GM High Energy Ignition With Internal Coil

Even though this ignition system has been around since 1974, not everyone working on vehicles today may have seen this system before. Whether or not that be the case, here are a few tips that we have seen cause ignition failures and may prevent you from inheriting one. When installing the coil inside of the cap, there are several steps you need to take to ensure proper performance. Since 1974 this coil has undergone some design changes. The first design used an internal ground, which connected the secondary coil winding to the primary coil. This design did not isolate the secondary circuit sufficiently, so an additional ground wire which connected the secondary coil to the laminate frame was added. The latest design now has an isolated secondary circuit that is very similar to the distributorless systems in use today.

Critical to this design change is the ground strap which must be installed under the coil inside of the cap. Without the ground strap, the frame of the coil will become charged with secondary voltage. Because of this, arcing will occur from the frame to any electrical path leading to the other end of the secondary circuit. This path may include the primary wiring. If this happens, the high voltage leak could destroy the module, ECM, and in some cases even melt the distributor cap. A second point of concern with this system is the polarity of the coil. There are two coils which have different polarity and they are not interchangeable. These two coils can be distinguished by the primary lead colors. One has red and white leads, while the second has red and yellow leads. Coil polarity is important because the magnetic field generated by the coil must match the magnetic field of the distributor pick-up. Using mismatched parts can create a driveability problem as well as a no spark condition. The conflicting magnetic fields may lower the output signal from the pick up coil to the point where the module will not recognize the signal. The way to determine if you have the correct part is to consult the parts catalog. However, if you cannot do that, the best way to make sure you have compatible parts is to check the distributor pick-up connector color. A yellow connector means that the matching coil must have a yellow lead. If the connector is a color other than yellow, then the matching coil must have a white lead.

You should always use the mounting screws that are supplied with the coil. There are different versions of this coil; some may actually differ in mounting height. If you reuse the old screws with the new coil, they might be too long. In this situation, they may actually protrude through the bottom of the cap, providing a ground path for secondary voltage, which will create ignition problems. On a final note, make sure that the primary leads are properly routed and are not pinched when the top is installed.

Jeff Auerbach

Domestic Specialist