LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mazda >> 2003 >> B4000 Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> System Tests >> Fuel Delivery System
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Fuel Delivery System

  1. Check System Integrity -  Visually inspect entire fuel delivery system. Check fuel lines, connections, relays, fuel tank, fuel pump, fuel pulse damper and fuel injectors for leaks, looseness, cracks, kinks or pinching. Inspect fuel system for possible collision damage. Visually inspect electrical wiring harnesses and connectors. Check for loose pins, corrosion, abrasions and other damage. Inspect electrical system for possible collision damage. Verify vehicle has been maintained. Verify Inertia Fuel Shutoff (IFS) switch is set (on). Verify battery voltage is 12.5 volts or more. Check integrity of fuses. Verify fuel level is sufficient. If any problems are identified, repair as necessary. After repair, rerun QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If no problems are found, go to next step.
  2. Check For Voltage At Fuel Pump Harness Connector -  Using scan tool, verify IFS switch state. Perform fuel pump shutoff switch reset procedure. See INERTIA FUEL SHUTOFF SWITCH under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING - B2300, B3000, B4000 & TRIBUTE article. Disconnect fuel pump 4-pin harness connector at fuel pump. With KOEO, connect a DVOM between fuel pump power circuit (Pink/Black wire) and fuel pump ground (Black/Yellow wire) at fuel pump 4-pin harness connector. Enter OUTPUT TEST MODE and turn on fuel pump circuit. Monitor voltage reading. If voltage reading is more than 12.5 volts, exit OUTPUT TEST MODE. Reconnect fuel pump 4-pin harness connector. Restore vehicle to original condition. Go to next step. If voltage reading is 12.5 volts or less, check for opens and shorts in fuel pump power and ground circuits. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. Restore vehicle.
  3. Check Fuel Filter For Proper Maintenance -  Locate and inspect vehicle maintenance records. Check last service date. If fuel filter was replaced within the last 1000 miles, go to next step. If fuel filter was not replaced within the last 1000 miles, replace fuel filter. After repair, go to next step.
  4. Check Fuel Pressure -  Release fuel pressure. See FUEL PRESSURE RELEASE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. With KOEO, using scan tool, access Output Test Mode. Run fuel pump to obtain maximum fuel pressure. Fuel pump will run for about 8 seconds when Output Test Mode is selected and activated. If fuel pressure is 56-72 psi (389-499 kPa), go to step  5 . If fuel pressure is not 56-72 psi (389-499 kPa):
    • For fuel pressure more than 72 psi (499 kPa), replace faulty fuel pump. After repair, restore vehicle to original condition. Recheck fuel pressure.
    • For fuel pressure less than 56 psi (389 kPa), go to step  7 .
  5. Check Fuel Injector Flow & Leakage -  Using a fuel injector tester, flow test fuel injectors following equipment manufacturers instructions. See FUEL INJECTOR FLOW RATE SPECIFICATIONS  table. If flow rate values are within specification, verify no other leak is present. Replace faulty fuel pump. If flow rate values are not within specification, replace faulty fuel injector(s). Restore vehicle to original condition. After repair, recheck fuel pressure and go to next step.
    FUEL INJECTOR FLOW RATE SPECIFICATIONS

    Engine Lbs. Hr. (kg/hr)
    2.3L 21 (9.6)
    3.0L 12 (5.5)
    4.0L 19 (8.7)
  6. Check Pulse Damper Diaphragm -  Install fuel pressure gauge. Start engine and idle for 10 seconds. Turn ignition off. Wait 10 seconds. Start engine again and idle for 10 seconds. Turn ignition off. Disconnect pulse damper vacuum hose. Inspect for fuel in vacuum hose and pulse damper port. If vacuum hose and pulse damper port are free from fuel contamination, go to next step. If vacuum hose and pulse damper port are not free from fuel contamination, replace components as necessary.
  7. Check Fuel Supply Line For Restriction -  Disconnect fuel supply line at fuel rail and fuel pump. Inspect fuel supply line for restrictions. Apply 3-5 psi (21-34 kPa) regulated air pressure to fuel supply line. Observe air flow. If air flows freely, replace faulty fuel pump. If air does not flow freely, repair fuel supply line restriction. Restore vehicle to original condition. After repair, recheck fuel pressure.
scientia non olet · About LEMON Manuals