M11 Series – Service Manual – 014-002   Engine Testing (Chassis Dynamometer)

The performance of an engine installed in “on-highway” vehicles can be tested on a chassis dynamometer.

NOTE: Due to driveline inefficiencies and engine-driven accessories, the rated horsepower will be reduced by approximately:

• 20 percent for single-axle vehicles
• 25 percent for tandem-axle vehicles.

The net horsepower available is called wheel horsepower (WHP).

NOTE: These percentages are used for engine run-in only and are not to be used as absolute figures.

The following are general safety precautions to be observed while operating the chassis dynamometer.

• Use tires that have more than 160 km [100 mi] on them. Do not use new tires.
• Do not use recapped tires or tires of different sizes or designs.

• Make sure the tires are inflated to the manufacturer’s specifications.
• Remove all rocks or other material from the tread of all tires that will be rotating on the dynamometer rollers.

• Make sure there is correct overhead clearance for exhaust stacks, air deflectors, or other attachments above the cab.

CAUTION  The “tie-down” chains must have slack to prevent damage to the chassis dynamometer.

• Carefully position the vehicle on the rollers.
• Attach the “tie-down” chains to the rear of the vehicle, and put wheel chocks in front of the front wheels.

• Adjust the vehicle and dynamometer room exhaust system to make sure all exhaust gases are removed from the room.
• Refer to the chassis dynamometer and vehicle manufacturer’s recommendations and specifications for testing procedures.

Check the engine coolant level to be sure it is filled to the proper level.

WARNING  Check the coolant level only when the engine is stopped. Wait until the coolant temperature is below 50°C [120°F] before removing the pressure cap. Failure to do so can cause personal injury from heated coolant spray.

CAUTION  Do not add cold coolant to a hot engine. This can cause engine casting damage. Allow the engine to cool to below 50°C [120°F] before adding coolant.

Check the engine lubricating oil level to be sure it is filled to the proper level.

NOTE: Use a known source of “good” quality No. 2 diesel fuel. This is very important since No. 1 diesel fuels, along with most other alternate fuels, are lighter (lower specific gravity, higher API gravity) than No. 2 diesel fuel. The lighter the fuel, the lower the energy content (BTU) per gallon (liter, etc.).

To properly monitor engine performance, record the following parameters. To limit dynamometer operating time, instrument the engine to make as many checks as possible.

• Engine speed rpm with a verified tachometer
• Fuel pressure
• Fuel rate (Use Service Tool, Part Number 3376375)
• Fuel temperature (if needed to correct fuel rate)
• Fuel inlet restriction
• Fuel drain line restriction
• Intake manifold pressure

• Intake air restriction
• Exhaust air restriction
• Coolant temperature
• Engine blowby
• Lubricating oil pressure
• Coolant pressure
• Inlet manifold air temperature
• Turbocharger inlet air temperature
• Oil temperature

Use digital optical tachometer, Part Number 3377462, to check and verify engine speed.

Measure the fuel pressure. Install the pressure gauge, Part Number ST-435-6, or the pressure gauge in the fuel measuring device, Part Number 3376375, to the fitting on the fuel shutoff valve.

NOTE: Pressure gauge, Part Number ST-435-6, is included with snap rail pressure gauge, Part Number 3375932.

Use fuel measuring device, Part Number 3376375, to measure the rate of fuel consumption. For more information, refer to “Engine Testing – General Information”.

Install the fuel measuring device as follows:

• The fuel return hose from the engine to the fuel measuring device (A).
• The fuel inlet hose to the fuel filter inlet (B).
• The return hose from the device (C) to the fuel tank.
• The fuel inlet hose to the device from the fuel tank suction line (D).

NOTE: Adjust the fuel rate to compensate for temperature variation if required.

Measure the fuel inlet restriction. Install a vacuum gauge, Part Number ST-434, between the fuel filter and the gear pump inlet.

NOTE: Do not measure fuel inlet restriction with the fuel measuring device installed. This will not measure the inlet restriction of the vehicle’s supply plumbing.

Hold the gauge at the same level as the gear pump.

NOTE: The gauge will not measure the correct vacuum if the gauge is not held at the same level as the gear pump.

Operate the engine at maximum horsepower rpm on STC engines.

NOTE: On CELECT™ and CELECT™ Plus, it is not necessary to operate the engine to maximum horsepower, only high idle.

Observe the reading on the gauge.

Correct the restriction or replace the fuel filter.

Use Pressure Gauge, Part Number ST-1273, to measure fuel drain line restriction.

NOTE: Do not measure fuel drain line restriction with the fuel measuring device installed. This will not measure the drain line restriction of the vehicle’s return plumbing.

Hold the gauge at the same level as the connection.

NOTE: The gauge will not measure the correct pressure if the gauge is not held at the same level as the connection.

Operate the engine at maximum horsepower rpm on STC engines.

NOTE: On CELECT™ and CELECT™ Plus, it is not necessary to operate the engine to maximum horsepower, only high idle.

Observe the reading on the gauge.

Measure the intake manifold pressure (turbocharger boost). Install pressure gauge, Part Number ST-1273, in the intake manifold as shown.

Observe the reading on the pressure gauge.

When operating an engine on a chassis dynamometer, follow these steps for best results and safe operation.

For CELECT™ and CELECT™ Plus engines

Lock the cooling fan in the “ON” mode. This can be done by installing a jumper across the temperature switch, or by supplying shop air to the control valve. Refer to the fan drive manufacturer for the recommended procedure.

Monitor the intake manifold air temperature using INSITE™ in the monitor mode, or install Fluke digital thermometer, Part Number 3822666, and thermocouple wire kit, Part Number 3822988, into the intake manifold.

The intake manifold air temperature must not exceed the maximum allowable temperature. The engine protection system will disrupt performance if the temperatures exceeds this level. Maintain intake manifold air temperature at the nominal level or below during chassis dynamometer operation.

If the intake manifold temperature exceeds 77°C [170°F], shut off the engine. Allow the engine to cool.

Inspect the CAC fins for obstructions to the air flow.

Check the fan drive. Make sure the fan is locked in the “ON” mode.

Remove any obstructions such as a winterfront or debris. Manually lock the shutters in the “OPEN” position if equipped.

Inspect the dynamometer room for adequate supply of suitably cool or outside air. Make sure that dynamometer room recirculation is not an issue.

Resume the test.

STC Engines

Lock the cooling fan in the “ON” mode. This can be done by installing a jumper across the temperature switch or by supplying shop air to the control valve. Refer to the fan drive manufacturer for the recommended procedure.

Remove any obstructions to the air flow across the radiator such as a winterfront. Manually lock the shutters in the “OPEN” position, if equipped.

Install a Fluke digital thermometer, Part Number 3822666, and attach thermocouple wire kit, Part Number 3822988, into the intake manifold. Monitor the intake manifold temperature. The temperature must not exceed 77°C [170°F].

If the intake manifold temperature exceeds the above limits, shut off the engine. Allow the engine to cool.

Inspect the radiator fins for obstructions to the air flow. Check the fan drive to make sure it is locked in the “ON” mode.

Resume the test.

Measure the intake pressure drop across the charge air cooler, if applicable.

This test can be done with a mercury manometer or two separate gauges, Part Number ST-1273. If two gauges are being used, calibrate both gauges on a common pressure source to ensure consistency.

Install one pressure gauge, Part Number ST-1273, in the fitting in the turbocharger compressor outlet elbow. Install the other pressure gauge in the fitting in the intake manifold.

When measuring the pressure drop, operate a dynamometer at the rpm that delivers the maximum horsepower of engine tested. Engine speed will be 1600-1700 rpm on most engines.

Measure the inlet air restriction. Install the vacuum gauge, Part Number ST-434, or a manometer in the intake air piping.

NOTE: The gauge adapter must be installed at a 90 degree angle to the air flow in a straight section of pipe at a minimum of one pipe diameter before the turbocharger.

Operate the engine at maximum horsepower rpm and advertised horsepower.

Observe the reading on the gauge or manometer.

Measure the exhaust air restriction. Install the pressure gauge, Part Number ST-1273, or a manometer in the exhaust air piping.

The gauge adapter must be installed near the turbocharger in a straight section of pipe at the turbine outlet.

Operate the engine at maximum horsepower rpm and advertised horsepower.

Observe the gauge or manometer.

Measure the engine crankcase pressure.

Use blowby checking tool, Part Number 3375150, and water manometer, Part Number ST-1111-3.

Install the water manometer to the blowby checking tool. Observe the engine blowby.

Engine blowby must not exceed the following specifications:

Use Pressure Gauge, Part Number 3375275, to measure lubricating oil pressure.

Install the pressure gauge to the main oil rifle and observe the oil pressure.

Use coolant pressure/temperature/flow analyzer kit, Part Number 3822994, to measure engine coolant pressure.