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Why your 1986 BMW 318i Turns over but engine run?

It sounds like you're having a frustrating issue with your 1986 BMW 318i! Here's a breakdown of common reasons why a car turns over but doesn't start, and how to troubleshoot them:

1. Fuel Delivery Problems:

* Empty Fuel Tank: The most basic issue! Check your fuel gauge.

* Fuel Pump Failure: The fuel pump moves fuel from the tank to the engine. It can fail, making a buzzing sound when you turn the key.

* Clogged Fuel Filter: The filter prevents debris from reaching the engine. A clogged filter restricts fuel flow.

* Fuel Line Issues: Cracked or disconnected fuel lines can prevent fuel from reaching the engine.

2. Spark Problems:

* Spark Plugs: Worn or fouled spark plugs can prevent a spark.

* Spark Plug Wires: Cracked or loose wires can interrupt the spark.

* Ignition Coil: The coil delivers the high-voltage spark to the plugs. If it fails, you won't have ignition.

* Distributor Cap and Rotor: In older cars like yours, these components can wear out and prevent proper spark distribution.

3. Air Intake Problems:

* Air Filter: A clogged air filter restricts airflow to the engine.

* Intake Manifold Leak: A leak in the intake manifold can draw in unfiltered air, disrupting the air-fuel mixture.

4. Engine Compression:

* Blown Head Gasket: A head gasket failure can cause compression loss, preventing the engine from starting.

* Worn Piston Rings: Rings can wear down, allowing combustion gases to escape, leading to compression loss.

5. Other Potential Issues:

* Battery: A weak or dead battery can prevent the starter motor from turning the engine over.

* Starter Motor: The starter motor itself can fail, preventing the engine from turning.

* Timing Belt: A broken or improperly timed timing belt can cause catastrophic damage.

Troubleshooting Steps:

1. Check for Spark: Remove a spark plug wire, ground it to the engine block, and crank the engine. Look for a spark.

2. Check for Fuel: Remove a fuel line at the injector and crank the engine. Look for fuel flow.

3. Inspect Air Filter: Remove and inspect the air filter.

4. Listen for Fuel Pump: Turn the key to "on" (not start) and listen for a buzzing sound from the fuel pump.

5. Check Battery: Use a voltmeter to check the battery voltage.

Important Note: Diagnosing a no-start condition can be tricky. If you're not comfortable working on your car, it's best to take it to a qualified mechanic.

Let me know if you have any more questions or need further advice.