CLIP 5P9297 - Caterpillar

Measurement Of Inlet Manifold Air Pressure
The efficiency of an engine can be checked by making a comparison of the pressure in the inlet manifold with the information in the Technical Marketing Information (TMI).This test is used when there is a decrease of horsepower from the engine, yet there is no actual sign of a problem with the engine.The correct pressure for the inlet manifold is also given in the Technical Marketing Information (TMI), "Fuel Setting and Related Information". These standards are established under the following conditions:
barometric pressure of 96 kPa (29 Inches Hg)
outside air temperature of 29°C (85°F)
API rated fuel of 35Any change from these conditions can change the pressure in the inlet manifold. The outside air may have a higher temperature and a lower barometric pressure than the values that are given above. This will cause a lower inlet manifold pressure measurement than the pressure in the TMI. Outside air that has both a lower temperature and a higher barometric pressure will cause a higher inlet manifold pressure measurement.A difference in fuel density will change horsepower (stall speed) and boost. If the fuel is rated above 35 API, the pressure in the inlet manifold can be less than the pressure that appears in the TMI. If the fuel is rated below 35 API, the pressure in the inlet manifold can be more than the pressure that appears in the TMI.Note: Be sure that the air inlet or the exhaust does not have a restriction when you are checking the inlet manifold air pressure.Use 1U-5470 Engine Pressure Group to check the pressure in the inlet manifold.Remove the plug on the aftercooler housing in order to measure inlet manifold pressure.
Illustration 1 g00293196
1U-5470 Engine Pressure Group This tool group has a gauge to read pressure in the inlet manifold. Refer to Special Instruction, SEHS8524 for the operation of this tool group.