When improper calibration (balance) of fuel injector pumps or injectors occurs, there is a dif-ference in the amount of fuel injected into each of the cylinders. If some pumps or injectors deliver more fuel per stroke than others, the engine will be UNBALANCED; that is, some cylinders will carry a greater load than others. This condition may be detected by differences in cylinder exhaust temperatures and firing pressures, and by smoky exhaust from the overloaded cylinders. Roughness in operation and engine vibration are also indicators of an unbalanced condition.

It is important to remember that many other types of engine difficulties may cause engine symptoms identical with those due to unbalance. So when unbalance is suspected, consider first a few of the other faults that may be present such as poor condition of piston rings, inaccurate exhaust pyrometers and thermocouples, mistimed or faulty engine exhaust or inlet valves.

Improper Timing

Improper timing of a fuel system will result in uneven operation or vibration of the engine. Early timing may cause the engine to detonate and lose power. Cylinders which are timed early may show low exhaust temperatures. Late timing usually causes overheating, high exhaust temperatures, loss of power, and smoky exhaust. Although, usually, improper fuel injection timing is caused by failure to follow the manufac-turers instructions for timing, there may be other causes for the difficulty, depending upon design of the particular systems. For example, fuel injection time in the injection pump of a Bosch system may get out of time because of a worn pump camshaft. The same problem may occur when the adjusting screw on the injector control rack of a GM system becomes loose. Either of these conditions will change fuel injection timing. Faulty calibration and improper timing are generally due to failure to follow instructions given in the engine technical manual and the fuel injection equipment maintenance manual. These manuals should always be consulted and fol-lowed whenever timing or calibration difficulties arise.