Repeated "No Mag Interface" Shutdowns Caterpillar

Reference: SEPTEMBER 24, 1997 ENGINE TIB, COMPONENT CODE 1900, REPEATED "NO MAG INTERFACE" SHUTDOWNS

Problem:

The continued reports of nuisance "No Mag Interface" shutdowns was previously identified as:

* The "F9" light is activated on the Engine Supervisory System (ESS) control panel.

* The "No Magneto Interface Signal" light is activated on the Timing Control Module (TCM).

* Diagnostic Code (326-09) is activated on the Digital Diagnostic Tool (DDT).

The "No Mag Interface", (326-09) is activated by the Timing Control Module when no ignition pulses are received from the Magneto Interface Box. This diagnostic is only detected when the engine is started and the speed is between 120 and 300 rpm. If no ignition pulse is detected for 500 milliseconds after the engine speed is greater than 120 rpm and less than 300 rpm, the engine is shut down.

Three potential situations could cause this problem, all of which will decrease speed sensor signal strength.

* Ground reference differences between the Timing Control Module (TMC) and the ignition system.

* Increasing the temperature of the speed sensor.

* Increased gap between the sensor and ring gear caused by the sensor being set incorrectly or the ring gear being out of round.

Solution:

Because the ignition pulses are present when the shutdown occurs, these nuisance shutdowns appear to be the result of: system grounding; the voltage threshold in the Timing Control Module; and/or the voltage levels generated by the Magneto Interface Box.

A permanent fix is being worked on and will be released when identified.

An interim fix that will reduce the frequency of these nuisance shutdowns follows:

Use an 18 gauge wire to connect the terminal 545 (located on the door of the ESS panel) to terminal 354 or 353 [battery negative (located on the lower right corner of the ESS panel box)]. Reference a 3E-9347 or 128-2508 Electrical Wiring Diagram for In-Line engines. Reference a 3E-9348 or 128-3198 Electrical Wiring Diagram for Vee engines.

Another temporary solution is to utilize a speed sensor on the Timing Control Module (TCM) with a stronger output signal at low speeds. The 7X-1168 Speed Sensor has approximately twice the signal strength of the current 8L-4171 Speed Sensor and has been successfully tested as a solution. The existing TCM 8L-4171 Speed Sensor can be directly replaced with a 7X-1168 Speed Sensor to help correct "No Mag Input" shutdowns.

NOTE: To adjust the speed sensor, turn the speed sensor in until it makes contact with the flywheel ring gear. Then turn the speed sensor out one full turn and lock in position. Slowly turn the flywheel one full revolution to insure that the speed sensor does not contact the ring gear.

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