Ignition System Tests - 4.0L: Diagnosis Jeep Cherokee II

BASIC DIAGNOSTIC PROCEDURES

This section contains information for determining individual system component performance. Diagnosis of ECU/Engine Control System is performed using the DRB-II Diagnostic Tester. See the appropriate Computerized Engine Control System article in this section.

COOLANT TEMPERATURE SENSOR (CTS) TEST

1. Disconnect the CTS wire harness connector from the CTS. see scheme 13
2. Using a high input impedance (digital) volt-ohmmeter, test the resistance of the sensor. Resistance should be less than l000 ohms with a warm engine. Refer to the «COOLANT TEMPERATURE SENSOR (CTS) RESISTANCE VALUES»(ref-24456-S39470452072001040200000) table below. COOLANT TEMPERATURE SENSOR (CTS) RESISTANCE VALUES Degrees F° Degrees C° Resistance (Ohms) -40 -40 100,700 0 -18 25,000 20 -7 13,500 40 4 7,500 70 20 3,400 100 38 1,600 160 70 450 212 100 185
3. If any resistance is not within the range as specified in the table, replace the coolant temperature sensor.
4. Test the resistance of the wire harness between the ECU wire harness connector terminal "D-3" and the sensor connector terminal "C-lO".
5. Repair any open circuits.

MANIFOLD AIR TEMPERATURE (MAT) SENSOR TEST

1. Disconnect the MAT wire harness connector from the MAT sensor. see scheme 14*.
2. Using a high input impedance (digital) volt-ohmmeter, test the resistance of the sensor. Resistance should be less than l000 ohms with a warm engine. Refer to the «MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR RESISTANCE VALUES»(ref-24456-S34995881072001040200000) table below. MANIFOLD AIR/FUEL TEMPERATURE (MAT) SENSOR RESISTANCE VALUES Degrees F° Degrees C° Resistance (Ohms) -40 -40 100,700 0 -18 25,000 20 -7 13,500 40 4 7,500 70 20 3,400 100 38 1,600 160 70 450 212 100 185
3. If any resistance is not within the range as specified in the table, replace the MAT sensor.
4. Test the resistance of the wire harness between the ECU wire harness connector terminal "D-3" and the sensor connector terminal "C-8".
5. Repair as necessary any circuits displaying a value greater than one ohm.

Scheme 232

1. Inspect the MAP sensor vacuum hose connections at the throttle body and the MAP sensor. (Scheme 232) Repair vacuum hose or connections as necessary.
2. With the ignition switch ON and engine OFF, test the MAP sensor output voltage at the MAP sensor connector terminal "B". (Scheme 232) With a hot idle condition, the voltage reading should drop to between 0.5-1.5 volts.
3. Test ECU terminal "C-6" for the same voltage as described in step 2) to verify the wiring harness. Repair as necessary.
4. Test the MAP sensor supply voltage at the sensor connector terminal "C" with the ignition ON. Voltage reading should be between 4.5-5.5 volts. Check that the voltage reading at terminal "C-14" is also 4.5-5.5 volts.
5. Repair or replace the wire harness as necessary.
6. Test the MAP sensor ground circuit at the sensor connector terminal "A" and ECU connector terminal "D-3". Repair the wire harness as necessary.
7. Using an ohmmeter, test the MAP sensor ground circuit at the ECU connector between terminal "D-3" and terminal "B-ll". If an open circuit is indicated, check for a defective sensor ground connection. The MAP sensor ground is located on the right side of the engine block.
8. If, after performing step 7), the ground connection is verified to be good, check for a short to 12 volts at terminal "D-3". If a short is found, repair the short and then replace the ECU.

KNOCK SENSOR TEST

1. Connect Diagnostic Tester M.S. 1700 to the vehicle.
2. Go to "State Display" mode.
3. Start the engine and let idle.
4. Observe knock sensor value.
5. Using the tip of a screwdriver, lightly tap the cylinder block near the sensor while observing the knock sensor value.
6. The knock sensor value should increase when the cylinder block is tapped.
7. If the knock sensor value does not increase while tapping on the cylinder block near the knock sensor, check for proper connections to the knock sensor. If connections are good, replace the knock sensor. Refer to REMOVAL & INSTALLATION in this article.

ENGINE SPEED SENSOR TEST

1. Disconnect the engine speed sensor connector from the ignition control module.
2. place an ohmmeter between terminals "A" and "B" (marked on the connector). On a hot engine, the resistance reading should be between 125-275 ohms.
3. Replace sensor if readings are not within specification.

Scheme 233

SYNC PULSE SIGNAL GENERATOR (STATOR) TEST

Note. For this test, an analog voltmeter MUST be used.

1. Insert the positive (+) lead of the voltmeter into the Blue wire at the distributor connector.
2. Insert the negative (-) voltmeter lead into the Gray/White wire at the distributor oonnector. CAUTION: DO NOT remove the distributor connector from distributor. Insert the voltmeter leads into the backside of the distributor connector to make contact with the terminals.
3. Set the voltmeter to the 15-Volt A/C scale. Turn ignition key to "ON".
4. The voltmeter should display approximately 5.0 volts.
5. If no voltage displays, check that the voltmeter leads are making good contact. If there is still no voltage, go to next step.
6. Remove the ECU and check for voltage at pin "C-16" and ground with harness connected. If there in still no voltage, proceed to the next step.
7. Connect Diagnostic Tester M.S. 1700 to the vehicle. Using the diagnostic tester, perform vehicle test. If voltage is present, go to the next step.
8. Check for continuity between the Blue wire at the distributor connector and pin C-16 at the ECU.
9. If there in no continuity, repair harness as necessary.
10. Check Sor continuity between the Gray/White wire at the distributor connector and pin C-5 at the ECU.
11. If there is no continuity, repair harness as necessary.
12. Check for continuity between the Black wire at the distributor connector and ground.
13. If there is no continuity, repair harness as necessary.
14. While observing the voltmeter, crank the engine; the voltmeter needle should fluctuate back and forth while the engine in cranking. A fluctuation verifies that the stator in the distributor is operating properly.
15. If there is no pulse sync, replace the stator. Refer to «REMOVAL & INSTALLATION»(ref-24456-S08696187092001040200000) .