Ignition System:
* Ignition Coil: A weak or failing ignition coil might not provide sufficient spark at higher RPMs (above quarter throttle). This is a common culprit for issues that worsen under load. Testing the coil's output is crucial.
* Ignition Wires/Distributor Cap and Rotor (if applicable): Cracked or worn ignition wires can cause misfires, especially under load. Similarly, a worn distributor cap and rotor (if your 318 has a distributor) can lead to poor spark distribution. Inspect for cracks, arcing, and corrosion.
* Distributor (if applicable): If the problem is intermittent, the distributor's mechanical advance mechanism could be sticking or failing. This would affect spark timing at higher engine speeds.
* Ignition Module (Electronic Ignition Control Unit): This component controls the ignition timing and could be failing, particularly if it's an electronic ignition system.
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the position of the crankshaft. A faulty CKP sensor will cause the engine to stumble or die.
Electrical Connections:
* Loose or Corroded Connections: Check all electrical connections related to the ignition system, fuel system, and engine sensors. Look for corrosion, loose terminals, and broken wires. Pay particular attention to grounds.
* Wiring Harness: A damaged or frayed wire in the main engine harness could be intermittently interrupting the signal to crucial components.
Other Possibilities (Even though you suspect electrical):
* Carburetor (if applicable): If your 318 has a carburetor, it might be having trouble supplying enough fuel at higher throttle openings. Check for clogs, vacuum leaks, or incorrect float levels. (Less likely if you are getting fuel to the pump)
* Fuel Filter: Even with a good fuel pump, a clogged fuel filter can restrict fuel flow under load.
* Exhaust Restriction: A severely clogged catalytic converter or exhaust system can create backpressure and cause the engine to lose power.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all wiring, connections, and components in the ignition system. Look for any obvious damage.
2. Check for Spark: Use an inline spark tester to verify that the spark plugs are receiving a strong spark at higher RPMs.
3. Check Fuel Pressure: Even though you checked the pump, double-check fuel pressure at various throttle positions using a fuel pressure gauge. It might be dropping under load.
4. Test the Ignition Coil: A professional test is best, but some basic tests can be done. Look for cracks or obvious damage.
5. Check Engine Codes: If your Dodge has an OBD system (check the year), scan for any diagnostic trouble codes (DTCs). These codes can pinpoint the problem.
If you're not comfortable performing these checks yourself, taking it to a qualified mechanic is recommended to avoid further damage. Explain the issue and the steps you've already taken – this will save them time and potentially money.
