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(Diagnosis With Chassis Dynamometer)
1. Preparation of vehicle for fuel consumption test (consult dynamometer manufacturer's operating instructions for specific details on correct operation). Always perform the Primary Engine Test procedure before vehicle is installed on chassis dynamometer.a. Place vehicle on the chassis dynamometer. Tie the vehicle in a way that will not add any load to the drive wheels. Do not pull wheels down into dynamometer drive rolls.Check the radiator coolant level, crankcase oil level, tire pressure, tire condition, remove rocks from the tire tread and connect exhaust system.
Recapped tires should be run on a chassis dynamometer only at the customer's own risk.
b. The maximum acceptable fuel rate must be calculated for the customer's engine by use of the formula that follows: Find the rated brake specific fuel consumption (lb-bhp/hr) from the Fuel Setting And Related Information Fiche and add 0.25 mm (.010 in) manufacturing tolerance. Multiply this value by the advertised engine horsepower (plus 3% manufactures tolerance) and divide by the density of the fuel (lbs/gal).c. Calculate the allowable limitt that the customer can expect from his engine and present these figures to him. Caterpillar engines are rated with the conditions that follow: Barometric pressure = 747 mm (29.4 in) of mercuryInlet air temperature = 29°C (85°F) at air cleaner inletFuel gravity = API gravity of 35 at 16°C (60°F)Measure and record these variables.2. Operate vehicle at 60% of rated speed with moderate load until oil and coolant temperatures reach their normal range for operation.
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 operated on a run-in schedule before operation at full load.
Put transmission in direct gear and the differential in the highest speed ratio. Operate vehicle at maximum engine speed and increase chassis dynamometer load until a speed of 50 rpm less than rated speed is reached (continuity light should be on). Maintain this speed for one minute and record the engine speed, wheel horsepower and fuel rate.3. If the fuel rate and the wheel horsepower are both acceptable, then the engine is not the cause of the complaint, or the complaint is not valid. Refer to section Problem With Vehicle Or Vehicle Operation.4. If the wheel horsepower is low, regardless of how the fuel rate measures, refer to the Low Power Troubleshooting Chart. The low power problem must be corrected first.5. If the fuel rate and wheel horsepower are both too high, check 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).If the set point (balance point) is high, the high idle will have to be decreased to lower the set point (balance point) to the correct rpm (point at which the continuity light just comes on). If the set point (balance