COVER-VALVE 3447562 - Caterpillar

3406C (4CK1-Up) Electronic EnginesLow power complaints may result when the output of the 9X7793 Rack Sensor is non-linear at the higher fuel system rack values. This problem cannot be diagnosed using the ECAP (part number 8T8697 with NEXG4522 Dual Truck Service Program Module) alone.
Symptoms of this problem are significant losses in wheel horsepower on a chassis dyno accompanied by equally low readings of fuel rate and boost. This failure mode usually shows up as a 40 to 60 wheel horsepower loss at rated conditions.
To determine whether a problem exists, use the rack dial indicator group and ECAP together to validate the rack sensor linearity. Install the mechanical dial indicator on the fuel system and then move the rack manually to the point that the rack reads 1.00 mm on the ECAP. Adjust the dial indicator to read 1.00 mm. Then move the rack manually 1.00 mm at a time on the dial indicator and record the ECAP reading. The two numbers should follow within 0.25 mm up to 15.00 mm of rack.
Graph 1.Graph 1 reflects a linear (straight line) output generated by a rack sensor functioning properly. Two types of non-linearity have been identified to date. Graph 2 shows a slight non-linearity at the end of the rack travel, but would probably not cause the engine to have excessively low power. The second example of non-linearity is shown in Graph 3. This type of output would result in the low power, fuel rate and boost levels mentioned previously. Replacement of the rack sensor may be necessary to restore the engine to its normal power levels if the rack values obtained simulate those shown in Graphs 2 and 3.
Graph 2.
Graph 3.