Porsche 911 Testing Bosch CIS

		Four pressure tests can be made with this tester:  Cold Control Pressure - engine cold, valve open Warm Control Pressure - engine warm, valve open Primary Pressure - engine cold or warm, valve closed (closed valve eliminates control pressure) Rest Pressure - engine warm, valve open The CIS pressures shown in this book are for the warm control pressures. For pressures for tests A & C, consult the vehicle service manual, a Mitchell Fuel Injection manual, of Robert Bosch Service Guide booklet for Fuel Injection. To make tests: For test "A" (above), the engine should be cold, standing several hours or overnight.   Relieve fuel system pressure.   Make sure fuel filter is not clogged. Replace if doubtful.   Clean dirt off the fuel distributor cap.   Referring to the typical CIS hookup diagram, hook up the tester between the fuel distributor and the control pressure regulator. The hose without the flow control valve should be connected to the center of the fuel distributor. The hose with the valve should be connected to the hose removed from the fuel distributor or connected directly to the control pressure regulator.   CAUTION: hand tighten any adapters with the O-rings to avoid damage to O-rings.   In a few cases, to get the right combination of threads to connect, the adapters may have to be piggy-backed.   Reactivate fuel pump, start the engine and check for leaks.   When the tester is connected, remove the air from the system   If your tester has a release valve under the gauge, wrap a rag over the valve and depress button until the air is released. Do not do this over a hot engine or manifold.   If your tester has a bleed-off valve, put the end of the bleed-off valve tubing in a fuel container and with fuel pump operating, bleed until air is removed.   If your tester has none of the above, position the gauge downward as far as the hoses will allow with the gauge below the hoses and control valve. Operate fuel pump with the engine off. Open and close the control valve at least 5 times with the valve in the off and on position at least 12 seconds.   When pressure stabilizes, read the gauge. If the Cold Control Pressure is not correct, the warm-up regulator may be at fault.   If pressure is okay, run the pressure checks   Warm Control Pressure and Rest Pressure must be measured with engine warm. Primary Pressure can be measured with engine cold or warm.   Pressure range   If pressures are not within the normal range on the control Pressure Warm test, try adjusting the fuel pressure regulator. If it cannot be adjusted to normal pressures, replace it unless the problem is as below (b)   If the pressure is low with engine running and at idle, check to see if the voltage is at least 11.5V at the warm-up regulator plug contacts. If full voltage is available at the plug, then the warm-up regulator may need replacing.   If the pressure is too low, test the fuel pump volume. Also, there may be a blockage in the supply line or leakage in the return line. If the system has none of these, the fuel system pressure needs adjustment. Consult the factory manual or fuel injection manual for the procedure.   If Rest Pressure drops too quickly, check for leaks at O-rings and fuel line connections. If no external leaks, check for a leaking cold start valve of fuel injectors. If still no leaks there, leakage may be at the fuel pump check valve or at the O-ring on the relief valve in the fuel distributor. Repair or replace.   If no problems can be found in the fuel injection system through pressure testing, fuel pump should be checked. For this, your tester should have a bleed-off valve and tubing. If you do not have one, it can be purchased from your tool supplier. With gauge hooked up to pressure test, put bleed-off tube into a fuel container of at least 2 quarts or 2 liters. Fuel flow in 30 seconds should be 1.5 - 2.0 pints or 3/4 - 1 liter. Turbo cars may have a volume of 20-25% more than non-turbo.   Deactivate fuel pump and relieve fuel system pressure. With key off, put bleed-off tubing in a fuel can and press bleed-off valve. If your tester has no bleed-off valve assembly, wrap rags around connection and release slowly. A bleed-off assembly can be purchased from your tool supplier.   Remove tester and reconnect all lines.   Start engine and check for leaks.   Remove fuel from all hoses. If fuel remains in gauge hose assembly, connect the smallest banjo bolt adapter into the quick coupler over a fuel container. Hold gauge above hose and fuel will flow into the fuel can.   [click to enlarge]

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Clean dirt off distributor cap

Wayne R. Dempsey, Co-Founder & DIY Expert