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HOMESERVICE MANUALSJEEP1987WAGONEER BASE, 2.5 H, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEM2.5L TBI SYSTEMOPERATIONFUEL CONTROL
1987 Jeep Wagoneer Base, 2.5 H, Automatic

Fuel Control

1987 Jeep Wagoneer Base, 2.5 H, AutomaticSECTION Fuel Control

An electric in-tank fuel pump supplies fuel through the fuel filter located under the right rear floor pan to the throttle body, maintaining a constant operating pressure. Fuel enters the fuel bowl reservoir of the throttle body through the injector and overflow type fuel pressure regulator. The fuel pump is controlled by the ECU. A ballast resistor attached to the right side of the plenum chamber, reduces fuel pump speed after engine is running. The resistor is by-passed in the "Start" position.

The fuel injector and fuel pressure regulator are integral components of the throttle body. The injector is electronically controlled by the ECU. See Fig 1 .

Fig 1: Cross Section View of Injector
G11210

The fuel pressure regulator is a diaphragm-operated relief valve which maintains fuel pressure of 17.3 psi (1.2 kg/cm2 ). See Fig 2 . Fuel in excess of this pressure is returned to fuel tank by a fuel return line. The regulator is not controlled by the ECU. The regulator's spring chamber is vented to the same pressure as the tip of the injector.

Fig 2: Cross Section View of Fuel Pressure Regulator
G11211

Since fuel pressure at the injector is kept constant, the volume of fuel injected is dependent only on the length of time that the injector is energized. The injection time duration is based on engine operating conditions, which are provided to the ECU by the input sensors. During engine start-up, the injector delivers an extra amount of fuel to aid in starting.

RENDER: 1.0x

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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.