#4 cylinder misfire changed coil packs & plugs still throws code

1. Check for Fuel System Issues

A faulty or clogged fuel injector on cylinder 4 is a very common cause of a single-cylinder misfire after the ignition system has been addressed.

Swap the Injector: The simplest diagnostic step is to move the fuel injector from cylinder 4 to a known good cylinder. If the misfire code follows the injector to the new cylinder, the injector is bad and needs replacement.

Listen for Operation: You can use a stethoscope or a long screwdriver against the injector body to listen for a clear clicking sound, which indicates it is pulsing. A lack of sound or a dull sound suggests an issue.

Check Wiring: Inspect the electrical connector and wiring harness for the cylinder 4 injector for any corrosion, damage, or loose connections.

2. Check for Air/Vacuum Leaks

As you're planning on replacing the plenum gaskets, this is a likely culprit for a lean misfire, especially one that is noticeable at idle.

Visual Inspection: Look for any cracked or loose vacuum lines around the intake manifold/plenum area.

Carb Spray Test: With the engine idling, carefully spray a small amount of carburetor cleaner or an unlit propane torch around the base of the intake plenum and vacuum lines. If the engine idle speed changes or smooths out, you've found a vacuum leak.

3. Rule Out Internal Mechanical Problems

If the fuel and air systems check out, the issue might be internal engine damage.

Perform a Compression Test: This test measures the internal pressure created by the piston and is crucial for diagnosing engine health. Compare the reading for cylinder 4 to the other cylinders. A significantly lower reading (e.g., 70 psi vs 140-150 psi in others) indicates a mechanical problem.

Consider Common Dodge Issues: TheDodge 3.6L engine, in particular, has known problems with exhaust valves not seating properly, which causes low compression. Low compression can also be caused by worn piston rings or a blown head gasket.

By following these diagnostic steps, you can pinpoint the exact cause of the misfire in your Dodge Caravan.