Fuel Control Pressure Regulator

Created: 7/6/00

Last updated: 

Author/source: Dave Sontos  dsontos(AT)sybercom.net

Description: There is a tiny hole in the stainless-steel diaphragm that separates the lower chambers from the upper chambers of the fuel distributor. This hole allows fuel to flow from the lower chambers into an area above the control plunger. The Control Pressure Regulator controls the pressure in this area, limiting the degree to which the control plunger can be lifted for a given amount of airflow into the engine. Limiting the movement of the control plunger in turn limits the richness of the air-fuel ratio. The Control Pressure Regulator achieves this control by bleeding off fuel pressure from the control plunger and returning fuel back to the fuel tank.


Symptoms exhibited by the car included multiple cold starts before the engine would idle and then the idle would be rough. Acceleration would make the engine cough and sputter and die until several minutes till the engine warmed.


Attach fuel pressure gauge between fuel distributor center line and the Control Pressure Regulator (CPR) with the shut off valve between the CPR and the gauge. Attach a fused jumper wire between terminals 87 and 30 of the RPM Relay connector to energize the fuel pump and pressurize the fuel system. The cold engine fuel pressure should read around 35-40 psi. Next rotate the gauge valve to the closed position. By doing so the CPR will be isolated, thus the pressure gauge will show system pressure. System pressure should be around 65 psi. If the readings do not change when operating the gauge valve your CPR is not working.


If your car may have been sitting for a while it is a good possibility that debris in the fuel line has plugged up the CPR inlet side. Inside the inlet to the CPR is a very fine screen. Dirt from a contaminated system will plug up this screen making the CPR inoperable. Remove both fuel lines from the top of the CPR and using a shop air hose blow air into the outlet side fuel port of the CPR. Make sure you wear some sort of eye protection when you do this. The air should dislodge the dirt in the inlet side of the CPR. Shine a light into the inlet and inspect for dirt. You may need to use a small probe to dislodge any remaining dirt here and clear with shop air. You should now be able to see the screen at the bottom of the inlet hole. Place the ends of both fuel lines from the CPR into a one pound coffee can or other suitable container and run the fuel pump for a couple of minutes to flush out any remaining dirt from the fuel line. Re-attach the fuel lines to the CPR and repeat the Diagnosis again to confirm normal operation and check for leaks in the fuel system.

The CPR assembly may be completely disassembled for cleaning. When I removed mine and opened the two halves I found the inside completely filled with some insect infestation. Although I donít believe this affected its operation it looked like hell. Inside the CPR is the heater and electrical contacts and also the vacuum bellows. Check the electrical with a VOM and the vacuum bellows with a hand vacuum pump.

Original reference: http://www.vabch.com/dsontos/regulato.htm

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