Regan Brown
The Detroit Diesel 671 engine is a unit injector type engine, meaning all fuel pressure required for atomization occurs inside the injector. If your Detroit 671 engine won't start despite replacing the fuel pump, there are several troubleshooting steps you can take. First, check for air leaks in the fuel lines, which can prevent proper fuel delivery. Next, bleed the fuel system of any air using the bleed screws on the fuel filter and injectors. Then, inspect the injectors to ensure they are functioning properly, and clean or test them if necessary. Additionally, check the glow plugs, electrical connections, and the starter. If these steps do not resolve the issue, further diagnostics or consultation with a technician specializing in Detroit engines may be required. It is important to prioritize safety when working on engine maintenance, especially with antique engines, to avoid potential injuries from engine parts.
| Characteristics | Values |
|---|---|
| Fuel Pressure | 60psi when the engine is running |
| Troubleshooting Steps | Check for air leaks, bleed the fuel system, inspect injectors, check glow plugs, verify electrical connections, examine the starter, perform a compression check, check timing |
| Disassembly Steps | Drain the engine oil, gather tools and equipment, set up work area, unbolt the oil pan, remove the oil pan |
| Distributor | DieselPro |
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What You'll Learn
Identify the pump type
The first step in identifying the fuel pump type for a Detroit Diesel 6-71 engine is to determine whether you have a right-hand or left-hand pump. This can be done by visually inspecting the pump and comparing it to images of known right-hand and left-hand pumps for reference.
Diesel Pro, a distributor of parts for Detroit Diesel 6-71 engines, provides pictures for comparison to help identify the correct pump type. They also offer a troubleshooting guide to assist in the identification process.
Additionally, when identifying the pump type, it is essential to consider the specific characteristics of your engine. For example, is it a non-turbo engine with a 4-valve head type? This information will help ensure that you select the appropriate fuel pump for your specific Detroit Diesel 6-71 engine configuration.
By following these steps and cross-referencing visual cues with available resources, you should be able to successfully identify the fuel pump type for your Detroit Diesel 6-71 engine.
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Check for air leaks
If your Detroit Diesel 671 engine won't start despite replacing the fuel pump, filter, and lines, and you have confirmed fuel pressure, you should check for air leaks.
Air leaks in the fuel lines can prevent proper fuel delivery, so it is important to ensure there are none. To check for air leaks, you should look for any signs of fuel leaks, as air entering the fuel system through leaks can cause hard starts. Symptoms of fuel leaks include diesel fuel pooling under the engine, drips on engine components, or fuel-soaked hoses. If there are no visible signs of fuel leaks, you can try circulating some fuel to confirm flow. If the fuel tank is below the level of the fuel pump, there may be an issue with the air bleeding process.
If there are no weep hole leaks from the pump, this is a good sign. However, you should also ensure that you have the correct restrictor fitting on the outside of the head on the return line installed, as this could also cause issues. A brass square body fuel restrictor is needed on the outlet of the cylinder head, before the fuel line goes back to the fuel tank. Without this in place, the system cannot build fuel pressure.
If you have checked for air leaks and addressed any issues, you can move on to the next troubleshooting steps, which include bleeding the fuel system, inspecting injectors, checking glow plugs, verifying electrical connections, and examining the starter.
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Bleed the fuel system
Bleeding the fuel system of a Detroit Diesel 671 engine is a critical skill for anyone intending to be on the water for an extended period. Before attempting to bleed the fuel system, it is important to determine how air entered the system to prevent re-entry. Diesel engines should never run dry as this will cause an airlock.
To bleed the fuel system, first locate the fuel filter and determine whether it has a built-in bleeder screw. If it does, position a clean rag or towel beneath the bleeder screw to catch any fuel spills. Then, use a wrench or bleeder screw key to loosen the screw slowly in a counter-clockwise direction. A mixture of air and fuel will begin to bleed from the screw. Allow this to continue until only fuel (without air bubbles) flows from the screw. Finally, tighten the bleeder screw securely.
If the fuel filter does not have a bleeder screw, you may need to loosen the filter slightly to allow the air to escape. If your fuel filter does not have a bleeder screw, or if you suspect that air remains in the system, you may need to bleed the fuel system at the fuel injectors.
After bleeding the fuel system, attempt to start the engine. If the engine starts, allow it to idle for a few minutes while monitoring for any signs of rough idle or reduced power. As the engine idles, inspect the fuel system components for any signs of fuel leaks or other damage. If the engine does not start or there are indications that air remains in the fuel system, repeat the bleeding process at the fuel filter or fuel injectors.
Consider replacing your current primary fuel filter with an AirDog® fuel system to reduce the likelihood of having to bleed air from your fuel system in the future. AirDog® fuel systems are more forgiving of procedural mistakes and make easy work of priming the fuel system after fuel filter changes.
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Inspect injectors
Inspecting the injectors is a crucial step in troubleshooting a Detroit Diesel 671 engine that won't start, even after replacing the fuel pump, filter, and lines. Here are some detailed instructions on how to inspect the injectors:
Identify the Injector:
Locate the injector by following the fuel lines from the fuel pump. Each Detroit Diesel 671 engine uses both short and long fuel lines, so be sure to identify the correct injector. The injector will have a circular plate with a 2- to 4-digit number, possibly starting with a letter (e.g., N55, N65).
Check for Fuel Circulation:
Before removing any components, it is essential to determine if fuel is reaching the injector. One way to do this is to remove the outlet fuel jumper from the injector, as suggested by 'Birken' in the Smokstak forum. Have a rag handy to clean up any diesel fuel that may drip out. If fuel circulates into the system, it indicates that the injector is receiving fuel.
Inspect for Clogs or Damage:
If there is no fuel circulation, the injector may be clogged or damaged. In this case, remove the injector for further inspection and cleaning. Check the injector for any physical damage, such as cracks or leaks.
Clean or Replace the Injector:
If the injector is clogged, cleaning it may resolve the issue. Refer to manufacturer guidelines or seek expert advice for proper cleaning techniques. If the injector is damaged beyond repair, it will need to be replaced with an appropriate replacement injector, ensuring it matches the part number from the circular plate.
Test the Injector:
After cleaning or replacing the injector, test it to ensure proper functioning. Refer to the engine's manual for specific testing procedures. This may involve cranking the engine and observing fuel circulation through the injector, as suggested by a user in the Smokstak forum.
Remember to exercise caution when working with diesel fuel and injectors, and always refer to manufacturer guidelines or seek expert advice when in doubt.
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Check the coupler
When troubleshooting a Detroit Diesel 671 engine that won't start, one of the first things to check is the coupler. A broken coupler is often the culprit when the fuel pump is not delivering any fuel. This can be due to air or another substance in the lines, preventing the engine from starting.
To check the coupler, begin by inspecting the fuel lines for any signs of damage or deterioration. If the fuel lines are rubber and appear old, they may have internally collapsed, restricting fuel flow. Next, examine the pump seals for any leaks. Fuel weeping out of an unplugged weep hole indicates a faulty seal.
In addition to checking the coupler, it is important to verify fuel circulation in the system. One way to do this is by removing the outlet fuel jumper from the injector. Have a rag handy to clean up any spilled diesel fuel. If there is no fuel circulating, the issue could be related to the coupler or other components such as the fuel lines, pump seals, or the relief valve.
Another factor to consider is the presence of an air shut-off damper, which is a safety feature designed to shut down the engine in the event of a runaway engine. Ensure that this damper is functional and easily accessible before attempting to start the engine. It is crucial to prioritize safety when working on the Detroit Diesel 671 engine to prevent any potential hazards.
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Frequently asked questions
To remove the fuel pump from a Detroit Diesel 671 engine, you must first drain the engine oil to avoid spills and contamination. Then, carefully remove the bolts that secure the oil pan to the engine block. Unbolt the oil pan using a wrench and set it aside. This will provide access to the fuel pump, which can then be unbolted and removed.
You will need a wrench set, torque wrench, feeler gauge, puller tools, solvent for cleaning, and a suitable container for parts and small components.
Some common issues include weak fuel pressure, air leaks in the fuel lines, faulty injectors, and a weak starter.
If the fuel pump is not delivering any fuel, the coupler for the pump may be broken. Check for any leaks and inspect the fuel lines for any damage or internal collapse.
Here are some troubleshooting steps to try:
- Check for air leaks in the fuel lines.
- Bleed the fuel system of any air using the bleed screws on the fuel filter and injectors.
- Inspect the injectors and ensure they are clean and functioning properly.
- If it's cold, verify that the glow plugs are working.
- Check all electrical connections to the fuel pump and injectors.
- Examine the starter and confirm it is engaging correctly.
