Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Diesel Fuel Injectors


Diesel fuel injectors are prone to plugging due to dirt or water in the system. Because diesel fuel is less refined than gasoline, there is a greater chance of pollutants getting into the fuel system. An inoperative injector can cause very poor fuel mileage, heavier than normal exhaust soot, uneven idle, loss of power and/or overheating and knocking in the cylinder. Don't mistake normal bearing clatter-a generalized noise throughout the engine-for a knocking in a specific cylinder.


See Figures 1 and 2

To perform a quick check on the injectors, run the engine at above idle speed. Wrap an absorbent rag around the pipe joint at the injector and loosen the cap nut on the injector. As the pressure in the line leaks off, the cylinder should cease firing and the engine characteristics should change.

Click image to see an enlarged view

Fig. Fig. 1: To quickly check an injector, loosen the injector and determine whether engine rpm decreases

If there is no change in engine behavior, the injector or its heat shield may be defective. Injectors cannot be repaired or disassembled; defective injectors must be replaced. If removing or replacing an injector is necessary:

  1. Clean all the connections thoroughly before disconnecting anything.
  3. Disconnect the fuel delivery pipe(s) at the affected injector(s) and plug the open ends to keep out dirt and dust.
  5. Use a 27mm socket and carefully remove the injector from the cylinder head. Remove the heat shield which sits under the injector; it looks like a small, dished washer.

Click image to see an enlarged view

Fig. Fig. 2: Exploded view of diesel fuel injector mounting-observe proper torque values when installing

  1. Remove any soot or dirt from the sealing surfaces.
  3. Install new heat shields for each injector removed. Make sure they are installed with the dished side up. An upside-down heat shield will cause symptoms identical to a failed injector.
  5. Install the new injector(s) and tighten to 50 ft. lbs. (68 Nm). Reconnect the delivery pipes and tighten the connections to 18 ft. lbs. (24 Nm).
  7. Start the engine and check for leaks.

There is no way to test diesel injectors without an elaborate test bench. Your dealer may have this test equipment.

Do not attempt to test the injector by connecting it to its fuel line while out of the engine. You will damage the line by bending it and you run the risk of injury. The injector is under enough pressure that the atomized fuel can penetrate your flesh, inducing blood poisoning.