Experiencing a no-start issue with a classic 1987 Mercedes 560 Sec can be frustrating for any car enthusiast. Recently, we encountered this exact problem and embarked on a systematic diagnosis focusing on the fuel system. This article outlines the steps taken to troubleshoot the issue, offering insights that may be helpful if you are facing similar challenges with your own 560 SEC.
The initial step involved checking the fuel pump relay. Bypassing the relay is a common diagnostic technique to isolate potential relay failure. In this case, bypassing the relay yielded no change, indicating the issue likely resided elsewhere in the fuel system.
Next, attention turned to the fuel filter. A clogged or contaminated fuel filter is a frequent culprit in fuel delivery problems. Upon replacement, the condition of the old fuel filter was revealing. The fuel within was found to be watery, sludgy, and clearly degraded, suggesting a long period of neglect or contamination within the fuel system. Replacing the fuel filter, along with the copper washers on the banjo fittings, is crucial for maintaining proper fuel flow and pressure.
Suspecting contaminated fuel as a significant contributor, the next step was to drain the old fuel. By disconnecting the main fuel line from the pump, a substantial amount of old fuel was drained. Initially, the drained fuel appeared heavily contaminated, but continued draining revealed progressively cleaner fuel. This process highlighted the importance of fresh, clean fuel for optimal engine operation and ruled out heavily contaminated fuel as the sole immediate cause, although long-term issues related to fuel system contamination remained a possibility.
Focus then shifted to the fuel distributor. Following expert guidance, the fuel distributor was removed for inspection. A critical component within the distributor is a central pin, which, upon inspection, was found to be sticky, sludged up, and exhibiting signs of rust. This pin’s proper function is essential for fuel distribution, and its condition directly impacts engine performance. Cleaning the pin with brake/clutch cleaner and a brass brush, followed by lubrication with a light oil and compressed air cleaning, aimed to restore its free movement. During this process, a loose or stretched main O-ring at the base of the fuel distributor unit was also noted, indicating a potential source of leaks or pressure issues. Despite cleaning and refitting the fuel distributor, no immediate improvement in the starting condition was observed.
Currently, the 1987 Mercedes 560 SEC still cranks and attempts to start, with a marginal improvement possibly attributable to the new fuel filter. An intriguing observation is the intermittent gurgling or bubbling sound emanating from the fuel pumps, suggesting potential air in the system or pump cavitation.
Next steps to further diagnose this no-start condition include addressing the identified issues and exploring related components:
- Fuel Distributor O-Ring: Identifying the correct part number and replacing the loose O-ring in the fuel distributor is essential to eliminate potential fuel pressure leaks and ensure proper sealing.
- Fuel Pump Replacement: Given the age of the vehicle and the observed noises, replacing at least one fuel pump is a prudent step to ensure reliable fuel delivery.
- Fuel Valve Inspection: Investigating the fuel valve located near the pump/filter assembly, although its exact name is currently unknown, is warranted to rule out any blockage or malfunction in this part of the fuel system.
Further observations include a constant buzzing from the fuel pumps when directly powered and a persistent loud hum from the rear left of the car, possibly indicating another electrical or mechanical issue requiring investigation.
While progress has been made in isolating potential issues within the fuel system of this 1987 Mercedes 560 SEC, the no-start condition persists. Continued methodical troubleshooting, addressing each identified component, will be key to restoring this classic Mercedes to its optimal running condition. Stay tuned for further updates as the diagnosis progresses.
