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Method for Ignition System Testing and Servicing Decisions

IP.com Disclosure Number: IPCOM000074222D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 3 page(s) / 16K

Publishing Venue

IBM

Related People

Briney, LS: AUTHOR [+7]

Abstract

This method is for diagnosis of the spark plugs, spark plug wires, and distributor cap and rotor of an internal combustion engine without disassembly or removal of component parts. The method can be implemented with a computer controlled automobile diagnostic system. A special apparatus produces a controlled high-voltage pulse, similar to the usual pulse from the ignition coil secondary, which is fed to the distributor. The special apparatus also contains detectors and other analog circuitry used to detect voltage on the spark plug wires and the end of each spark plug discharge.

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Method for Ignition System Testing and Servicing Decisions

This method is for diagnosis of the spark plugs, spark plug wires, and distributor cap and rotor of an internal combustion engine without disassembly or removal of component parts. The method can be implemented with a computer controlled automobile diagnostic system. A special apparatus produces a controlled high-voltage pulse, similar to the usual pulse from the ignition coil secondary, which is fed to the distributor. The special apparatus also contains detectors and other analog circuitry used to detect voltage on the spark plug wires and the end of each spark plug discharge.

A computer collects data samples and computes spark plug firing potential, spark line length, and spark line slope. These indicators are measured under two different operating conditions of the engine and if conditions warrant, with a wire pulled and shorted to ground or left open. These indicators are determined from the voltage variations during each spark plug firing in the secondary circuit, which consists of the distributor cap and rotor, the ignition wires and the spark plugs.

The potential is the voltage necessary to initiate the electrical discharge across the spark plug gap. Potential depends upon the gap between the rotor and the cap pin, spark plug wire condition, and spark plug condition.

The spark line length is the time the arc is maintained across the spark plug gap. With constant initial energy, this time is longer with lower resistance, depending on secondary circuit conditions.

The third indicator, spark line slope is a measure of the voltage across the spark plug and wire vs. time, which gives an indication of the resistance in series with the spark plug gap.

The first engine operating condition is at moderate speed (e.g., 1,500 RPM in neutral gear). Samples of potential, length, and slope are taken for a number of firing intervals for each spark plug. The firing potentials are classified into three ranges and are summed for each range. These three sums and the number of potentials in each sum are recorded. The spark line lengths are sorted into three ranges. The number falling in each range is recorded. The spark line slope is determined from voltage samples taken while the plug is firing. Average slope is recorded for each spark plug.

The second engine operating condition is at higher speed, under heavy load (e.g., 2,500 RPM in third gear, at wide-open-throttle with dynamometer loading). This condition causes the engine to heat up more than at the lower speed when it was unloaded, subjecting the ignition system to greater dynamic stresses. Potential, length and slope are recorded in ranges as before, although the ranges may differ from previous ones.

The next step examines data recorded previously and determines if more measurements are required to distinguish between wire and plug faults. Two additional tests may be performed (at moderate engine speed in neutral gear). The fir...