* Fuel Pump: This is the top suspect. A weak fuel pump might struggle to maintain sufficient pressure at consistent highway speeds (steady, moderate fuel demand), but it can still push enough fuel under hard acceleration (high fuel demand). The increased engine speed helps the pump work more effectively. A failing pump often makes a whining noise when it's struggling.
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing similar symptoms. This is a cheaper and easier fix than a fuel pump replacement, so it's always worth checking first.
* Pick-up Tube in Fuel Tank (or debris in the tank): The pick-up tube inside the fuel tank draws fuel to the pump. If it's clogged, damaged, or the tank has debris that restricts flow, you'll see reduced fuel delivery under moderate demand.
* Fuel Pressure Regulator: This component regulates the fuel pressure in the system. A malfunctioning regulator might not provide enough pressure at highway speeds.
* Throttle Position Sensor (TPS): A faulty TPS can send incorrect signals to the engine computer, resulting in poor fuel delivery at certain throttle positions. This is less likely but still possible.
* Mass Airflow Sensor (MAF): If the MAF sensor is malfunctioning, the engine computer might not get an accurate reading of the air intake, leading to poor fuel management. Again, less likely than the fuel system issues.
Troubleshooting Steps:
1. Check the Fuel Filter: This is the easiest and cheapest first step. Replace it if it's dirty or damaged.
2. Check Fuel Pressure: You'll need a fuel pressure gauge to measure the fuel pressure at the fuel rail. This will tell you if the pump is delivering sufficient pressure. Compare your reading to the factory specifications for your Dakota's engine.
3. Listen for Fuel Pump Noise: Listen carefully near the fuel tank while the engine is running. A whining or struggling sound indicates a failing fuel pump.
4. Inspect the Fuel Tank and Pick-up Tube (more involved): This might require dropping the fuel tank to inspect the pick-up tube for clogs or damage. Be aware of fire hazards when working with fuel.
It's highly recommended you take your 1991 Dodge Dakota to a qualified mechanic if you're not comfortable performing these checks yourself. A proper diagnosis is crucial to ensure the correct repair is made. Ignoring the problem could lead to engine damage.
