PRELIMINARY GLOW PLUG DIAGNOSIS 1. If system does not operate as described in NORMAL GLOW PLUG CIRCUIT OPERATION, ensure glow plug system is correctly installed. Ensure all connectors are properly attached, clean and tight. Inspect engine harness ground connection. Ensure nut securing 4-wire connector at controller is tightened to 96 INCH lbs. (11 N.M), with connector fully seated and latched. 2. Ensure controller copper stud upper nuts are tightened to 96 INCH lbs (11 N.M). DO NOT tighten lower nuts. Ensure temperature switch connector in water crossover near front of engine is tightened to 48 INCH lbs. (5.4 N.M). Inspect WAIT light on instrument panel for tight connection and operation. INHIBIT SWITCH (BLACK CAP) 1. Remove connector from inhibit switch when engine temperature is less than 100 F (38 C). Inhibit switch is located in water crossover near front of engine. Set ohmmeter on low range. Test continuity across switch terminals. Switch should be closed (a reading of less than one ohm on meter.) 2. Test terminals for continuity to ground with a test light or ohmmeter on high scale. Light should be off. Meter should show greater than one megohm. Replace switch if results are not as specified. 3. Disconnect plug from switch terminals when engine temperature is greater than 125 F (52 C). Change ohmmeter setting to highest scale or use a self -powered test light. Test continuity across switch terminals. Test continuity from each terminal to ground. Switch should be open (test light off or high ohm reading of greater than one megohm on meter). Replace switch if it is closed. When installing replacement switch, tighten to 17 ft. Lbs. (23 N.M). GLOW PLUG SYSTEM DIAGNOSIS Electrical Check Turn ignition off. Disconnect all glow plug connectors. Using an ohmmeter, check resistance between each glow plug terminal and ground. Glow plug resistance should be greater than 2 ohms. Replace glow plug if resistance is not as specified. NO START - COLD Perform these diagnostic procedures if engine does not start when cold; GLOW PLUG light may or may not come on. Before proceeding, check fuel system to ensure it is okay. Ensure battery voltage is 12.4 volts or more with turned ignition off. Ensure cranking speed is at least 100 RPM. 1. With ignition off, measure voltage at battery stud (single wire) on glow plug. See Fig. 6. If voltage is present, go to next step. If voltage is not present, repair battery -to-glow plug controller circuit. 2. If voltage was present in step 1), turn ignition off and measure voltage at glow plug feed stud (twin lead) on glow plug controller. If battery voltage is present, go to next step. If battery voltage is not present, relay contacts are shorted. Replace controller and all glow plugs. 3. If voltage is present in step 2), disconnect harness from all glow plugs. Using an ohmmeter, measure resistance between glow plug terminals and engine block. Replace glow plug if resistance is greater than 2 ohms. Reconnect all glow plugs before continuing with diagnosis. 4. With all glow plugs reconnected, place ignition switch in RUN position. Remove controller connector and check voltage at harness connector terminal "D". See Fig. 6. 5. If no voltage is present, repair open in ignition feed circuit to controller. If voltage is present, measure resistance between terminal "E" of connector and engine block (ground). If measurement is greater than one ohm, repair ground circuit to controller. 6. With ground circuit working properly in step 4), measure resistance between terminals "C" and "E" of connector. If reading is greater than 2 ohms, go to next step. If reading is less than 2 ohms, go to step 8). 7. If reading in step 6) was greater than 2 ohms, check for excessive resistance in voltage sense circuit to controller. Repair as necessary. 8. If reading in step 6) was less than 2 ohms, reconnect controller harness connector and ensure complete engagement. Connector locking latch should click over controller locking tab. With controller connector harness correctly connected, measure voltage at glow plug feed stud (twin lead) on glow plug controller, while turning ignition switch from OFF position to RUN position. 9. If no voltage is present, replace glow plug controller. If battery voltage is present, measure voltage at any one glow plug harness connector when turning ignition switch from OFF to RUN position. Test both right and left banks. 10. If no voltage was present in step 9), repair glow plug feed circuit to glow plugs. If battery voltage is present and instrument panel GLOW PLUG light does not come on, locate and repair bulb or circuit. DIESEL COLD ADVANCE SYSTEM CHECK With ignition on voltage is supplied to cold advance relay through 20-amp GAUGES fuse. When coolant temperature is less than 80 F (27 C), as sensed by coolant temperature sensor, ECM provides a ground at terminal C6. See Fig. 7. Grounding terminal C6 energizes cold advance relay, closing relay contacts and supplying 12 volts to cold advance solenoid (in injection pump), and glow plug controller. Cold advance solenoid is now energized, causing injection pump timing to be advanced about 4 degrees. Cold Advance Relay 1. Disconnect harness connector to cold advance relay. Using an ohmmeter, check resistance between relay terminals "D" and "F". See Fig. 7. Continuity or a resistance of 20 ohms should be present. If not, replace cold advance relay. 2. Using an ohmmeter, check continuity between relay terminals "A" and "E". Continuity should not be present. If continuity is present, replace grounded cold advance relay.
7: Cold Start Advance System Schematic (Typical) Courtesy of GENERAL MOTORS CORP. GLOW PLUG CONTROLLER
Ensure coolant temperature is less than 80 F (27 C) before beginning test. Place ignition switch in RUN position and allow glow plugs to cycle. After 2 minutes, crank engine for one second. It is NOT important that engine starts. Return ignition switch to RUN position. Glow plugs should cycle on at least once.
If glow plugs do not cycle, disconnect controller (controller is located on top rear of valve cover). Connect a 12-volt test light between Purple/White wire terminal of harness connector (terminal "B") and ground. See Fig. 6. With ignition switch in RUN position, test light should be off. Test light should glow when engine is cranked.
If test light does not glow as specified, repair short or open in engine harness Purple/White wire. If test light operates properly but glow plugs do not cycle, replace controller.
Sunday, August 3rd, 2008 AT 8:34 AM