Modern Ignition Systems
UNDERSTANDING MODERN DAY
IGNITION SYSTEMS
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Tips for diagnosing popular systems There have been many enhancements on today’s modern day ignition systems so as to make the modern day technician’s job easier of investigating the popular misfire code or a misfire symptom without a misfire code. Normally with a misfire code or a misfire symptom, most technicians initially suspect an ignition problem such as a bad coil, a faulty secondary lead or a bad spark plug. As we all know, you cannot undermine what you feel through the seat of your pants when doing a test drive and experience what you initially think is a misfire.
By Bill Fulton
Always take along a scan tool and record the data when the symptom occurs. A GM vehicle we serviced recently exhibited the exact symptoms of a jerk and buck that we feel during a misfire event. There was no MIL and no codes. Note Figure 1. The scan tool is set up to do a snapshot record. We are using the graphing mode of the scan tool as we recall the 10 second record. Notice the bottom graph. The 02 sensor values are being graphed out as well as the integrator values now known as short term fuel trim. If an ignition-related misfire had occurred we would have seen the O2 voltage go momentarily ALL ART COURTESY OF BILL FULTON
Figure 1: The scan tool is set up to do a snapshot record. Notice the bottom graph. The O2 sensor values are being graphed out as well as the integrator values (short term fuel trim).
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ASP
Februa ry 2 0 20
