Q: I have a 2008 2WD Dodge Ram 1500 with the 4.7-liter V-8 and 65,000 miles. It's missing on cylinder #7 and I have trouble codes P0300 and P0207. I swapped the ignition coils, wires, and injectors, but it's still there. There is spark at the plugs. Could it be a camshaft problem, or something else mechanical?

A: No -- DTC P0300 is a multiple-cylinder misfire code caused by the misfire at cylinder #7. Technically, you should get DTC P0307, which specifically indicates the cylinder 7 miss, but these systems weren't so smart. A newer truck probably would've produced the P0307. But P0207 is the one you need to focus on. This one indicates a circuit failure at the #7 fuel injector. So don't worry about a mechanical engine problem.

The first step would be to test the resistance of the fuel injector itself, but if you swapped the #7 injector with one from another cylinder, and still had a misfire at #7, you accomplished the same thing. This concludes the injector is not the problem. Next would be a quick test with a tool known as a "noid light."

It's simply a high-impedance test light that can check the circuits to the injector without risking damage to the powertrain control module. If you plug the noid light into the injector connector, start the engine, and the light does not flash, you know the problem is in the circuit(s) powering the injector. In this case, it can be an open in the 12-volt circuit from the power module to the injector or the PCM, or an open or short in the ground circuit from the PCM, which pulses the injector on and off. Or, worst-case scenario, there's a bad injector driver inside the PCM, which will require PCM replacement. Testing these circuits accurately will require the correct wiring schematic, a digital multimeter, and significant experience in continuity, voltage drop, and ohms law.