High-Probability Issues:
* Fuel System Problems: This is the most common cause.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to hard starting and stalling. This is a cheap and easy check. Replace it as preventative maintenance even if it doesn't seem clogged.
* Fuel Pump: A failing fuel pump may not deliver enough fuel pressure, causing the engine to starve for fuel, especially under load (when driving). Listen for the pump whirring when you turn the ignition key – it should be audible for a few seconds.
* Fuel Injectors: Clogged or faulty injectors can prevent proper fuel delivery. This requires specialized diagnostic tools and likely professional attention. Symptoms include rough running, poor fuel economy, and hard starting.
* Low Fuel Level: Sounds obvious, but sometimes overlooked.
* Water in the Fuel: Water in the fuel system can cause similar symptoms. This can be particularly problematic in older diesels.
* Electrical System Issues:
* Crankshaft Position Sensor (CKP): This sensor tells the ECU the engine's rotational position. A faulty CKP will prevent the engine from starting or cause it to cut out.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP disrupts the ignition timing, leading to starting problems and stalling.
* Battery/Alternator: A weak battery can prevent starting. A failing alternator won't recharge the battery, leading to intermittent problems.
* Wiring Harness: Corrosion or damage to the wiring harness can cause intermittent electrical faults.
* Engine Management System:
* ECU (Engine Control Unit): A faulty ECU can cause a wide range of problems, including hard starting and stalling. This is less likely but possible, and diagnosis requires specialized tools.
Less Likely, but Possible Issues:
* Glow Plugs (if equipped): Important for cold starting in diesel engines. Faulty glow plugs can make starting difficult, especially in cold weather.
* Mass Airflow Sensor (MAF): Though less common on older diesels, a faulty MAF sensor can cause erratic running and stalling.
* Vacuum Leaks: A vacuum leak in the intake system can disrupt the engine's operation.
Troubleshooting Steps:
1. Check the Obvious: Fuel level, battery voltage, and any obvious signs of damage.
2. Replace the Fuel Filter: This is the cheapest and easiest first step.
3. Listen for the Fuel Pump: Check if it's running when the ignition is turned on.
4. Obtain Diagnostic Codes: Use an OBD-II scanner (specifically one that works with older diesels, many are not compatible) to retrieve any diagnostic trouble codes (DTCs). This can significantly narrow down the possibilities. A dedicated Volvo diagnostic tool may be needed for a more precise diagnosis.
5. Professional Diagnosis: If you can't identify the problem after these steps, it's best to take the vehicle to a qualified mechanic, especially one familiar with older diesel Volvos. They have the diagnostic tools and expertise needed to diagnose and repair more complex issues.
Without more specific symptoms (e.g., does it crank but not start? Does it cut out suddenly or gradually? Does it happen only under load?), it's difficult to pinpoint the exact cause. The information above should give you a good starting point for investigation. Remember safety first – always work on the vehicle in a well-ventilated area.
