FixVault
Home › American Motors › 1983 › Spirit DL, Automatic, 904 › Repair and Diagnosis › Engine Performance › System › 4.2L Feedback Carburetor System › Testing › Test No 3 - Open Loop Switch Test

Test No 3 - Open Loop Switch Test

NOTE: Engine should be at normal operating temperature. All continuity testing should be done with MCU disconnected. Continuity should be 2 ohms when MCU is disconnected. All continuity should indicate less than one ohm when applicable. Diagnostic connector terminals can be used as test point instead of MCU harness connector terminals.
NOTE: Switch No. 1 is the Green colored port vacuum switch (4 in. Hg vacuum). Switch No. 2 is the Natural colored adaptive switch (10 in. Hg vacuum).
  1. Turn engine off. Using a standard volt-ohmmeter, test for continuity from the diagnostic connector pin 15 to MCU connector J2, pin 1. If the circuit is open, go to step 3). If not, disconnect the vacuum hose from switch 2 of the vacuum switch assembly.
  2. If there is trapped vacuum, repair malfunction and repeat the test. If not, disconnect the vacuum switch assembly wire connector and retest. If circuit is open, replace the vacuum switch assembly and retest. If not, disconnect the MCU harness connector and retest. If circuit is open, replace the MCU and retest. If not, repair harness short circuit between vacuum switch assembly and retest.
  3. Test for continuity between diagnostic connector pin 12 and MCU connector J2, pin 1. If there is an open circuit, go to step 4. If circuit is not open, check if engine is warm. If yes, go to step 4. If not, disconnect coolant temperature switch connector and retest. If circuit is open, replace coolant temperature switch and retest. If not, disconnect MCU connector and retest. If circuit is open, replace MCU and retest. If circuit is closed, repair harness short circuit between coolant temperature switch and MCU and retest.
  4. Test continuity between diagnostic connector pin 9 and MCU connector J2 pin 8. If circuit is open, go to step 5. If not, disconnect the vacuum supply hose from vacuum switch 1. If there is trapped vacuum, repair vacuum malfunction and retest. If there is no vacuum, test for continuity between diagnostic connector pin 9 and vacuum switch connector pin 8. If circuit is open, replace vacuum switch assembly and retest. If not, replace MCU and retest.
  5. If diagnostic connector pin 9 and MCU connector J2 pin 8 circuit was open in step 4, test continuity between diagnostic connector pin 5 and MCU connector J2 pin 1. If circuit is open, go to step 6. If not, check to see if vehicle is equipped with altitude jumper wire. If not, go to step 7. If it is, determine whether wire is incorrectly connected. If so, disconnect and retest. If not, disconnect MCU and retest.
  6. Check to see if vehicle is equipped with altitude jumper wire. If yes, connect altitude jumper wire at MCU. If circuit is open, repair and retest. If not, go to next step.
  7. Test continuity between diagnostic connector pin 10 and MCU connector J2 pin 1. If circuit is open, go to step 9. If not open, disconnect TES wire connector at air cleaner and retest. If circuit is not open, go to next step. If circuit is open, check if air cleaner temperature is above 56°F (13°C). If not, allow air cleaner to heat up and retest. If yes, replace TES and retest.
  8. Disconnect MCU connector and retest. If circuit is open, replace MCU and retest. If not, repair short circuit in TES wire and retest.
  9. Test for continuity between diagnostic connector pin 6 and MCU connector J2, pin 1. If the circuit is open, go next step. If not, disconnect WOT switch connector at carburetor and retest. If circuit is open, replace WOT switch and retest. If not, disconnect MCU and retest. If circuit is open, replace MCU and retest. If not, repair short in WOT switch wire harness.
  10. Depress accelerator pedal to wide open throttle position monitoring continuity between diagnostic connector pin 6 and MCU connector J2 pin 1. If circuit is not open, go to step 12. If circuit is open, inspect carburetor linkage and ensure switch is being engaged.
  11. If not, repair and retest. If yes, disconnect WOT switch connector and connect jumper wire between wiring harness connector terminals. Retest for continuity. If circuit is open, repair open in WOT switch wire and ensure there is continuity between WOT switch and MCU connector J2 pin 10. If circuit is not open, connect a replacement switch to the wiring harness and retest.
  12. Start engine and allow to warm for 3-6 minutes. Turn engine off and test for continuity between diagnostic connector pin 12 and MCU connector J2 pin 1. Circuit should be closed. If yes, go to step 14. If not, go to next step.
  13. Connect jumper wire between coolant temperature switch connector terminals (harness side) and recheck pin 12 on diagnostic connector and MCU connector J2 pin 1 for closed circuit. If yes, replace coolant switch and retest. If not, repair continuity problem in coolant switch circuit. Ensure that continuity also exists at MCU connector J2 pin 6, and recheck.
  14. Start engine. Remove throttle from fast idle cam position and allow engine to return to normal idle speed. Adjust idle if necessary. Turn engine off. Test continuity between diagnostic connector pin 15 and MCU connector J2 pin 1. Check that ported vacuum is at switch 2 (4 in. Hg switch). If circuit is open, go to next step. If not, go to step 17.
  15. If circuit is open, remove vacuum hose from 4 in. Hg switch and install hand vacuum pump. Increase vacuum to 4 in. Hg while testing continuity between diagnostic connector pin 15 and MCU connector J2 pin 1. Continuity should exist.
  16. If yes, test continuity between diagnostic connector pin 9 and MCU connector and place a jumper wire between pins A and B of vacuum switch connector harness side and retest continuity between connector 9 and MCU connector J2 pin 1. If circuit is not open, replace vacuum switch assembly and retest. If open, disconnect MCU connector and retest. If open, repair circuit in wiring harness to vacuum switch. If not, replace MCU and retest.
  17. Disconnect vacuum switch assembly and place jumper wire between pin A and C of vacuum switch connector (harness side) and retest continuity between diagnostic connector pin 15 and MCU connector J2 pin 1. If circuit is not open, replace vacuum switch assembly and retest. If circuit is open, repair open in wiring harness to vacuum switch assembly. Ensure continuity also exists at the MCU connector J2 pin 4.
About FixVault