Engine Controls - Adjustments Jeep Wrangler I

ENGINE COMPRESSION

Note. Always refer to Emission Control Label in engine compartment before starting tune-up. If manual and label differ, always use emission label specifications.

Check engine compression with engine at normal operating temperature, all spark plugs removed and throttle valves wide open at specified cranking speed. Ensure battery is fully charged.

ENGINE COMPRESSION TEST

VALVE CLEARANCE

Note. All models use hydraulic lifters. No adjustments are required after initial setting of lash to zero.

2.5L 4-Cylinder

Timing is non-adjustable.

4.0L 6-Cylinder

Timing is controlled by Ignition Control Module (ICM).

4.2L 6-Cylinder

1. Set parking brake. Shift automatic transmission to Park or manual transmission to Neutral. With A/C off, start engine and attain normal operating temperature.
2. With ignition OFF, connect an ignition timing light and a calibrated, expanded-scale tachometer. NOTE: If timing light has an adjustable advance control feature, turn control to OFF position.
3. Disconnect 4 " and 10 " Hg (CEC System) vacuum switch assembly wire connector (located at top of valve cover). Disconnect and plug distributor vacuum advance hose.
4. Start engine, increase engine speed to 1600 RPM and check ignition timing. Adjust timing to specification listed on Emission Control Information label (if necessary). Tighten distributor hold-down clamp and recheck ignition timing.
5. Turn engine off and remove timing light and tachometer. Connect No. 1 spark plug lead, if disconnected. Unplug and connect distributor vacuum advance hose. Connect vacuum switch assembly wire connector.

5.9L V8

1. With parking brake on, transmission in Park and A/C off, warm engine to normal operating temperature.
2. With ignition off, connect timing light and a properly calibrated tachometer. Disconnect and plug distributor vacuum advance hose. Slightly loosen distributor hold down bolt to allow adjustment.
3. With engine idling, check and adjust timing according to specification on Emission Control Information label (if necessary). Tighten distributor hold down clamp and recheck ignition timing.
4. With engine off, remove timing light and tachometer. Reconnect vacuum advance hose.

IDLE SPEED & MIXTURE

Note. Mixture adjustment is NOT a normal tune-up procedure and should not be performed unless mixture control unit is replaced or vehicle fails emissions testing.

Note. Ensure idle speed and timing are set before adjusting idle mixture. If mixture adjustment procedure lasts 3 minutes, run engine at 2000 RPM in NEUTRAL for one minute and resume adjustment.

1. Remove carburetor and locate roll pins blocking idle mixture screws. Drill through throttle body on closed end of roll pin hole. Drive pins out with punch. Install carburetor and connector tachometer.
2. Bring engine to normal operating temperature and adjust curb idle speed to 680 RPM (50 states) or 700 RPM (high altitude). Place automatic transmission in Drive or Neutral for manual transmission. Turn mixture screws inward until RPM drops. Turn screws outward until highest RPM is reached.
3. Turn mixture screws inward until RPM drops to 630 RPM (50 states) or 650 (high altitude). Adjust both screws equally. When mixture is correctly adjusted, replace roll pin to block adjustment screws.

Note. If final RPM differs more than 30 RPM from specified curb idle, reset curb idle and repeat mixture adjustment.

1. Remove carburetor. Remove idle mixture screw tamper resistant caps. Install carburetor. Bring engine to normal operating temperature. With engine running and transmission in neutral, adjust curb idle to 600 RPM.
2. Turn mixture screws clockwise (leaner) until engine speed begins to drop. Then turn screws counterclockwise (richer) until highest RPM reading is obtained for best lean idle. Turn screws clockwise until specified lean drop RPM is obtained (20 RPM). NOTE: If final RPM differs more than 30 RPM from specified curb idle, reset curb idle and repeat mixture adjustment.
3. Carefully install new mixture screw tamper resistant caps. DO NOT move mixture control while installing caps.

Note. On vehicles with fuel injection, air/fuel mixture is controlled by Electronic Control Module (ECM) and is not adjustable. On carbureted models, adjust air/fuel mixture only when vehicle fails emission test or carburetor is disassembled.

IDLE SPEED

THROTTLE POSITION SENSOR (TPS) ADJUSTMENT

Note. All testing procedures are made with engine at normal operating temperature.

2.5L & 4.0L (AUTOMATIC TRANSMISSION)

1. Check TPS input voltage with ignition switch in ON position. Locate square TPS 4-terminal connector marked "A", "B", "C" and "D". DO NOT disconnect connector.
2. Without damaging sensor wires, insert negative voltmeter lead into back of terminal "D" and positive lead into back of terminal "A". Note sensor input voltage reading.
3. Remove voltmeter positive lead from sensor terminal "A" and insert it into back of terminal "B". Note sensor output voltage.
4. Divide output voltage reading by input voltage reading. The desired results should be .825-.835 volt (.830 volt is ideal). Adjust TPS if necessary. NOTE: For example: if input voltage is 5.0 volts and output voltage is 4.15 volts, divide 4.15 by 5 (4.15/5 = .830). The result would be .83 volt.
5. If a large TPS adjustment is necessary, loosen bottom mounting screw and pivot top of sensor until proper reading is achieved. If a fine adjustment is necessary, loosen top sensor mounting screw and pivot bottom of sensor until achieving proper reading. Remove voltmeter.

2.5L & 4.0L (MANUAL TRANSMISSION)

1. Check TPS input voltage with ignition switch in ON position. Locate oval TPS 3-terminal connector marked "A", "B" and "C". DO NOT disconnect connector.
2. Without damaging sensor wires, insert negative voltmeter lead into back of terminal "B" and positive voltmeter lead into back of terminal "A". Ensure throttle plate is completely closed and against idle stop. Note input voltage testing.
3. Remove voltmeter positive lead from terminal "A" and connect it to terminal "C". Ensure throttle plate is completely closed and against idle stop. Note output voltage reading.
4. Divide output voltage reading by input voltage reading. The desired results should be between .825-.835 volt (.830 volt is ideal). Adjust TPS if necessary. NOTE: For example: If input voltage is 5.0 volts and output voltage is 4.15 volts, divide 4.15 by 5 (4.15/5 = .830). The result would be .83 volt.
5. If a large TPS adjustment is necessary, loosen bottom mounting screw and pivot top of sensor until proper reading is achieved. If a fine adjustment is necessary, loosen top sensor mounting screw and pivot bottom of sensor until proper reading is achieved. Remove voltmeter.