Chrysler Full-Size Trucks 1989-1996 Repair Guide

Injectors

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GENERAL INFORMATION



See Figure 1

The fuel injectors are mounted on the left side of the cylinder head and are connected to the fuel pump by the high pressure fuel lines.



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Fig. Fig. 1: The injector is a precise one-way valve that sprays a metered amount of fuel at high pressure into the combustion chamber

The injectors consist of the nozzle holder, O-ring, water seal, shims, spring, needle valve and nozzle. Fuel enters the injector through the top of the injector (fuel inlet) and is routed to the needle valve bore. The injector fires when fuel pressure rises to an amount sufficient to overcome the needle valve spring tension. For 1989-93 models, this pressure is 3,550 psi (24,65 kPa). For 1994-96 models, the pressure needed to overcome the needle valve spring tension is a little higher at 3,822 psi (26,252 kPa). This pressure is commonly known as the "pop'' pressure.

As the needle valve opens, fuel flows rapidly through the spray holes in the nozzle tip into the combustion chamber. After this injection, the fuel pressure drops and the needle valve is closed preventing further fuel flow, and conversely, exhaust flow into the injector.

REMOVAL & INSTALLATION



See Figures 2, 3, 4, 5 and 6

  1. Disconnect the negative battery cable. Remove the throttle linkage and bracket if necessary.
  2.  
  3. Disconnect the high pressure fuel supply line to the injector.
  4.  
  5. Disconnect the fuel drain manifold.
  6.  



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Fig. Fig. 2: Fuel is supplied to the six diesel fuel injectors by individual high pressure lines



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Fig. Fig. 3: Unscrew and remove the diesel fuel injector

  1. Clean the area around the injector.
  2.  



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Fig. Fig. 4: Use a wire brush to clean the injector bore as shown

Certain types of injectors MAY have an O-ring located above the hold-down nut.



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Fig. Fig. 5: Use only one copper washer on the diesel injector

  1. Using the correct deepwell socket, remove the injector from the cylinder head.
  2.  

To install:


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Fig. Fig. 6: Install the diesel injector so that its tab is aligned with the notch in the bore

  1. Clean the injector bore with a bore brush.
  2.  
  3. Assemble the injector and 1 new copper sealing washer. Never use more than 1 copper washer.
  4.  
  5. Apply a thin coat of anti-seize compound to the threads of the injector hold-down nut and between the top of the nut and the injector body.
  6.  
  7. Align the protrusion in the injector with the notch in the bore and install the injector. Tighten the injector retainer nut to 6 ft. lbs. (60 Nm).
  8.  
  9. Push the O-ring into the groove at the top of the injector, if applicable.
  10.  
  11. Using new sealing washers, assemble the fuel drain manifold and high pressure lines. Tighten the banjo fitting bolt to 6 ft. lbs. (8 Nm). Leave the high pressure line loose temporarily.
  12.  


CAUTION
Do not place any part of the hand near the base of the high pressure line. A fuel leak from a high pressure fuel line has sufficient pressure to penetrate the skin and cause serious bodily harm. Do not bleed the lines if the engine is hot. Fuel spilling onto a hot exhaust manifold creates the danger of fire.

  1. To bleed air from the system, run or crank the engine and tighten the fitting after the air has expelled. If more than 1 injector was replaced, tighten each fitting after the air has expelled before going on to the next injector fitting. Tighten the fittings for 1989-93 models to 18 ft. lbs. (24 Nm) and 1994-96 models to 22 ft. lbs. (30 Nm). The operation is complete when the engine runs smoothly. If the air cannot be removed, check the pump and supply line for suction leaks.
  2.  
  3. Install the throttle linkage and bracket if they were removed.
  4.  

TESTING



See Figures 7 and 8


CAUTION
If examining for leaks, use a sheet of cardboard to show any spraying fuel. Do not use your hand and wear safety goggles. The extremely high pressure can cause serious personal injury, especially to your skin and eyes.

A leaking fuel injector can cause fuel knock, poor performance, black smoke, poor fuel economy and rough engine idle. If the needle valve does not operate properly, the engine may misfire and produce low power.

A leak in the injection pump-to-injector high-pressure fuel line can cause many of the same symptoms as a malfunctioning injector. First check the lines before the injectors.



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Fig. Fig. 7: Loosen the fittings one at a time, to check the effect on engine rpm-no change in rpm indicates a faulty injector

  1. To check the injectors, start the engine and loosen the high-pressure line nut one-at-a-time at each injector. Listen for a decrease in engine speed.
  2.  



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Fig. Fig. 8: Use a tester like the one shown to measure pop pressure for the diesel fuel injector

  1. If the engine speed drops, the injector is operating normally. If the engine speed remains the same, the injector is malfunctioning. After testing each injector, tighten the line nuts for 1989-93 models to 18 ft. lbs. (24 Nm) and 1994-96 models to 22 ft. lbs. (30 Nm).
  2.  
  3. If an injector is found to be malfunctioning, remove it and test it on a standard bench-mount injector tester. Follow the manufacturer's instructions for bench testing the injector.
  4.  
  5. If the opening (pop) pressure is below specifications, replace the injector. For 1989-93 models, this pressure is 3,550 psi (24,65 kPa). For 1994-96 models, the pop pressure is 3,822 psi (26,252 kPa).
  6.  

 
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