Experiencing issues with your classic 92 Mercedes Benz 500sl can be frustrating, especially when it involves cold starts and persistent hesitation. This article delves into a real-world scenario faced by a 500SL owner, outlining the troubleshooting process and eventual resolution of these common problems. If you’re grappling with similar symptoms in your vintage Mercedes, understanding this journey may provide valuable insights.
Initial Symptoms: Cold Start Stumble and Hot Soak Hesitation
The owner of this 92 Mercedes Benz 500SL first encountered a recurring problem that manifested in two primary scenarios. Upon a cold start, the engine would crank for a couple of seconds before firing, followed by a noticeable stumble and misfire lasting for 3 to 4 seconds. However, once warmed up and idling at 900rpm, the engine seemed to run smoothly.
The second, and perhaps more perplexing issue, arose after driving, particularly in warmer temperatures (80+ degrees Fahrenheit). After a 20-30 minute drive, followed by a brief 10-15 minute hot soak period, restarting the 92 Mercedes Benz 500SL would trigger a different set of symptoms. This time, a short stumble misfire would be followed by a prolonged hesitation and misfire lasting 10-20 seconds before the engine would run normally again. In more extreme cases, after longer drives and extended hot soak times, the hesitation could persist for a minute or two, even returning intermittently after seeming to resolve itself.
Diagnostic Steps and Suspected Components
Driven to frustration by these inconsistent performance issues, the 92 Mercedes Benz 500SL owner embarked on a diagnostic journey, drawing upon community knowledge and expert advice. Initial suspicions and potential culprits included:
- Over Voltage Protection Relay (OVP): While a quick check revealed a good fuse, the OVP relay itself was found dangling, unmounted. This raised concerns about potential damage to the relay.
- Crank Position Sensor: A common cause of starting and running issues, the crank position sensor was considered a likely suspect.
- Fuel Accumulator: Fuel delivery problems, particularly hesitation after hot soak, often point towards issues with the fuel accumulator.
- Engine Temperature Sensor: Incorrect temperature readings can lead to improper fuel mixtures and starting problems.
Initial Mechanic’s Intervention and Parts Replacement
Seeking professional help, the 92 Mercedes Benz 500SL owner entrusted their vehicle to a trusted independent mechanic. In an effort to pinpoint the problem, a significant number of components were replaced, including:
- Spark plugs (8)
- Distributor caps and rotors (both)
- Spark plug wires
- Ignition coils (both)
- Fuel injectors (all 8)
Despite these extensive replacements, the underlying problem persisted. Frustratingly, the mechanic, unable to isolate the root cause, recommended seeking assistance from a Mercedes-Benz specialist. Notably, the mechanic, demonstrating integrity, did not charge for the extensive diagnostic time or the replaced parts, returning the car to its original state.
Transition to a Mercedes-Benz Specialist and Fuel System Focus
Undeterred, the 92 Mercedes Benz 500SL owner opted to take their car to a different independent mechanic specializing in Mercedes-Benz vehicles. Describing the symptoms – cold start rumble, occasional misfires at idle, hesitation upon acceleration, and a fluctuating oil pressure gauge – the specialist began their diagnosis.
After a week of thorough testing, the specialist concluded that the fuel distributor was the most probable cause. Upon replacement, the immediate results were positive: smooth idle, no misfires, and no initial hesitation. However, a test drive revealed that while the car was running better, it seemed slightly less responsive than before. Crucially, after a brief heat soak, the hesitation issue returned.
Further investigation led to the fuel accumulator being considered again. Replacing it with a used spare initially worsened the problem. Reverting to the original fuel accumulator yielded no improvement.
Final Resolution: Fuel Distributor, Filter, and Mixture Adjustment
After additional days of work, the Mercedes specialist arrived at a final solution. In addition to the previously replaced fuel distributor, they also replaced the fuel filter and meticulously adjusted the air/fuel ratio. This combination of adjustments proved to be the key.
Following these final steps, the 92 Mercedes Benz 500SL exhibited significantly improved performance. While a brief cold start rumble of 2-3 seconds remained, the idle was stable, hesitation was eliminated, and performance felt strong. Even though the oil pressure gauge still showed a slight drop when hot, the primary issues of cold start stumble and hot soak hesitation were resolved.
Conclusion: The Value of Specialization in Mercedes-Benz Repair
This troubleshooting journey highlights the complexities of diagnosing issues in classic vehicles like the 92 Mercedes Benz 500SL. While general mechanics can address many problems, specialized knowledge of Mercedes-Benz systems, particularly fuel injection systems in older models, can be crucial for efficient and accurate diagnosis. In this case, persistence and the expertise of a Mercedes-Benz specialist ultimately led to the successful resolution of persistent cold start and hesitation issues, restoring the enjoyable driving experience of this iconic vehicle.
