'tiny airleak' here, tiny air leak there,, one is all it takes...
'Lift pump pumps pretty much exactly 0.25 liter in 15 seconds, measured after the stock fuel filter before the hard line going to the IP.'
• If more than 0.24 liters (½ pint) in 15 seconds, refer to Fuel Lift Pump Pressure Check.
• If less than 0.24 liter (½ pint) in 15 seconds, refer to Fuel Lift Pump Suction Line Check.
IMO, thats a tail err fail, definitely a sign. It should be nearly double that with a healthy unrestricted lift pump receiving full voltage.
Stalling and other symptoms your describing are ALL classic sign of fuel STARVATION. All Im saying..
Grab a donut and a large cup of coffee, enjoy the show....
Fuel Tank Components
FILLER CAP
The filler cap contains a 2-way check valve. This will allow air to escape during the day when the tank heats up. In the event of a rollover, the valve will prevent spillage. Under pressure, no greater than 2 psi will exist. The valve must also allow air to enter the tank to replace the fuel used by the engine. A vacuum of no more than about one inch of mercury can accumulate in the tank and a slight hissing sound when removing the cap is normal. The fuel system is calibrated with the cap in place and any alterations will effect performance. Diesel fuel tank caps are specific to Diesels. Gasoline tank caps may fit in the diesel tank filler neck but should not be used.
FUEL PICKUP AND SENDING UNIT
See Figure 4-4. The fuel pick up, commonly known as the “ sock” has three functions:
1. Strain out large solids.
2. Act as a strainer to prevent entry of water.
3. Act as a wick to drain fuel down to the bottom of the tank since all pickup pipes do not reach the very bottom of the tank.
The tank filter is a Saran (Polyvinylidene Chloride) sock and is fastened to the fuel inlet line of the in-tank fuel filter and fuel pick-up assembly.
The fuel tank filter sock has a bypass valve which opens when the filter is covered with wax allowing fuel to flow to the fuel heater.
Without this sock fuel line heater would be ineffective because the fuel would be trapped in the tank. Since the bypass valve is located at the upper end of the sock, fuel will only be drawn into the waxed sock if the tank contains more than approximately 4 gallons of fuel. Therefore, it is important to maintain a minimum of 1/4 tank of fuel when temperatures are below 20 degrees F.
The Saran sock material has a nominal pore size of 130 microns. In addition to acting as a particle filter for the mechanical lift pump, the Saran tank filter acts as a wick to pick up fuel from the bottom of the tank and as a water filter; water is excluded on the basis of the difference in surface tension between the water and the sock material on the one hand and the fuel and the sock material on the other.
The fuel pickup tube doesn’t reach the bottom of the tank. However, since the sock acts as a “wick” the fuel level can actually be lower than the level of the tube and fuel will be drawn out right down to empty. Also, with this design, the level of water in the tank can be much higher before water enters the fuel system. This is about five gallons. Water that gets into the tank will eventually be absorbed by good fuel and will pass harmlessly through the fuel system. Water will be absorbed at a rate of about one gallon per 1000 miles.
— IMPORTANT —
If the gas unit is installed on a diesel, it will cause intermittent problems with idle and power loss.
Let me interject this quickly. Emphasis added- Thats why you shouldn't delete the strainer. Going strainer-less allows natural condensation to coaleces into water droplets that collect and stew into a brew of toxic and most corrosive sewage at the bottom of the tank.. Theres a picture of a fuel tank 'round here that clearly shows the end results of going naked. Do be afraid..
Point being.. Make sure the proper strainer is in place. Common for new aftermarket fuel sender to come preassembled with the incorrect 'gasoline sock' aka a diesel choker. Dont asume anything at this point. On with the show..
[FONT=Arial,Bold]Lift Pump[/FONT]
The lift pump is designed to move fuel under a low (suction) pressure from the fuel tank and deliver it through the filter to the transfer pump inside the fuel injection pump. In order for the lift pump to operate correctly the fuel tank must have fuel, the lines between the tank and pump must not have leaks, and the fuel fill cap must be operating properly.
If a failure occurs in the operation of the lift pump, the customer may complain about a no-start, stall or low power condition. The injection pump must have a continuous supply of fuel without the presence of excessive air bubble in order to operate correctly.
[FONT=Arial,Bold][FONT=Arial,Bold]Fuel System Related Services[/FONT][/FONT]
[FONT=Arial,Bold]Fuel Supply System Check
[/FONT]If the fuel supply system is not delivering enough fuel or air is being drawn into the fuel injection system, driveability could be greatly affected 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 checks should be performed:
• Make certain that there is sufficient fuel in the tank.
• Check for air leaks or restrictions on the suction side of the fuel lift pump.
• Check for restrictions in the fuel return system.
• Check for leaks at all of the fuel connections from the fuel tank to the injection pump.
• 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 to prevent engine starting.
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 or energize the lift pump and measure the amount of fuel:
• If more than 0.24 liters (½ pint) in 15 seconds, refer to Fuel Lift
Pump Pressure Check.
• If less than 0.24 liter (½ pint) in 15 seconds, refer to Fuel Lift Pump
Suction Line Check.
[FONT=Arial,Bold]Fuel Lift Pump Suction Line Check
[/FONT]1. Remove the fuel tank cap and repeat the Lift Pump Flow Check.
• If the flow is more than 0.24 liter (½ pint) in 15 seconds, replace the defective fuel tank cap.
• If the flow is less than 0.24 liter (½ 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 (½ pint) in 15 seconds, refer to Fuel System Air Leak Check.
• If the flow is less than 0.24 liter (½ 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 Electrical Circuit Diagnosis.
6. Attach the lift pump suction line to the fuel sender.
[FONT=Arial,Bold]Fuel Lift Pump Pressure Check
[/FONT]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 Electrical 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.
[FONT=Arial,Bold]Fuel System Air Leak Check
[/FONT]
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.
4. Check the fuel sender for air leakage.
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. (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 Return System Restriction Check
1. Disconnect the hose of the fuel return line at the fuel sender.
2. Disconnect the hose of the fuel return line at the injection pump and connect a vacuum pump with gauge to the hose.
3. Apply vacuum to the return line and observe the gauge reading.
• If vacuum does not build and hold, go to Step 4.
• If vacuum builds and holds, repair the return line restriction.
4. Connect the fuel return line at the injection pump and fuel sender.
5. Clean any fuel spillage.
6. Run the engine to check for fuel leakage.
Note; If excessive water or fungi/bacteria are present at the fuel filter, you must perform a fuel system cleaning. This is a lengthy procedure, but it must be performed thoroughly in order to be affective.