DIAGNOSIS AND TESTING - FUEL TRANSFER PUMP PRESSURE
The following tests will include: pressures tests of fuel transfer pump (engine running and engine cranking), a test for supply side restrictions, and a test for air in fuel supply side.
Refer to Fuel Transfer Pump Description/Operation for an operational description of transfer pump.
The fuel transfer (lift) pump is located on left side of engine and above starter motor (Fuel Transfer Pump Location).
An improperly operating fuel transfer pump, a plugged or dirty fuel filter, or a defective overflow valve can cause low engine power, excessive white smoke and/or hard engine starting.
Before performing following tests, inspect fuel supply and return lines for restrictions, kinks or leaks.
Fuel leaking from pump casing indicates a leaking pump which must be replaced.
Pressure Test: Because the transfer pump is operating at two different pressure cycles (engine running and engine cranking), two different pressure tests will be performed.
- Remove protective cap at test port (Fuel Pressure Test Port Fitting). Clean area around cap/fitting before cap removal.
- Install Special Fuel Pressure Test Gauge 6828 (or equivalent) to fitting at test port (Fuel Pressure Test Port Fitting).
- To prevent engine from starting, remove fuel system relay (fuel injection pump relay). Relay is located in Power Distribution Center (PDC). Refer to label under PDC cover for relay location.
- Using key, crank engine over while observing gauge. Pressure should be 5-7 psi.
- Re-install fuel system relay to PDC.
- Start engine and record fuel pressure. Pressure should be a minimum of 69 kPa (10 psi) at idle speed.
- Because fuel pump relay was removed, a Diagnostic Trouble Code (DTC) may have been set. After testing is completed, and relay has been installed, use DRB scan tool to remove DTC.
Fuel Supply Restriction Test:
Due to very small vacuum specifications, the DRB scan tool along with the Periphal Expansion Port (PEP) Module and 0-15 psi transducer must be used.
- Verify transfer pump pressure is OK before performing restriction test.
- Locate and disconnect fuel supply line quick-connect fitting at left-rear of engine (Fuel Return and Supply Line Quick-Connect Locations). After disconnecting line, plastic clip will remain attached to metal fuel line at engine. Carefully remove clip from metal line. Snap same clip into fuel supply hose.
- Install Special Rubber Adapter Hose Tool 6631 (3/8") into ends of disconnected fuel supply line.
- Install transducer from PEP module to brass "T" fitting on tool 6631.
- Hook up DRB scan tool to transducer.
WARNING: DO NOT STAND IN LINE WITH THE COOLING FAN FOR THE FOLLOWING STEPS.
- Start engine and record vacuum reading with engine speed at high-idle (high-idle means engine speed is at 100 percent throttle and no load). The fuel restriction test MUST be done with engine speed at high-idle.
- If vacuum reading is less than 6 in/hg. (0-152 mm hg.), test is OK. If vacuum reading is higher than 6 in/hg. (152 mm hg.), restriction exists in fuel supply line or in fuel tank module. Check fuel supply line for damage, dents or kinking. If OK, remove module and check module and lines for blockage. Also check fuel pump inlet filter at bottom of module for obstructions.
Testing For Air Leaks in Fuel Supply Side:
- A 3-foot section of 3/8" I.D. clear tubing is required for this test.
- Using a tire core valve removal tool, carefully remove core valve from inlet fitting test port.
- Attach and clamp the 3/8"clear hose to fitting nipple.
- Place other end of hose into a large clear container. Allow hose to loop as high as possible above test port.
- The fuel transfer pump can be put into a 25 second run (test) mode if key is quickly turned to crank position and released back to run position without starting engine.
To prevent engine from starting in this test, first remove fuel system relay (fuel injection pump relay). Relay is located in Power Distribution Center (PDC). Refer to label under PDC cover for relay location.
Because fuel pump relay was removed, a Diagnostic Trouble Code (DTC) may have been set. After testing is completed, and relay has been installed, use DRB scan tool to remove DTC.
- Allow air to purge from empty hose before examining for air bubbles. Air bubbles should not be present.
- If bubbles are present, check for leaks in supply line to fuel tank.
- If supply line is not leaking, remove fuel tank module and remove filter at bottom of module (filter snaps to module). Check for leaks between supply nipple at top of module, and filter opening at bottom of module. Replace module if necessary.
- After performing test, install core back into test fitting. Before installing protective cap, be sure fitting is not leaking.