GM/Detroit 6.5L ENGINE CONTROLS – Fuel Tank Leak Check

The diagnosis of fuel odor may be a condition of leaking fuel tank, filler neck or filler cap. A defective filler cap, a plugged or pinched vent pipe can cause a collapsed fuel tank. Loose mounting straps or foreign material in tank may be the cause of a rattle at the fuel tank.

Leak Check Procedure
Caution : Place a dry chemical (Class B ) fire extinguisher near the area before performing a Fuel Tank Leak Check. Before removing the fuel tank for a suspected leak, make sure that the fuel pipes or the tubes are not leaking on to the tank. Once removed, make sure that the fuel is not leaking around the fuel sender O -rin g. Failure to follow the sepre cautions may result in personal injury.

This check requires the fuel sender and the o-ring to be installed.
1. Disconnect the battery cables.
2. Drain the fuel tank (refer to Fuel Tank Draining Procedure.
3. Remove the fuel tank (refer to Fuel Tank Replacement).
4. Cap the fuel feed tube and the fuel return tube on the fuel sender.
5. Connect a piece of hose to the filler tube nipple and plug the opposite end.
6. Submerge the tank in water or apply a soap solution to the outside of the tank.
7. Apply 35 kPa (5 psi) of air pressure to the vent hose of the fuel tank (a leak will show up as bubbles).

Contamination Testing
Fungi and 6ther microorganisms can survive and multiply in diesel fuel if water is present. The fungi can be present in any part of the fuel handling system.
These fungi grow into long strings and will form into large globules. The growths appear slimy and are usually black, green, or brown. The fungi may grow anywhere in the fuel but are most plentiful where diesel fuel and water meet. As the fuel is agitated (when service station tanks are being filled), fungi are distributed throughout the tank and may be pumped into a vehicle.
Fungi use the fuel as their main energy supply and need only trace amounts of water and minerals. As they grow and multiply, they change fuel into water, sludge, acids, and products of metabolism. The most common symptom is fuel filter plugging; however, various metal components (fuel tank, pipes, and injection pump) can corrode.

Caution : Avoid physical contact with the biocides in order to avoid personal injury.
If fungi have caused fuel system contamination, use a diesel fuel biocide to sterilize the fuel system. Do not exceed the dosage recommended on the label. Discontinue the use of a biocide when towing a trailer.

It is permissible to have biocide in the fuel when starting to tow, but do not add any biocide while towing. Steam cleaning may be necessary if most of the fungus growth cannot be removed with biocides. The presence of water or gasoline in diesel fuel may also cause injection pump and nozzle damage. This procedure checks for the presence of water and gasoline in diesel fuel that may cause injection pump and nozzle damage.
Remove the fuel filter element and inspect it.
• If water, gasoline or fungi/bacteria are not present, end the inspection.
• If water or fungi/bacteria are present, Go to Cleaning Water from the Fuel System.
• If gasoline is present, Go to Cleaning Gasoline from the Fuel System.

Cleaning Water from the Fuel System
1. Disconnect the batteries.
2. Drain the fuel tank.
3. Remove the fuel tank (Refer to Fuel Tank Replacement).
4. Remove the fuel sender unit (Refer to Fuel Sender Assembly Replacement).
5. Inspect the fuel tank and the fuel sender for rust, fungi or bacteria.
6. Clean the inside of the fuel tank and the fuel sender with hot water.
7. Use compressed air in order to dry the fuel tank and the fuel sender.
8. Disconnect the ends of the following lines:
• The lift pump suction line
• The lift pump feed line
• The fuel filter outlet line
• The fuel filter drain line
• The fuel return line
9. Inspect each of the pipes.
10. Replace any rusted pipes.
11. Clean the inside of the fuel filter housing.
12. Dry the fuel filter housing with compressed air.
13. Dry the inside of each line with low pressure air.
14. Remove the ECM 1 fuse from the underhood relay center.
15. Install a new fuel filter element.
16. Install the fuel sender and the fuel tank (add clean diesel fuel to V a full).
17. Reconnect the following lines:
• The lift pump suction (both ends) lines.
• The lift pump feed (both ends) lines.
• The fuel filter drain line.
• The fuel return (at the injection pump) line.
18. Connect the fuel filter outlet and the fuel return line at the fuel sender to the hoses that flow to the metal containers.
19. Connect the batteries.

20. Use the scan tool in order to command the lift pump ON.
21. Operate the lift pump until clean fuel flows from the fuel filter outlet into a metal container.
22 . Connect the hose from the fuel filter outlet to the injection pump inlet.
23. Open each injection line at its nozzle end and crank the engine until clean fuel flows from it.
• Use two wrenches when loosening the injection line fittings.
• Allow a maximum of 15 seconds cranking time, followed by 1 minute of cranking motor cooling time.
24. Tighten each injection line fitting at its nozzle. Use two wrenches when tightening the injection line fittings.
25. Install the ECM 1 fuse in the underhood relay center.
26. Start and run the engine for 1 minute while the fuel flows from the fuel return line into a metal container.
27. Stop the engine.
28. Connect the fuel return hose to the fuel sender.
29. Clean any fuel spillage from the engine.
30. Fill the fuel tank and add a biocide, if needed.

Cleaning Gasoline from the Fuel System
1. Drain the fuel tank.
2. Fill the fuel tank.
3. Remove the ECM 1 fuse from the underhood relay center.
4. Remove the fuel filter outlet and connect it.to a hose that flows to a metal container.
5. Use a scan tool and command the lift pump ON until clean fuel flows from the fuel filter outlet into a metal container.
6. Connect the hose from the fuel filter outlet to the injection pump inlet.
7. Install the ECM 1 fuse into the underhood relay center.
8. Attempt to start and run the engine for 15 minutes (If engine does not start, purge the injection system).
9. Stop the engine.
10. Clean any fuel spillage from the engine.
11. Clear the engine of any DTCs.

Fuel Quality Diagnosis
Fuel qual ity may cause driveability problems such as hesitation, lack of power, stall, no start, etc.
For best results, use Number 2-D diesel fuel year-round (above and below freezing conditions) as oil companies blend Number 2-D fuel to address climate differences. Number 1-D diesel fuel may be used in very cold temperatures (when it stays below -18°C (0°F); however; it will produce a power and fuel economy loss. The use of Number 1-D fuel in warm or hot climates may result in stalling, poor starting when the engine is hot and may damage the fuel injection system.

Specific Gravity Testing
The fuel quality hydrometer provides a general indication of fuel quality and should not be considered scientifically accurate.

1. Drain the fuel filter housing by following the steps below:
1.1. Stop the engine.
1.2. Place a container under the water drain valve exit hose at the left front side of the engine.
1.3. Open the drain valve.
1.4. Use a scan tool and command the fuel lift pump ON.
1.5. Fill a 1 liter (0.946 quart) container with a sample of fuel.
1.6. Close the drain valve.
2. Obtain a fuel quality hydrometer (J 38641-B).
3. Fill the hydrometer with the fuel sample by doing the following:
3.1. Squeeze the hydrometer bulb.
3.2. Submerse the hydrometer tip into the sample.
3.3. Release the bulb, allowing fuel to enter the glass tube until it completely floats the glass bulb inside the tube.
3.4. Gently spin the hydrometer to relieve the surface tension of the fuel sample. Read the scale on the glass bulb at the point where the top of the fuel sample contacts it. By reading this value, it will give an approximate fuel oil specific gravity. Refer to tool instructions on how to determine API Gravity.
4. Refer to Fuel Oil Specific Gravity Requirements table. If the correct fuel is being used in the conditions listed in Fuel Quality, and meets number 1-Diesel or number 2-Diesel fuel oil specific gravity requirements, fuel is OK. If not, the fuel should be replaced.

Fuel Sender Diagnosis
The fuel sender should be checked for return restrictions. For diagnosis of the pickup tube, refer to Fuel Return System Diagnosis.

Fuel Strainer
The strainer is self cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water and should be thoroughly cleaned.

Fuel Supply System Check
If the fuel supply system is not delivering enough fuel, or air is being drawn into the fuel injection system, driveability could be greatly effected or a Cranks But Will Not Run symptom could exist. If another diagnosis indicates, or if the fuel supply system is suspected of not delivering enough fuel or drawing air, the following systems should be checked.
• Air leaks or restrictions on the suction side of the fuel pump will seriously affect pump output.
• Restriction in the fuel return system.
• Make certain that there is sufficient fuel in the tank.
• Check for leaks at all of the fuel connections from the fuel tank to the injection pump.
• Tighten any loose connections.
• With the engine running, check all of the hoses and the lines for flattening or kinks that would restrict the flow of fuel.

Fuel Lift Pump Flow Check
1. Remove the ECM 1 fuse from the underhood relay center.
2. Disconnect the pipe at the lift pump outlet fitting.
3. Install a hose at the lift pump outlet fitting and place a 1 liter (0.946 quart) container at the hose in order to collect fuel.
4. Crank the engine and measure the amount of fuel.
• If more than 0.24 liter (1/> pint) in 15 seconds, refer to Fuel Lift Pump Pressure Check.
• If less than 0.24 liter (V 2 pint) in 15 seconds, refer to Fuel Lift Pump Suction Line Check.

Fuel Lift Pump Suction Line Check
1. Remove the fuel tank cap and repeat the Lift Pump Flow Check.
• If the flow is more than 0.24 liter (1A> pint) in 15 seconds, replace the defective fuel tank cap.
• If the flow is less than 0.24 liter (V 2 pint) in 15 seconds, go to the next step.
2. Separate the lift pump suction line from the fuel sender.
3. Connect the suction line to a source of clean fuel by using an additional hose.
4. Repeat the Lift Pump Flow Check.
• If the flow is more than 0.24 liter (V2 pint) in 15 seconds, go to Fuel System Air Leak Check.
• If the flow is less than 0.24 liter (V 2 pint) in 15 seconds, Go to Step 5.
5. Check the lift pump suction line for a restriction.
• If a restriction exists, repair it and recheck lift pump flow.
• If no restriction exists, replace the lift pump and recheck the lift pump flow. Refer to Fuel Pump Relay Circuit Diagnosis.
6 . Attach the lift pump suction line to the fuel sender.

Fuel Lift Pump Pressure Check
1. Install a tee adapter at the injection pump.
2. Connect a pressure gauge with the dial indication of 0-103 kPa (0 to 15 psi) to the tee adapter.
3. Start the engine and measure the fuel pressure.
• If the fuel pressure is a least 4 psi (27 kPa) continue to step 4.
• If the pressure is less than 4 psi, refer to Fuel Pump Relay Circuit Diagnosis before replacing the lift pump.
4. Remove the pressure gauge and the tee adapter.
5. Connect the inlet pipe.
6. Clean any fuel spillage
7. Operate the engine and check for any fuel leaks.

Fuel System Air Leak Check
1. Install a transparent hose between the filter outlet and the injection pump inlet.
2. Start and idle the engine, observing the fuel for air bubbles.
• If air bubbles are not present, stop the engine and Go to Step 7.
• If air bubbles are present, stop the engine and Go to Step 3.
3. Check the lift pump suction line for air leakage.
• Disconnect the fuel pipe from the fuel sender.
• Plug the fuel pipe,
• Disconnect the fuel pipe from the lift pump.
• Install a hand held vacuum pump with a gauge.
• Apply vacuum to the fuel pipe and observe the gauge reading.
– If the vacuum does not drop, connect the fuel pipe and Go to Step 4.
– If the vacuum drops, repair the air leak in the suction line and install the suction line pipe and the hose.
4. Check the fuel sender for air leakage.
• Remove the fuel tank.
• Remove the fuel sender from the fuel tank.
• Remove the strainer and plug the bottom end of the pickup tube.
• Apply a vacuum to the upper end of the pickup tube.
• Observe the gauge reading.
– If the vacuum does not drop (fuel inlet side of sender is OK), install the fuel sender and the fuel tank.
– If the vacuum drops, replace the fuel sender, install the fuel tank, connect the fuel pipe and Go to Step 5.
5. Start and run the engine.
6. Observe the fuel for air bubbles.
• If air bubbles are present, stop the engine and recheck Steps 3 and 4.
• If air bubbles are not present, stop the engine and Go to Step 7.

7. Remove the transparent hose and connect the hose of the filter outlet to the injection pump inlet fitting.
8. Disconnect the return hose at the injection pump.
9. Install a transparent hose between the injection pump and the hose of the return line.
10. Start and run the engine.
11. Observe the fuel for air bubbles.

Important: It is normal to see small amounts of bubbles during snap acceleration.
• If air bubbles are present, replace the injection pump. Refer to Fuel Injection Pump Replacement.
• If air bubbles are not present, Go to Step 12.
12. Stop the engine.
13. Remove the transparent hose and attach the fuel return hose at the injection pump.
14. Clean any fuel spillage.
15. Run the engine to check for fuel leakage.

Fuel Lift Pump Electrical Circuit
When the key is first turned ON without the engine running, the control module turns the fuel lift pump relay ON during glow plug cycle. This builds up fuel pressure quickly. If the engine is not started after the glow plug cycle, the control module shuts the fuel lift pump OFF and waits for engine rpm. As soon as the engine is cranked, the control module turns the relay ON and runs the fuel lift pump.
As a backup system to the fuel lift pump relay, the fuel lift pump is also turned ON by an oil pressure switch. When engine oil pressure reaches about 28 kPa (4 psi) through cranking, the oil pressure switch will close to complete the circuit to the fuel pump.
For the location of the fuel pump relay, refer to Engine Controls Components. For diagnosis of the lift pump electrical circuit, refer to Fuel Pump Relay Circuit Diagnosis.

Fuel Manager/Filter Diagnosis
Diagnosis of the fuel filter can be found in the Contamination Testing. For diagnosis of the Water in Fuel lamp circuit, refer to the Water-in -Fuel Lamp Circuit Diagnosis.
Diagnosis of the fuel heater can be found in the Fuel Heater Functional Diagnosis.

 

 

 

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