The efficiency of an engine can be checked by making a comparison of the pressure in the inlet manifold with the information given in the Technical Marketing Information (TMI). 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.
The correct pressure for the inlet manifold is listed in the TMI. Development of this information is performed under the following conditions:
- 96 kPa (28.8 in Hg) dry barometric pressure
- 25 °C (77 °F) outside air temperature
- 35 API rated fuel
Any 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 pressure.
Note: The Caterpillar Electronic Technician (ET) may be used to check the pressure in the inlet manifold.
| Tools Needed | ||
|---|---|---|
| Part Number | Part Description | Qty |
| 1U-5470 or 198-4240 |
Engine Pressure Group or Digital Pressure Indicator Gp |
1 |
|
|
Illustration 1 g00293196
1U-5470 Engine Pressure Group
Refer to Special Instruction, SEHS8907, “Using the 1U-5470 Engine Pressure Group ” for the instructions that are needed to use the 1U-5470 Engine Pressure Group . Refer to Operation Manual, NEHS0818, “Using the 198-4240 Digital Pressure Indicator Gp ” for the instructions that are needed to use the 198-4240 Digital Pressure Indicator Gp
Illustration 2 g01134338
Pressure test location
(1) Plug
Use the following procedure in order to measure the inlet manifold pressure:
- Remove plug (1) from the air inlet cover.
- Connect the 1U-5470 Engine Pressure Group to the air inlet cover at the pressure test location.Note: A tee fitting or some other plumbing component will be necessary to allow the boost pressure sensor to be connected with a test location.
- Record the value.
- Compare the value that was recorded in Step 3 to the pressure that is given in the TMI.