Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Mercedes Benz 560SECFACTORY OEM SERVICE PROCEDURE
Residual Pressure & Internal Leak Testing
- Run engine and check fuel pressures as previously described. Turn engine off and check residual pressure. Pressure should slowly drop below 41 psi (2.9 kg/cm2 ). This is the pressure required to open fuel injectors. If pressure drops rapidly to zero psi, inspect check valve on fuel pump or check for a bad injector.
- If pressure drops slowly to zero psi, disconnect fuel return line at diaphragm pressure regulator. There should be no flow of fuel, although slight seepage is acceptable. Plug return line IMMEDIATELY if fuel flows heavily.
- Pinch by-pass line-to-fuel inlet hose at fuel accumulator. If pressure holds with line pinched, replace fuel accumulator. If no leaks are found, remove cold start valve from manifold and check for leaks under pressure. Replace valve if necessary.
- Disconnect pressure gauge and clean any spilled fuel. Reconnect all fuel lines and run engine. Visually check all connections and lines for leaks.
Factory Service Tools
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.