Fuel System:
* Fuel Pump: A weak fuel pump might struggle to keep up with the increased fuel demand at higher speeds. The pump might be failing or the fuel filter might be clogged, restricting fuel flow.
* Fuel Filter: A clogged fuel filter is a common cause of sputtering and poor performance, especially under load.
* Fuel Pressure Regulator: This regulates fuel pressure within the system. A faulty regulator can lead to inconsistent fuel delivery.
* Fuel Injectors: Clogged or failing fuel injectors can deliver insufficient fuel, causing sputtering. This is more likely to be a problem at higher RPMs under load.
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides inaccurate readings to the engine computer, leading to improper fuel mixture. This can manifest as sputtering, especially under acceleration.
Ignition System:
* Spark Plugs & Wires: Worn spark plugs or damaged ignition wires can cause misfires, resulting in sputtering, particularly at higher speeds where the engine is working harder.
* Ignition Coil: A failing ignition coil might not provide sufficient spark to all cylinders consistently, leading to misfires and sputtering. This is also more likely under load.
* Distributor (if equipped): Older vehicles like some 1999 Expeditions might still use a distributor. Worn components within the distributor can cause similar issues. (Less likely, but possible)
Other Potential Issues:
* Catalytic Converter: A clogged catalytic converter can restrict exhaust flow, causing back pressure and affecting engine performance. This often manifests as sputtering and a loss of power.
* Oxygen Sensor: A faulty oxygen sensor provides inaccurate readings to the engine computer, impacting fuel mixture and potentially causing sputtering.
* Transmission Issues: While less likely to cause *sputtering*, transmission problems could indirectly lead to similar symptoms if the engine is struggling to maintain speed due to slipping or other issues. This is usually accompanied by other transmission symptoms like slipping, hard shifting, etc.
* Vacuum Leaks: A vacuum leak can disrupt the proper air/fuel mixture, causing erratic performance.
Troubleshooting Steps:
1. Check the easy stuff first: Start by inspecting the spark plugs and wires. If they look worn or damaged, replace them. Also check the fuel filter – it's inexpensive and easy to replace.
2. Check engine codes: Use an OBD-II scanner to retrieve any diagnostic trouble codes (DTCs) stored by the engine computer. These codes can point directly to the problem.
3. Fuel pressure test: A mechanic can perform a fuel pressure test to determine if the fuel pump and regulator are delivering the correct pressure.
4. Professional Diagnosis: If the simple checks don't reveal the problem, taking your Expedition to a qualified mechanic for diagnosis is essential. They have the tools and expertise to diagnose more complex issues.
Important Note: Don't continue driving the vehicle excessively while it's sputtering. This could cause further damage to the engine or catalytic converter.
