During a recent analysis of inoperative ignition modules, a dealer submitted an alternate test procedure for diagnosing HEI ignition modules. The test described below requires the use of only three jumper leads and a 12V electrical test light. It is presented here for use when an approved module tester, such as the Kent-Moore tester J-24642-F, is damaged or otherwise unavailable. Use of an approved module tester is still recommended as the primary diagnostic tool for ignition modules. Refer to Section 6E-C4, "Electronic Spark Timing (EST) System" and Section 6D4, "Ignition System" of the appropriate model year Service Information Manual for additional information.
ON-CAR HEI MODULE TEST CADILLAC DFI MODELS ONLY
Previous bulletins on this subject, such as T-86-79, have described detailed procedures for diagnosis and repair. Most important among these procedures is the requirement that when distributor driven gear wear is discovered, the distributor drive gear (camshaft) must also be replaced. The reason for this is that the two gears wear together in a pattern and when only one of the pair is replaced the likelihood of a repeat failure is very high.
In spite of this requirement, Cadillac continues to receive warranty claims indicating that only the distributor driven gear was replaced. In the interest of customer satisfaction, Labor Operation J4520-B (Distributor Driven Gear Replacement) has been cancelled. Operation T6135 described in Bulletin T-86-79 must be used for this repair.