brake control, can be placed into position 1, 2, or 3. In position 1 the compression brake is activated only on two cylinders; position 2 will activate the compression brake on four cylinders; position 3 will allow all six cylinders to provide compression braking.

On the right-hand side of the control panel are two warning lights - one yellow, the other one red. The yellow light is labeled warning, while the red light is labeled stop. When the yellow light comes on during engine operation, this indicates that a Celect system problem has been detected and recorded in the ECM memory. The problem is not serious enough to shut down the engine, but should be checked out at the earliest opportunity. If the red light comes on, the operator should immediately bring the vehicle to a stop and shut off the engine.

Celect System Operation

The ECI (electronically controlled injection) Celect system uses an engine-driven gear pump to pull fuel from the fuel tank. The fuel is passed through a primary filter or filter/water separator unit, then to the ECM where the fuel is circulated through a cooling plate. The cooling plate, mounted to the rear of-the ECM, ensures adequate cooling of the electronic package.

The gear pump is designed to deliver fuel to the fuel manifold at 140 psi, which supplies the electronically controlled injectors. A spring-loaded bypass valve allows excess fuel under pressure to return to the suction side of the pump to maintain maximum system pressure.

A rocker arm and pushrod assembly mechanically operates the injector. The injector requires rocker arm actuation of the plunger to create high fuel pressure for injection. To control both the start of injection timing and the quantity of fuel metered, the ECM sends out a pulse-width-modulated (PWM) electrical signal to each injector. The PWM signal determines the start of injection, while the duration of this signal determines how long the injector can effectively continue to spray fuel into the combustion chamber, as the plunger is forced down by the rocker arm assembly. A shorter PWM signal means that the effective stroke of the injector plunger will be decreased. A longer PWM signal means that the effective stroke will be increased. The start of injection and the duration of the PWM signal is determined by the ECM, based on the various input sensor signals and the preprogrammed PROM information within the ECM. Each PROM is designed for a specific engine/vehicle combination, based on the desired horsepower setting and rpm, the tire size, and gear ratios used in the vehicle.

Contained within the injector are a timing plunger, a return spring, and an injector control valve - that is the key to the operation. The control valve is electrically operated, receiving signals from the ECM to energize/de-energize, which determines the start of injection. The length of time that this solenoid is energized determines the quantity of metered fuel to be injected into the combustion chamber. Also within the injector body is a metering spill port which must be closed to allow injection, a metering piston, the bias spring, and the spill-timing port. The injection sequence of events occur as follows:

1. The injector receives a signal from the ECM; the injector control valve will close and the metering phase begins while the metering piston and timing plunger are bottomed in the injector.

2. As the camshaft rotates, the injector pushrod cam follower will ride down the cam ramp, thereby allowing the rocker arm and pushrod to be forced up by the energy of the timing plunger return spring. Fuel at gear pump pressure of 140 psi can flow into the fuel supply passage and unseat the lower check valve, allowing the metering chamber to be charged with pressurized fuel as long as the timing plunger is being pulled upward by the force of the large external spring. Fuel pressure, acting on the bottom of the metering piston, forces it to maintain contact with the timing plunger within the bore of the injector body.

3. Metering ends when the ECM energizes the injector control valve, causing it to open. Pressurized fuel can flow through the open injector control valve into the upper timing chamber, which stops the upward travel of the metering piston. To ensure that the metering piston remains stationary, the small bias spring in the timing chambers holds it in place, while the timing plunger continues upward due to camshaft rotation. Fuel and spring pressure, acting on the metering piston, will ensure fuel pressure is maintained below the piston to keep the lower metering ball-check valve closed. This allows a precisely metered quantity of fuel to be trapped in the metering chamber.

4. As long as the timing plunger moves upward due to the rotating camshaft lobe action and the