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The problems in this section are problems that do come about and are normally called "low power". These problems are not necessarily more common than engine problems, but they are possible problems which you need to read and check before an engine is disassembled.Read all of the items but make sure the first three are checked completely before making any engine test. Possible Causes/Corrections Tachometer ErrorTo check, connect a tachometer of known accuracy to the engine. Run the engine and make a comparison of the readings of the vehicle and test tachometers. If vehicle tachometer is defective, make repairs as necessary or install a new tachometer. Engine Operated At High AltitudeLess oxygen at higher altitudes causes the engine horsepower to go down. There is no effect on the horsepower of the engine for the first 2280 m (7500 ft) above sea level of operation. Brakes Do Not Completely ReleaseCheck the brakes by feeling all the brake drums. If the brakes of a wheel do not completely release, the brake drum for that wheel will be hotter than the brake drums for the other wheels. With the truck lifted with a jack, the wheels must have free rotation when turned by hand. Extra Engine Driven EquipmentAir compressors, hydraulic pumps, alternator, and other engine driven equipment that has damage, or that was not installed correctly, or that is not in correct adjustment, can take more horsepower to drive than expected. If necessary, disconnect the equipment and test the engine. Speedometer ErrorA defective speedometer does not give the correct speed or the correct indication of fuel consumption. An indication of low speed can cause the operator to feel that he has a power problem. Speeds Too HighThe need for more horsepower is easy to see as the speed of the vehicle is increased. This is especially true if the front of the vehicle has a large surface area. Application personnel can give you the horsepower necessary for different vehicle designs at different speeds. Overload On VehicleApplication personnel can give you the horsepower needs for different vehicles. High Moving ResistanceSoft ground conditions cause a need for more horsepower. To see if the problem is the engine, test the vehicle on a surface known to be good, or test on a chassis dynamometer. High Wind ResistanceThe horsepower needs for a truck can be divided into two parts. Part of the horsepower is used to move the vehicle and part is used to get through the resistance of the wind. The horsepower necessary to get through the resistance of the wind will increase as the vehicle is used at higher speeds. Vehicles with a large front area have a higher wind resistance and take more horsepower than those with a small front area. Some types of trucks, for example those used for the transportation of automobiles and or boats have high wind resistance even if the front area is small. Moving against the wind has the same effect on wind resistance as does higher