A number of manufacturer's now produce adjustable advance timing lights. Coupled with inductive pick-ups, this has made the timing light a valuable diagnostic tool as well as a a service item.
Most vehicles have a very prominent timing mark at Top Dead Center (TDC) and usually one or more at various degrees of advance for ignition settings. Unfortunately, many aren't marked, or have multiple markings for various applications. Some may have markings for things other than ignition, for example FI settings. Add the risk on an older engine that the pulley may have been changed to an incorrect pulley, and you have potential for error.
Inductive pickup means there is a clamp-on sensor that triggers the light. No more jury rigs and exposed connection to pop you with 10K volts! You clamp it on #1 plug wire and adjust the normal way.
However, you can clamp it on any of the others and get a pretty good idea of ignition performance. An erratic light may mean a particular cylinder isn't firing consistently. Burned distributor cap post? Damaged internal wire? Bad plug?
The best method of measuring timing is to use the adjustable feature. This is a model that has a dial at the back where you can set the amount of delay on the strobe flash, thus allowing it to flash at the TDC mark instead of wherever the pulley is at the time. Using 5° BTDC as example, you would crank in 5° on the timing light and it would flash at the original TDC mark (usually the most prominent on the pulley). Thus you are adjusting to the most prominent mark on the pulley, and one that is consistent from vehicle to vehicle.
You can also turn the knob until it does flash at TDC and then read the amount of current advance, so it becomes a diagnostic tool. Coupled with a good diagnostic tach, you can see the effects of timing on idle. Remember, the specs are always at a given RPM and the two are inter-related.
Last edited by Capt. Mike; 02-28-2008 at 07:33 AM.
We've gotten so used to timing lights that the old static method has dropped out of the manuals for later models. Here's a start point so you can at least running enough to use a timing light.
Crank the engine such that #1's firing point is at the case line. This will typically be the idle setting notch on the crank-pulley. Most fire at some set degrees BTDC.
Connect a test light from the #1 terminal on the coil to ground and turn on the ignition. Loosen the lock nut and turn the distributor until the light just comes on. It is imperative that the point gap be already adjusted perfectly. As little .1mm off on the points can change timing 3Â°.