* Weak or failing battery/alternator: If the battery is weak or the alternator isn't charging properly, the sudden demand for power when engaging the drivetrain can deplete the available power, causing the engine to stall. Test the battery voltage and the alternator's output while the engine is running. A load test on the battery is also recommended.
* Transmission problems: Issues within the transmission itself can put excessive strain on the engine. This could include:
* Low transmission fluid: Check the transmission fluid level and condition. Low fluid or severely contaminated fluid can cause problems.
* Internal transmission damage: Worn clutch packs, damaged gears, or other internal issues can create excessive drag, causing the engine to stall. This requires a professional diagnosis.
* Torque converter issues: A faulty torque converter can slip excessively, placing undue stress on the engine.
* Engine problems: While less likely to be the *sole* cause, engine problems can contribute. These include:
* Carburetion issues (if applicable): If it's a carbureted engine, a clogged fuel filter, dirty carburetor, or faulty choke could be causing insufficient fuel delivery under load.
* Ignition problems: Weak spark, faulty distributor cap or rotor, or problems with the ignition coil can lead to misfires, particularly under load, resulting in stalling.
* Vacuum leaks: A vacuum leak can disrupt the engine's air/fuel mixture, leading to poor performance and stalling.
* Drive-shaft or other drivetrain issues: A binding drive shaft, differential problems, or other drivetrain components could create excessive resistance, making it difficult for the engine to turn over.
Troubleshooting Steps:
1. Check the basics: Start with the easiest things first: battery voltage, alternator output, and transmission fluid level.
2. Listen carefully: When the engine dies, pay close attention to any unusual noises (grinding, whining, etc.) from the transmission or drivetrain.
3. Professional diagnosis: Given the complexity, taking the van to a mechanic familiar with older vehicles is highly recommended. They have the tools and expertise to properly diagnose the problem.
Without more information (engine type, any warning lights, etc.), it's impossible to pinpoint the exact cause. The above points offer a range of possibilities, and a thorough inspection is necessary to determine the root of the issue.
