FUEL INJECTORS SERVICE MANUAL NUMBER 22
Page 5C-6 90-860074--1 FEBRUARY 2002
Description
In the EDI fuel injection system, the injectors (with their nozzles in the particular nozzle
holders) are an important connection between the electronically controlled injection pump
and the engine.
The injectors job includes the following:
• Meter the injected fuel.
• Manage and prepare the fuel spray in the cylinder.
• Set the rate of fuel discharge.
• Close-off the injection system from the combustion process taking place inside each
cylinder.
The EDI diesel engines use a hole type injector nozzle and holder. In contrast to the previous
throttling pintle nozzles, the hole type nozzle must be installed in a given position. The spray
holes are at different angles in the nozzle body and must be correctly aligned with regard
to the combustion chamber. The nozzle has a specially shaped end, or nozzle cone, into
which the needle of the injector seats. Two precisely sized and matched pressure springs
hold the needle seated.
The springs are calibrated to allow the needle to unseat at about 27,000 kPa (3,915 psi).
The shape of the needle, the holes and spring pressures restricts the amount of fuel injected
when the needle first starts to open. Not until the needle is completely open is the full amount
of fuel injected. Because it promotes a gradual pressure rise, this action gives soft
combustion and therefore a smooth operating engine.
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