Fuel Delivery Issues:
* Fuel Pump: Even if the truck runs at idle, the fuel pump may not be delivering enough fuel under load (acceleration). A weak pump might struggle to keep up with the increased demand. Listen closely near the fuel tank for a humming sound when the key is turned on; a weak or failing pump might make a faint or irregular sound.
* Fuel Filter: A clogged fuel filter restricts fuel flow, especially under higher demands. This is a relatively cheap and easy part to replace, so it's worth checking even if it's been changed recently.
* Fuel Pressure Regulator: This regulates the fuel pressure in the system. A faulty regulator can cause low pressure, leading to poor acceleration. A pressure gauge test is needed to diagnose this accurately.
* Clogged Fuel Injectors: These injectors spray fuel into the cylinders. If they're clogged or dirty, they won't deliver enough fuel for acceleration. Cleaning or replacing them is a possible solution.
Ignition System Issues:
* Ignition Coil: A weak or failing ignition coil might not provide enough spark under load.
* Worn Distributor Cap and Rotor (if applicable): These components distribute the high voltage to the spark plugs. Cracks or wear can lead to misfires under load. (Less likely on a 1996, as many 5.9s were already using coil-on-plug, but worth checking if you have a distributor).
* Spark Plugs and Wires: Worn spark plugs or damaged wires can cause misfires, especially under stress.
Transmission Issues (Automatic):
* Torque Converter: A problem with the torque converter in an automatic transmission can prevent power transfer during acceleration. This is less likely if the engine revs freely without moving the truck.
* Transmission Solenoids or Valve Body: Internal problems within the transmission itself can restrict power transfer.
Other Possibilities:
* Throttle Position Sensor (TPS): Although you've replaced sensors, ensure the TPS is correctly calibrated. An incorrectly calibrated TPS can cause poor acceleration.
* Mass Airflow Sensor (MAF): Even if replaced, a faulty MAF sensor can still cause problems. Try disconnecting it (the engine will run in a "limp home" mode) to see if performance improves. *Note:* Disconnecting it is only for diagnostic purposes; do not drive long distances with it disconnected.
* Computer Issues (PCM/ECM): A failing PCM/ECM (Powertrain Control Module/Engine Control Module) is a less likely but possible culprit. This requires more advanced diagnostics.
Troubleshooting Steps:
1. Check the basics: Fuel level, battery voltage, and all fuses and relays.
2. Listen for unusual noises: Pay attention to any sounds from the fuel pump, engine, or transmission during acceleration attempts.
3. Check fuel pressure: Use a fuel pressure gauge to measure fuel pressure at idle and during attempted acceleration. This is crucial for diagnosing fuel delivery issues.
4. Inspect spark plugs and wires: Check for fouling, cracks, or damage.
5. Obtain diagnostic codes: Use an OBD-II scanner to read any trouble codes stored in the PCM. This can provide valuable clues.
6. Consider professional help: If you've exhausted these steps, taking it to a qualified mechanic specializing in older Dodge trucks is advisable. They have the tools and experience to diagnose more complex problems.
Remember to always prioritize safety when working on your vehicle. If you're not comfortable performing these checks yourself, seek professional help.
