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Home >> Mercedes Benz >> 1992 >> 400E >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Testing >> Fuel Delivery & System Pressures - Gasoline >> Fuel Pump Pressure
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Fuel Pump Pressure

  1. Remove plastic protective cover from fuel pump(s). Unscrew test cap on end of fuel pump No. 1. Using Line Fitting Adapter (103-589-02-63-00), connect Fuel Pressure Gauge (103-589-00-21-00) to fuel pump.
  2. For V8 engines, remove fuel pump relay (under hood near fuse panel). Bridge fuel pump relay connector socket terminals No. 7 and No. 8 with jumper wire to establish fuel pressure. See Figure .
  3. For 4 and 6-cylinder engines, remove MAS unit from underhood component compartment area, near CIS-E control unit. To remove MAS unit, turn top knob from position No. 1 to position No. 0 and lift/pull MAS unit out of electrical connector socket. Using fused jumper wire, jumper connector pin socket No. 2 with battery voltage source to establish fuel pressure.
  4. Read fuel pressure on gauge. Pressure should be 29-58 psi (2-4 kg/cm2 ). If pressure is less than 29 psi (2 kg/cm2 ), fuel pump No. 1 is defective. If pressure is greater than 58 psi (4 kg/cm2 ), fuel pump No. 2 is defective.
  5. When testing is completed, remove pressure gauge, reconnect fuel pump test cap and tighten to 88-106 INCH lbs. (10-12 N.m). Install fuel pump relay or MAS unit. To install MAS unit, push MAS unit into electrical connector socket and turn top knob from position No. 0 to position No. 1.
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