Usage:
3406, 3408, 3412 Engines In All Applications
Many low power complaints for the above engines are the result of problems in the fuel ratio control group. The four major areas to check are the diaphragm, seals, housing and valves.
Diaphragm And Gaskets
The diaphragm must be tested for air leaks caused by distortion during assembly or by small holes. To do this, connect a 70 kPa (10 psi) air source and a pressure gauge to the boost tap on the fuel ratio control housing. The air source must have a regulator and shut-off valve. Charge the fuel ratio control to 70 kPa (10 psi) and shut off the air valve.
Watch the gauge for an indication of an air leak. While the control is charged, put some water and soap solution around the covers to check for air leakage between the gasket and covers. If there is leakage, install a new diaphragm or gasket as necessary.
Teflon Seal And O-Ring
The limiter valve assembly has an O-ring seal behind the Teflon seal on the piston. It is possible for the O-ring seal to swell (increase in size) when it is hot and cause the Teflon seal to stick in the housing. The Teflon seal will not stick at room temperature. To check the seals, heat the housing and valve in oil to 82°C to 93°C (180°F to 200°F). If the limiter valve assembly moves freely, the O-ring did not swell and the Teflon seal did not stick.
Machined Bore In Housing
Check the housing for a rough, machined bore. The bore must be shiny in comparison to the casting surface, and it must feel smooth against a finger nail.
On engines which have 161000 km (100,000 miles) check the bore for visible wear. The worn bore permits side movement of the limiter valve assembly.
If the bore is rough or worn, install a new housing.
Limiter Valve Assembly
The limiter valve, used in the limiter valve assembly, has four oil holes with an oil groove under the holes. Burrs on the oil groove will not let the internal valve, which fits into the limiter valve assembly, move freely. If the internal valve does not move freely, the driver must shift to lower gears during operation on a hill.
To correct this problem, use a round file, emery cloth and lapping compound to remove the burrs. Be careful to remove only the burrs. Also, do not remove any material from the internal valve.
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This must be done very carefully to prevent damage to the bore of the limiter valve.
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Areas to check when troubleshooting fuel ratio control groups.