3116 and 3126 Truck Engines Measurement Of Pressure In Inlet Manifold

The efficiency of an engine can be checked by making a comparison of the pressure in the inlet manifold with the specifications given in the TIM (Technical Marketing Information). This test is used when there is a decrease of horsepower from the engine, yet there is no real sign of a problem with the engine. Development of this information is done with these conditions:

* 737 mm (29 in) of mercury barometric pressure (dry).
* 29°C (85°F) outside air temperature.
* 35 PI rated fuel.

Any change from these conditions can change the pressure in the inlet manifold. Outside air that has higher temperature and lower barometric pressure than given above will cause a lower horsepower and a lower inlet manifold pressure measurement than given in the TMI. Outside air that has a lower temperature and a higher barometric pressure will cause higher horsepower and a higher inlet manifold pressure measurement.

A difference in fuel API rating will also change horsepower and the pressure in the inlet manifold. If the fuel is rated above 35 API, pressure in the inlet manifold can be less than given in TMI. If the fuel is rated below 35 API, the pressure in the inlet manifold can be more than given in TMI. Fuel API rating can be easily checked using the 1P7408 Thermo-Hydrometer. Instructions are given in Special instruction SEHS8874. BE SURE THAT THE AIR INLET OR EXHAUST DOES NOT HAVE A RESTRICTION WHEN MAKING A CHECK OF PRESSURE IN THE INLET MANIFOLD.

1U5470 Engine Pressure Group

Pressure Test Location
(1) Plug.

To check the inlet manifold pressure, remove one of the plugs (1) on top of inlet manifold. Connect the adapter, seal, reducing bushing, and 1U5470 Engine Pressure Group to this opening.

The 1U5470 Engine Pressure Group has a gauge to read pressure in the inlet manifold. Special Instruction, SEHS8524, is with the tool group and gives instruction for its use.

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