Engine Controls - System/component Tests - 4.0L: Other Jeep Cherokee II

ELECTRONIC CONTROL UNIT (ECU)

For diagnosing electronic control system malfunctions, refer to TESTS W/CODES article. For testing ground and power circuits of ECU, use the following procedures. If necessary, refer to ECU control schematics. see scheme 2and see scheme 3.

GROUND CIRCUITS

1. Using an ohmmeter, check for continuity to ground on ECU ground terminals. See ECU GROUND CIRCUITS table. Resistance should be zero ohms. If not, repair open ground circuit.
2. Using a DVOM, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. See ECU GROUND CIRCUITS table. With vehicle running, voltmeter reading should be less than .1 volt. If voltmeter reading is greater than .1 volt, check for open, corrosion or loose connection on ground lead.

ECU GROUND CIRCUITS

Scheme 230

1. Using a voltmeter, check for battery voltage between ECU terminal B-7 and ground. (Scheme 230) If battery voltage is not present, check diagnostic connector No. 1 terminal No. 5 (D1-5) for proper seating. (Scheme 230) If connector is okay, check for an open in Red wire between ECU and D1-5, and between D1-5 and battery.
2. Turn ignition switch to the ON position. Using a voltmeter, check for battery voltage between ECU terminal B-8 and ground. (Scheme 230) If battery voltage is not present, check for an open in Yellow wire between ignition switch and terminal B-8 of ECU, or check for a defective ignition switch.
3. Connect a voltmeter between ground and ECU terminal C-3. (Scheme 230) Turn ignition switch to the START position. Battery voltage should be present between control unit terminal C-3 and ground ONLY when ignition switch is in the START position. If voltage is not present, check for an open in Green wire between ECU terminal C-3 and start relay, or check for a defective start relay or ignition switch.

EVAPORATIVE FUEL SYSTEM

To test fuel evaporation system, refer to TESTS W/CODES article.

FUEL DELIVERY

Note. For fuel system pressure testing, see F BASIC TESTING article in this section.

OXYGEN (O2) SENSOR HEATING ELEMENT

Note. For additional oxygen sensor information, see TITANIA OXYGEN SENSOR TESTING article.

SPARK PLUG CHECK

Faulty or fouled plugs may perform well at idle speed, but at higher engine speeds, they frequently fail. Faulty plug can exhibit the following symptoms

1. Poor fuel economy.
2. Power loss.
3. Decreased engine speed.
4. Hard starting.
5. Generally poor performance.

Spark plugs also malfunction due to carbon fouling, excessive electrode air gap, or broken insulators.