1981/02/04 Caterpillar

Inspection And Test Procedures To Follow When Fuel Ratio Control Does Not Operate Correctly


3400 Series Engines

Some customers have had problems with engine performance because the fuel ratio control did not operate correctly. When the fuel ratio control causes a performance problem, use the procedure that follows to inspect and test the control.

Location of points to check in fuel ratio control.

1. The internal (inside) valves (3) and (6) must operate freely. If they do not, carefully inspect the valves for burrs (very small edges of turned-up metal), especially at locations (7) through (11). Any burrs must be removed.


Crocus cloth can be used to remove burrs, but the corners (9), (10), and (11) on the valve spool must not be made round.

2. Check for leakage of boost pressure. Connect a controlled air supply with a shut-off valve to the boost port (opening) and put 70 kPa (10 psi) of air pressure in the control, then close the valve. If the control does not hold the pressure, find the leakage: A) Check the gasket at (1). B) Check the surface (12) of the 2P8226 Cover to be sure it is flat. C) Inspect diaphragm (2) for damage or wrong assembly.

3. Inspect the surface (5) of the bore in the 2P8225 Housing (4) to be sure it is smooth and even. A rough bore will not permit a good seal or smooth operation.

4. Inspect the 2P8225 Housing (4) for cracks or porous (has very small holes) metal which can permit leakage.

Inspection of fuel ratio control parts.

Caterpillar Information System:

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1981/03/06 Changes Have Been Made To Caterpillar Service Literature
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