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401 running rough


Robert Ricci

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If it is a miss. Like one plug isn't firing. Pull one plug wire off at a time with the car running. If you have one dead cylinder you'll be able to find it. Best to use spark plug boot pliers. Be careful when doing it. You can get a little shock. If you notice a change in idle when you pull the boot off of the spark plug. Then that plug is firing. If you don't have a change. Then that plug is not firing. Diagnose from there. Fouled plug, damaged plug or wire. It can be so many things to cause a rough idle. Like carburetor, vacuum leak, valve train issue, bad plug or wire, or just timing. If it sounds like a miss. And you just did a tune up. Maybe the gap is off on one plug.

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Bob,

The idea to narrow it down to a particular cylinder is a good one, but there is a way to keep yourself from getting zapped. When you remove the spark plug wire, make sure that you are NOT touching ANY part of the car with your body! Not even leaning against the fender!

A quick way to tell if the spark plug wire(s) are arching to ground is to open the hood at night in a very dark place while the engine is running. You may see little blue streaks arching from the wires or boots to ground. Sometimes a spray bottle with plain tap water can help to locate the bad wire just by spraying the plug wires while the engine is running.

Keep us posted!

Tim

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