3208 TRUCK ENGINE Caterpillar

Low Power


Recommended Procedure


See the chart, Misfiring and Running Rough.


See the chart, Problem With Vehicle or Vehicle Operation.


1. Governor Linkage - Disconnect the governor linkage at the lever on the governor. Move the governor lever by hand until the linkage inside the governor is against the high idle stop. With the accelerator pedal all the way down, adjust the linkage so that the inside linkage is against the high idle stop. Some trucks are equipped with a governor lever of the break over type. On these engines, adjust the governor linkage .250 in. (6.35 mm) longer than necessary for the inside linkage to be against the high idle stop, this will keep tension on the spring at all times.

NOTE: For trucks with tilt cabs, do not make this check with the cab tilted.

2. Governor High Idle Adjustment - If the governor linkage moves the governor lever to the fully open position, check the high idle rpm with a good tachometer. If the high idle rpm is too low, turn the high idle adjustment screw until high idle rpm is correct. See the RACK SETTING INFORMATION for the correct high idle rpm. If high idle rpm can not be made correct with the high idle adjustment screw, there is a problem inside the governor. Disassemble the governor and check for damage to parts or the wrong parts installed in the governor.


3. Inlet Restriction - Air inlet restriction will cause low power and too much smoke when under load. Check for a restriction with a water manometer or a vacuum gauge (which measures in inches of water). Connect the gauge to the engine air inlet between the air cleaner and the engine. With gauge installed, run engine at full load rpm and check the restriction. Maximum restriction of the air inlet is 25 inches (635 mm) of water. If the indication is higher than the maximum permissible restriction, remove dirt from the filter element or install a new filter element and check the restriction again. If the indication is still too high, there must be a restriction in the inlet piping.

4. Exhaust Restriction - Make a visual inspection of the exhaust system and look for damage to piping or for a bad muffler. If no damage is found, you can check the system by checking the back pressure from the exhaust (pressure difference measurement between exhaust outlet and atmosphere). The back pressure must not be more than 34 in. (864 mm) of water. You can also check the system by removing the exhaust pipes from the exhaust manifolds. With the exhaust pipes removed, start and load the engine on a chassis dynamometer to see if the problem is corrected.


5. Water in Fuel - Remove a small amount of fuel from the tank and check for water in the fuel. If there is water in the fuel, remove fuel from tank until it is free of water. Install a new fuel filter and fill the fuel tank with clean fuel. "Prime" (remove the air and/or low quality fuel from the fuel system) the fuel system as per the OPERATION GUIDE (SEBU5216) until all water is out of the fuel system.

6. Fuel With Low Specific Gravity - Remove a small amount of fuel from the tank and measure the API gravity with a fuel hydrometer. The 1P7408 Thermo-Hydrometer can also be used. Special Instruction (GMG00977) gives the test procedure for the 1P7408 Thermo-Hydrometer. Caterpillar engines are rated on fuel having 35 API gravity at 60° F (16° C). If the API gravity of the fuel used is more than 38, the result will be a reduction in power.


7. Low Fuel Pressure - To check the fuel pressure, remove the plug that is just behind the fuel shut-off solenoid on the top cover of the fuel pump housing. Install the necessary fittings and a gauge to check the fuel pressure. Fuel pressure at FULL LOAD rpm must be 30 ± 5 psi (205 ± 35 kPa).

8. Fuel Setting Is Not Correct - Check and make necessary adjustments as per the Testing and Adjusting section of this Service Manual. See the RACK SETTING INFORMATION for the correct fuel setting.

9. Constant Bleed Valve - If the constant bleed valve does not open, the temperature of the fuel in the fuel injection pump housing will increase and the turning action of the fuel injection pump camshaft will cause the fuel to have air in it. To check the constant bleed valve, remove the fuel return line and see if there is a flow of fuel from the constant bleed valve. The flow must be a minimum of 1 pint (0.47 litres) in one minute at full load speed.

10. Shut-off Solenoid or Shut-off Linkage - Remove the solenoid. Start the engine and see if it has full power. If the engine has full power with the solenoid removed, the problem is in the solenoid or in the shut-off linkage. Check for free travel of the linkage. If linkage has free travel make replacement of the solenoid.

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