1990 Isuzu Impulse AutomaticFACTORY OEM SERVICE PROCEDURE

Fuel Pump Relay

  1. ECM powers relay as long as ECM receives ignition reference signals or starter crank signal. For fuel pump relay location, see FUEL PUMP RELAY LOCATION  table.
  2. To run fuel pump without starting engine, remove relay and jumper terminals No. 2 and 4. See Figure & Figure .
  3. To test relay, use jumper wires to ground terminal No. 4 of relay and apply battery voltage to terminal No. 2 of relay. Using ohmmeter, check for continuity between relay terminals No. 1 and 3. If continuity is not present, replace relay.
FUEL PUMP PERFORMANCE

Application Unregulated Pressure: psi (kg/cm2 ) Regulated Pressure: psi (kg/cm2 )
Amigo, Pickup & Trooper 2.6L (1) 42 (3.0) (2) 35 (2.5)
Impulse (3) 35-38 (2.5-2.7) 25-30 (1.8-2.1)
Trooper 2.8L N/A (3) 9-13 (.62-.91)
(1) There are two unregulated pressure tests. The first is with fuel pressure regulator and pressure regulator Vacuum Switching Valve (VSV) vacuum hoses disconnected. The second is with pressure regulator vacuum hose connected, Blue wire of VSV is connected to positive battery terminal and Black wire connected to negative battery terminal. In both tests, pressure should be as specified.
(2) With vacuum hose connected to fuel pressure regulator and fuel pressure regulator Vacuum Switching Valve (VSV) disconnected.
(3) With engine running and vacuum hose disconnected from pressure regulator.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.