Under the Hood – August 2007

Fuel Pressure Sensor Diagnostic Codes
A new flash file has been released for use on Caterpillar C9 engines (Serial No. 9DG1-Up.) The new software is equipped for a fuel pressure sensor. You may generate a code when you flash the software into an engine that is not equipped with a fuel pressure sensor.

The following procedure disables the fuel pressure sensor in the engine control module(ECM): Establish communications between the Caterpillar Electronic Technician (ET) and the ECM and go to the ECM configuration screen. Select “Engine Monitoring Parameters.” Select “Fuel Pressure Sensor” and change the value to “Not Installed.” Once the parameter for the fuel pressure sensor has been turned off, clear the codes from the ECM by cycling the key switch to the OFF position for 30 seconds. Next turn it to the ON position. Use Cat ET in order to clear the codes for the fuel pressure sensor.

Thrust Angle Adjustment
The Mack MaxLite 20/40 EZ suspension was implemented into production on CXN and CHN model chassis.It incorporates an easy method of adjusting drive axle thrust angle; a method that is more precise and eliminates the need for shims and spacers. (See Figure 1.)
Drive axle thrust angle adjustment requires a thrust angle adjustment tool (Tool No. 6000-85107240).

This tool is a hex-shaped bar that is inserted through the two hex holes located in the eccentrics on the left-side spring hanger brackets.

The thrust angle is adjusted easily by loosening the pinch bolts and then using a 16mm socket and 1/2-inch breaker bar to rotate the tool in the desired direction.

V-Band Clamp
Mack has implemented a heavy-duty V-band clamp for the air inlet elbow connection at the inlet manifold on ASET AI and AMI engines to replace the used worm screw-type clamp (Part No. 180GB329M).

The revised clamp is a T-bolt-type clamp that uses a quick latch feature. (See Figure 2.) When you install this clamp, apply a thin film of engine oil around the inside diameter of the clamp and tighten the T-bolt nut to 70 +/-5 lb.-in.

Replacing Lifters For Unit Injectors
For Caterpillar 3126E, 3126B, C-10, C-12 and C-13 truck engines, the company recommends replacing the injector and the corresponding lifter assembly after a hard injector seizure. (See Figure 3.)

A hard injector seizure happens when the injector plunger fails on the down stroke. As the plunger seizes, separation occurs in the mechanism and the pushrod cup for the fuel injector disengages from the insert for the rocker arm. This crushes the pushrod between the rocker arm and the lifter assembly, which damages the roller follower’s pin. This damage may not be visible.

If the cylinder head is removed, you need to examine the positions of the arrows on the lifter rollers’ axles on all six unit injector lifter assemblies. If an arrow is more than 10 degrees from vertical, replace the lifter assembly. The incorrect position of the arrow indicates that the roller’s axle has begun to turn in the lifter body and the oil that is gathering on top of the axle is not positioned correctly, resulting in the roller’s axle not being lubricated properly.

If the axle has turned into the lifter body, the roller eventually may separate from the lifter body, which can damage the cylinder block.