Possible Causes:
* Ignition Coil: The ignition coil is responsible for generating the high voltage spark that ignites the fuel in your engine. A failing coil can cause intermittent misfires or complete engine shutdown. The fact that restarting the car with a jumper wire to the coil suggests a possible issue with the coil itself.
* Ignition Control Module (ICM): The ICM acts as the "brain" for your ignition system, controlling the spark timing and duration. A faulty ICM can cause similar symptoms to a failing coil.
* Spark Plugs/Wires: While less likely to cause a complete shutdown, worn-out spark plugs or corroded wires can lead to misfires that contribute to engine stalling.
* Fuel Pump: A failing fuel pump could be preventing fuel from reaching the engine, leading to a sudden stall. This is less likely if the engine restarts easily.
* Loose or Corroded Connections: Check all connections in your ignition system, including the coil, ICM, and wiring harness.
Troubleshooting Steps:
1. Inspect the Ignition Coil:
* Visually inspect the coil for signs of damage, cracks, or corrosion.
* Use a multimeter to test the resistance of the coil's primary and secondary windings. Check against the specifications in your Volvo service manual.
* If the coil tests faulty, replace it.
2. Check the Ignition Control Module:
* If the coil tests good, suspect the ICM.
* Use a multimeter to test the ICM's input and output signals. Consult your Volvo service manual for specific tests.
* If the ICM is faulty, replace it.
3. Inspect Spark Plugs and Wires:
* Inspect the spark plugs for wear, carbon buildup, or gaps outside the recommended specifications.
* Examine the spark plug wires for cracks, fraying, or loose connections.
* Replace any faulty plugs or wires.
4. Consider Fuel Pump:
* If the car stalls and takes a long time to restart, a failing fuel pump is possible.
* Check fuel pressure using a gauge. A low fuel pressure reading points to a pump issue.
5. Inspect Electrical Connections:
* Thoroughly inspect all electrical connections in the ignition system, including those to the coil, ICM, spark plugs, and wiring harness.
* Clean any corroded terminals and tighten loose connections.
Important Notes:
* Safety First: Always disconnect the battery before working on electrical components.
* Consult Service Manual: The specific procedures and testing values for your 1988 Volvo 740 Turbo wagon are in your service manual.
* Professional Diagnosis: If you're not comfortable with electrical work, consider taking your car to a qualified mechanic for diagnosis and repair.
Additional Tips:
* Check for codes: Your Volvo may have a diagnostic code that provides more clues about the problem.
* Consider the environment: Does the problem occur more often in hot weather or when the engine is cold? This could narrow down the cause.
By systematically working through these steps, you should be able to identify and resolve the issue causing your Volvo 740 Turbo to shut off while driving.
