This article mainly introduces caterpillar 3208 Diesel Truck Engine Low Power Troubleshooting
1. Preparation of vehicle for wheel horsepower test
(consult dynamometer manufacturer's operating instructions for specific details on correct operation)
NOTE: Always perform the Primary Engine Test procedure before vehicle is installed on chassis dynamometer.
Calculate the allowable limits that the customer can expect from his engine and present these tigures to him.
Caterpillar engines are rated with the conditions that follow.
Barometric pressure =747 mm (29.4 in) of mercury Inlet air temperature =29℃(85F) at air cleaner inlet Fuel gravity =API gravity of 35 at 16℃(60F)
Measure and record these variables.
a. Place vehicle on the chassis dynamometer. Tie thevehicle in a way that will not add any load to the drive wheels. Do not pull wheels down into dynamometer drive rolis.
Check the radiator coolant level, crankcase oil level, tire pressure, tire condition, remove rocks frorm the tire tread and connect exhaust system.
NOTICE Recapped tires should be run on a chassis dynamo-
meter only at the customer's own risk.
b. Operate vehicle at 60% of rated speed with moderate load until oil and coolant temperatures reach their normal range for operation.
NOTICE If there is a heavy vibration, drive shaft whip, tire bounce, etc., do not continue with dynamometer test until cause of the problem is corrected. Engines that have had new internal parts installed should be operat-
ed on a run-in schedule before operation at full load.
For run-in schedule information, make reference to General Instructions section of this Service Manual.
2.Put transmission in direct gear and the difterential in the highest speed ratio.Operate vehicle at Q maximum engine speed and increase chassis dynamometer load until a speed of 50 rpm less than rated speed is reached（continuity light should be每
on）.Maintain this speed for one minute and record the engine speed and wheel horsepower.
NOTE:If horsepower is low and poor maintenance issuspected，remove air cleaner and check horsepower again to see if a plugged air cieaner could be the problem.
3a.If the wheel horsepower is correct，find the sel point（balance point）of the engine（speed at which theload stop pin just touches the torque spring or stop bar）.At this point the continuity light should flicker（go off and on dimly）.
f the set point（balance point）is correct，then the lowpower complaint cannot be validated.No further test or repairs are necessary.
If the set point（balance point）is low，see Procedure No.4.
3b.If the wheel horsepower is below the correct value.
find the set point（balance point）of the engine（speed at which the load stop pin just touches the torque spring or stop bar）.At this point the continuity light should flicker（go off and on dimly）.
f the set point（balance point）is corect，see Procedure No.5.
If the set point（balance point）is low，see Procedure No.4.
4. Ifthe set point(balance point) is low, the high idle will have to be increased to raise the set point
(balance point) to the correct rpm(the point at which the continuity light just comes on).
NOTE: If the set point (balance point) is still low and high idle has been adjusted to maximum, disengage clutch while maximum throttle position is maintained.
Now observe high idle rpm and, if lower than previously adjusted, check frame-to-engine-mount.A damaged or loose engine mount may put the linkage in a bind and prevent maximum governor position at load conditions.
5. If the set point (balance point) was correct and the wheel horsepower was low, install the 1U5470
Engine Pressure Group and do the wheel horsepower test again as shown in Procedure No 2.
At ful load rpm, measure the boost and the fuel pressure. See Fuel Setting and Related Information Fiche to find the correct boost pressure for a particular engine(since the engine is in vehicle, be sure to make reference to the General Notes in the Fuel Setting and Related Information Fiche to determine the correct boost pressure with air cleaner and muffier installed). If boost is low, check connections ahead of turbine side of turbocharger for exhaust leaks and connections after compressor side of turbocharger for inlet air leaks.
Measurement Of Pressure In Inlet
Manifold
The efficiency of an engine can be checked by making a comparison of the pressure in the iniet manifold with the information given in the Fuel Setting And Related Information Fiche. This test is used when there is adecrease of horsepower from the engine, yet there is no real sign of a problem with the engine.
The correct pressure for the inlet manifoid is given in the Fuel Setting And Related Information Fiche.
Development of this information is done with these conditions: a.747 mm(29.4 in) of mercury barometric pressure.
b.229℃(85F) outside air temperature.
C.35API rated fuel.
Any change fom these conditions can change the pressure in the inlet manifold. Outside air that has higher temperature and lower barometric pressure thangiven above will cause a lower horsepower and a lowerinlet manifold pressure measurement than given in the Fuel Setting And Related Information Fiche. Outside air that has a lower temperature and a higher barometric pressure will cause higher horsepower and a higher inlet manitold pressure measurement.
A difference in fuel rating will also change horsepower and the pressure in the inlet manifold. If the fuel israted above 35 AP1, pressure in the inlet manifold can be less than given in the Fuel Setting And Related Information Fiche. If the fuel is rated below 35 APl, the pressure in the iniet manifold can be more than given in the Fuel Setting And Related Information Fiche, Be Sure That The Air Iniet And Exhaust Do Not Have A Restriction When Making A check Of Pressure In The Inlet Manifold.
Use the 1U5470 Engine Pressure Group to check the pressure in the inlet manifold.
This group has a gauge to read pressure in the inlet manifold. Special instruction, Form No. SEHS8907 is with the tool group and gives information for its use.
Low Power Troubleshooting
1. Preparation of vehicle for wheel horsepower test
(consult dynamometer manufacturer's operating instructions for specific details on correct operation)
NOTE: Always perform the Primary Engine Test procedure before vehicle is installed on chassis dynamometer.
Calculate the allowable limits that the customer can expect from his engine and present these tigures to him.
Caterpillar engines are rated with the conditions that follow.
Barometric pressure =747 mm (29.4 in) of mercury Inlet air temperature =29℃(85F) at air cleaner inlet Fuel gravity =API gravity of 35 at 16℃(60F)
Measure and record these variables.
a. Place vehicle on the chassis dynamometer. Tie thevehicle in a way that will not add any load to the drive wheels. Do not pull wheels down into dynamometer drive rolis.
Check the radiator coolant level, crankcase oil level, tire pressure, tire condition, remove rocks frorm the tire tread and connect exhaust system.
NOTICE Recapped tires should be run on a chassis dynamo-
meter only at the customer's own risk.
b. Operate vehicle at 60% of rated speed with moderate load until oil and coolant temperatures reach their normal range for operation.
NOTICE If there is a heavy vibration, drive shaft whip, tire bounce, etc., do not continue with dynamometer test until cause of the problem is corrected. Engines that have had new internal parts installed should be operat-
ed on a run-in schedule before operation at full load.
For run-in schedule information, make reference to General Instructions section of this Service Manual.
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2.Put transmission in direct gear and the difterential in the highest speed ratio.Operate vehicle at Q maximum engine speed and increase chassis dynamometer load until a speed of 50 rpm less than rated speed is reached（continuity light should be每
on）.Maintain this speed for one minute and record the engine speed and wheel horsepower.
NOTE:If horsepower is low and poor maintenance issuspected，remove air cleaner and check horsepower again to see if a plugged air cieaner could be the problem.
3a.If the wheel horsepower is correct，find the sel point（balance point）of the engine（speed at which theload stop pin just touches the torque spring or stop bar）.At this point the continuity light should flicker（go off and on dimly）.
f the set point（balance point）is correct，then the lowpower complaint cannot be validated.No further test or repairs are necessary.
If the set point（balance point）is low，see Procedure No.4.
3b.If the wheel horsepower is below the correct value.
find the set point（balance point）of the engine（speed at which the load stop pin just touches the torque spring or stop bar）.At this point the continuity light should flicker（go off and on dimly）.
f the set point（balance point）is corect，see Procedure No.5.
If the set point（balance point）is low，see Procedure No.4.
4. Ifthe set point(balance point) is low, the high idle will have to be increased to raise the set point
(balance point) to the correct rpm(the point at which the continuity light just comes on).
NOTE: If the set point (balance point) is still low and high idle has been adjusted to maximum, disengage clutch while maximum throttle position is maintained.
Now observe high idle rpm and, if lower than previously adjusted, check frame-to-engine-mount.A damaged or loose engine mount may put the linkage in a bind and prevent maximum governor position at load conditions.
5. If the set point (balance point) was correct and the wheel horsepower was low, install the 1U5470
Engine Pressure Group and do the wheel horsepower test again as shown in Procedure No 2.
At ful load rpm, measure the boost and the fuel pressure. See Fuel Setting and Related Information Fiche to find the correct boost pressure for a particular engine(since the engine is in vehicle, be sure to make reference to the General Notes in the Fuel Setting and Related Information Fiche to determine the correct boost pressure with air cleaner and muffier installed). If boost is low, check connections ahead of turbine side of turbocharger for exhaust leaks and connections after compressor side of turbocharger for inlet air leaks.
7. The fuel transfer pump pressure(measured at plug on top of fuel pump housing) must not be less than140kPa(20 psi) at full load conditions. Normal fuel pressure at full load rpm is 205±35kPa(30±5
psi). If fuel pressure is low or erratic, check for the conditions that follow in the order shown: A. Air in the Fuel System... Disconnect the fuel return line at the tank. Place this end of the line in a container of fuel to see if air bubbles are presentwith the engine running. If air bubbles are observed check for loose connections or other line leaks ahead of fuel transfer pump.
B. Restrictions... Check for a plugged fuel filter or crimped(damaged) fuel lines.
C. Too Much Fuel Returned to Tank.. Block the tuel return line to stop all fuel returned to tank. Check fuel pressure again, and, if a significant pressure increase is observed, an incorrect constant bleed orifice may be the problem. Install the correct orifice.
Do not run the engine under load for more than 5
minutes with return line blocked.
D. Damaged Fuel Transfer Pump Parts... Check bypass valve to see it dirt or other debris could make the valve stick, Clean or replace valve if damaged. If bypass valve is good, remove and disassemble fuel transfer pump to check for wear in the gears.
8.A very smal amount of air in the fuel may not affect the transfer pump fuel pressure, but could affect the performance at the nozzles. The 2P8278 Flow Tube can be installed ahead of the tuel transfer pump.
This will allow a visual check of any air in the fuel when the engine is running. Another method to check for air in the fuel is to put the fuel tank end of the fuel return line in a container of fuel.
9. Install the 6V7925 Fuel Rate Indicator according to Special Instruction, Form No. SEHS8346. The specified fuel rate at ful load is given in the Fuel Setting And Related Information Fiche.
Do the wheel horsepower test again as shown in Procedure No.2, but this time
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record the fuel rate and rpm.
NOTE: This fuel system has a constant flow of fuel that is returned to the fuel tank. This orifice must be blocked before accurate fuel rate readings can be taken. Do not run the engine under load for more than
5 minutes with return line blocked.
10. If the fuel rate was too low, install 5P4203 Field Service Tool Group and check the fuel system setting. The correct fuel system setting is given in Fuel Setting And Related Information Fiche. If fuel system setting is not correct, the adjustment procedure is shown in the Testing and Adjusting section of this Service Manual under the subject Fuel System Setting.
If the fuel rate was low, and the fuel system setting is correct, check the items that follow in the sequence shown: A. Remove nozzles and check to see if they are the correct nozzles for your engine or if they have been wire brushed. Either condition will affect performance.
B. Check for any restrictions to tuel flow in lines between fuel filter and nozzies. Any sharp bend in the lines could cause a restriction of fuel delivery.
C. Check governor for worn parts.A worn bushing or worn spring seat can change governor operation.
Also check to see if the correct governor spring is installed.
D. Check fuel injection pumps for wear and for the correct calibration. Put the fuel injection pump group on the fuel injection test bench. Perform a fuel delivery test to determine if the correct amount of fuel is delivered by each pump.
11. Use the 8T5300 Diesel Timing Indicator Group to check the timing of the fuel injection pump camshaft to the engine camshaft. See Fuel System of the Testing and Adjusting section of this Service Manual for the subject Checking Engine TimingAnd Automatic Timing Advance Unit With 8T5300
Timing Indicator Group.
12. Use the 8T5300 Timing Indicator Group to check the automatic timing advance unit. Check to see that the advance is smooth and that the amount ofadvance is correct. See Fuel System of the Testing and Adjusting section of this Service Manual for the subject Checking Engine Timing And Automatic Timing Advance Unit With 8T5300
Timing Indicator Group.
If rpm, timing, and fuel rate are found to be within specifications, the engine should produce acceptable power(unless engine has excessive internal friction, ie, high crankcase oil level). When all the above conditions are within specifications, and the wheel horsepower is still lower than expected, some component of thevehicle must be absoroing too much power. Do not continue with engine troubleshooting, but locate and correct the problem with the vehicle.(Caterpilar is not responsible for problems with vehicle).
13. Measure the boost again as detailed in Procedure No.5. If rpm, timing, fuel rate and boost are found to be within specifications, the engine should produce acceptable power(unless engine has excessive internal friction,i.e., high crankcase oil level). When all the above conditions are within specifications, and the wheel horsepower is still lower than expected, some component of the vehicle must be absorbing too much power. Do not continue with engine troubleshooting, but locate and correct the problem with the vehicle.
(Caterpillar is not responsible for problems with vehicle).
14. If boost is still low, check inlet manifold temperature. If temperature is too high, check the aftercooler for possible restrictions to the coolant.
This condition reduces the amount of air in cylinder for combustion (since warmer air is less dense). If manifold temperature is correct, check the turbocharger for mechanical problems (ie, wrong nozzles, worn bearings).
