Tech Stuff

Waveform diagnostics: Ignition diagnostics you will actually use

Alex Portillo is the head technician of Car Clinic, a state-of-the-art automotive repair facility in Mahopac, N.Y. He is a protégé of technician Jerry Truglia and has been trained by Automotive Technician Training Service and is Technicians Service Training (TST) certified. Portillo’s real-world, in-depth diagnostic articles will appear in future issues of Auto Service Professional magazine on a regular basis.

Research for this article was conducted by G. “Jerry” Truglia, Craig Truglia and Kevin Quinlan. This is the second in a series of articles begun by Craig Truglia, owner of Car Clinic (see the July/August 2012 issue). Here, Portillo continues with an advanced look on how to diagnose ignition problems. Some of the artwork has been done with the help of Ralph Birnbaum.

We are not going to get into the old stuff here that you’re already well acquainted with. The basic ignition system principles at work in a distributor are no different from those that make a modern coil-on-plug (COP) ignition work. COP, even without a cap and rotor, still:

• charges and fire a coil with a switched circuit;

• needs good power and ground; and

• needs to know engine speed for ignition timing.

Being that pretty much everything has moved over to COP or waste-spark ignition, we are going to cover the essentials on these systems first.

Ignition coils and primary ignition

The one thing that every ignition system has in common is the ignition coil.

A coil is in effect the “middle” of the ignition system. Every component in the ignition system leading up into the coil is primary ignition. If you want to get real technical, there is a metal coil with a carbon bar in the middle in the first part of the coil. Secondary ignition is every part after the coil. Again, technically speaking there is a second set of winding, in the second half of the coil.

In Figure 1 we can see the infamous 2000’s era Ford ignition coil. Circled is the primary connection section of the coil, which can be diagnosed by probing the ground side of the connector with a labscope.

Figure 1: The infamous 2000’s era Ford ignition coil. Circled is the primary connection section of this troublesome coil design.
<p>Figure 1: The infamous 2000’s era Ford ignition coil. Circled is the primary connection section of this troublesome coil design.</p>

Swapping coils and just looking at misfire counter on Mode 6 or checking for misfire DTCs is a common, but less precise, practice. Personally, we sell the customer on all new ignition coils or threaten them with diagnostic costs to pick out the bad ones. That seems to do the trick.

Every coil, no matter the vehicle, needs power. So anything that inhibits the coil getting power will compromise its performance. Be sure to check for the following:

• Correct voltage — A voltage drop to the coil can make it ineffective.

• Good switching — If the “switch” wherever it’s location (points, ICM, D.I.S, PCM these days, etc.) contact has high resistance, or if the ground connection is bad, power to the coil is reduced, weakening the spark.

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