This means that the spark plugs fire in that order, starting with cylinder #1 and ending with cylinder #4.
To determine which cylinder is #1:
* Locate the distributor cap.
* Look for a mark or number "1" on the cap.
* The cylinder that the #1 spark plug wire is connected to is cylinder #1.
If you're unsure about any aspect of working on your vehicle, it's always best to consult a qualified mechanic.
