Coil Pack Trace

Tech Note 014:

DUAL PLUG IGNITION: 1991 Ford Ranger 2.3L EFI 

Comparison primary current waveforms of the left and right side coil packs.

The DIS module in this system uses four power transistors one for each primary winding. Figure #1 testing primary current with low amp prob. The right side coil pack in this system is responsible for firing the air/fuel mixture that makes the power. Red trace, #1 primary winding. Blue trace, #2 primary winding. Both winding and power transistors are good in this coil pack. The primary windings are pulling 5.2 amps probe conversion is 100mv=1amp.

Figure #2 left side coil pack. This side is responsible for emissions reduction. Blue trace, #1 primary winding shows high resistance problem leading edge. Trailing edge looks normal. Red trace, #2 primary winding leading edge looks normal trailing edge is the one with the problem. I suspect that the transistor is partially shorted. The NPN transistor completes the circuit by grounding the primary winding and charging the coil. As the coil charges the magnetic field builds, the transistor then opens the circuit, the field collapses rapidly, and induces the high voltage in the secondary winding plug fires. Looking at the trailing edge you can see a glitch and a sloping down to zero amps. This glitch is setting trouble code #18 in memory erratic input to ECA. This code in memory on dual plug systems puts the ECA into FMEM or limp in mode.