test Mercury fuel injectors. One approach is to start the engine, let it idle for a short time, then stop the engine and check the pressure regulator for leaks. Another method involves taking the injector lead off and jumping the injector with a 12-volt radio battery after the fuel pump is turned on. If the injector opens, the issue is likely with the voltage source rather than the injector itself.
Regular cleaning and servicing of Mercury fuel injectors are crucial, especially in saltwater environments where corrosion is a concern. Consider using a product like Sea Foam Marine PRO, which can be added to your fuel tank and then run for at least 20 minutes to effectively clean the injectors. Additionally, some recommend running a 100:1 premix to provide lubrication and protect the injectors from corrosion.
