* Fuel Pump: A weak fuel pump can't keep up with the demand for fuel when you accelerate. The engine gets enough fuel at idle, but when you need more, it starves. This is a very common cause of this symptom.
* Fuel Filter: A clogged fuel filter will restrict fuel flow, causing similar symptoms to a weak fuel pump. It's a cheap and easy part to replace, so it's usually checked first.
* Ignition System: Problems with the ignition coil, distributor cap, rotor, or spark plug wires can cause misfires, leading to sputtering and stalling under load. A failing ignition coil is common in older vehicles and often exhibits this behavior.
* Throttle Position Sensor (TPS): This sensor tells the computer how much the throttle is open. A faulty TPS can send incorrect signals, leading to erratic fuel delivery.
* Mass Air Flow Sensor (MAF): If equipped, a dirty or faulty MAF sensor provides inaccurate air flow readings, causing the computer to deliver the wrong amount of fuel.
* Carburetor (if applicable): If your Bronco II has a carburetor instead of fuel injection, the problem could be related to carburetor issues like a clogged jet, a stuck float, or a faulty accelerator pump.
* Vacuum Leaks: A vacuum leak in the intake system can disrupt the air/fuel mixture, leading to rough running and stalling.
Troubleshooting Steps:
1. Check the fuel filter: This is the easiest and cheapest thing to check first. Replace it if it's dirty or damaged.
2. Listen for the fuel pump: When you turn the key to the "on" position (before cranking), you should hear the fuel pump briefly run. If you don't hear it, the pump might be faulty.
3. Check the spark: Have someone crank the engine while you check for spark at the spark plug wires using a spark tester. Weak or no spark indicates a problem in the ignition system.
4. Inspect the distributor cap and rotor: Look for cracks, corrosion, or worn contacts. Replace if necessary.
5. Inspect spark plug wires: Look for cracks, fraying, or loose connections. Replace if needed.
6. Check for vacuum leaks: Visually inspect all vacuum lines and connections for cracks or loose fittings.
Important Note: Since the problem occurs under load (when you accelerate), it strongly suggests a fuel delivery issue. Focus on the fuel pump and filter first. If you're not comfortable working on your vehicle, take it to a qualified mechanic. They have the tools and experience to diagnose the problem accurately and safely.
