Engines General Information
2.5L CRANKSHAFTA new crankshaft is used in 1988 2.5L engines. The new crankshaft is shorter in length than the previous shaft. A longer crankshaft dampener bolt is required with the new, shorter shaft.
2.4L VALVE SPRINGS
1988, 2.5L engines will be equipped with new design, valve springs (A). The new springs are slightly tapered top-to-bottom and are identified by the two bottom coils (B) which are flush.
New valve spring retainers and keepers (locks) are also used to accomodate the new design valve springs.
The new valve springs can be removed/ installed on the vehicle with service tool J- 5892B. Part number for this tool is 8980 002 694. The tool is available from your PDC as part of the special tool program.
4.0L ENGINE
The 4.0L engine is basically unchanged for the 1988 model year. Refer to the M.R. 279 and the Mot. 1-6 manuals for necessary specifications and service information.
EMISSION MAINTENANCE TIMER AND INDICATOR LIGHT
1988 Cherokee/Wagoneer 49-State and Canada models are equipped with an emission maintenance timer and indicator light. The timer and light are used to alert the owner when oxygen sensor-PCV valve replacement and other scheduled emission maintenance is required.
The indicator light is located in the instrument cluster. The timer is mounted on the dash panel at the passenger side of the vehicle.
The timer (C) is operated by the ignition system. It activates (flashes) the indicator light when vehicle mileage reaches the scheduled maintenance interval of 133,000 kilometers (82,500 miles).
Emission Maintenance Timer Service
The life cycle of the timer coincides with the emission maintenance interval of 133,000 kilometers (82,500 miles). The timer can not be reset after reaching this mileage interval. The timer can only be replaced or disconnected.
NOTE: The oxygen sensor and timer are interdependent. If the timer should fail prematurely, the oxygen sensor must be replaced along with the timer. This is important in preserving the correct sensor replacement interval and ensuring proper engine performance.
Emission Maintenance Timer Replacement
On models with cruise control, remove the module attaching screws (A) and remove cruise control module (B).
Remove the screws attaching the maintenance timer (C) to the dash bracket and remove the timer from the bracket.
NOTE: The maintenance timer is mounted on the dash panel to the right of the steering column.
Disconnect the timer electrical wires (D) and remove the timer from the vehicle.
Connect the electrical wires to the timer.
Position the replacement timer on the dash bracket and install the timer attaching screws.
Install the cruise control module.
4.0L ENGINE EGR SYSTEM
EGR System Components
The EGR system on 1988, 4.0L engines consists of the EGR valve (A), a vacuum transducer
(B) and an EGR solenoid (C).
The vacuum transducer is controlled by exhaust back pressure. The transducer is actuated by the solenoid which in turn is operated by the ECU. The ECU allows vacuum to flow through the solenoid when it it is not energized. A more detailed description of the transducer and solenoid functions are provided in the MS 1700 Manual.
Vacuum lines interconnect the valve and transducer and the transducer and solenoid. The electrical portion of the solenoid is connected to the ECU.
EGR Operation
Engine vacuum flows through the EGR solenoid to the vacuum transducer (D) through connecting line (E). Vacuum flow occurs only when the solenoid is not energized (no voltage applied).
The transducer (D) is connected to the EGR valve (F) by vacuum line (G) and back pressure line (H). The transducer is controlled by exhaust back pressure and is ported to the exhaust manifold through line (H).
When the solenoid is not energized and exhaust gas back pressure entering EGR valve inlet (J) is high enough, back pressure holds transducer bleed valve (K) closed. This allows vacuum to activate and operate the EGR valve.
EGR Component Testing
Bring the engine to normal operating temperature.
Operate the engine at curb idle speed.
Test the EGR solenoid as follows:
^ Check vacuum at solenoid line (1). Disconnect the line and attach a vacuum gauge to it.
^ Vacuum should be a minimum of 15 inches.
^ If vacuum is low, check the line for kinks, twists, or a loose connection at manifold fitting (2).
^ If vacuum is OK, remove gauge, reconnect the line and proceed to next step.
^ Check vacuum at solenoid vacuum line connector (3).
^ Disconnect the line and attach a vacuum gauge to connector (3). Vacuum reading should be zero (no vacuum) at this side of solenoid.
^ If vacuum reading is zero, leave the gauge attached and proceed to next step. However, if vacuum is present, check solenoid/ECU operation with the MS 1700 tester and repair as necessary.
^ Disconnect electrical wire (4) and note vacuum at connector (3). Vacuum should now be present at connector (3).
^ If vacuum is present, proceed to EGR valve test.
^ If vacuum is not present, replace the solenoid.
Test the EGR valve as follows:
^ Leave solenoid wire (4) disconnected. Then connect the vacuum line to solenoid connector (3) and note engine idle.
^ The engine should now idle roughly or stall. If this occurs, the valve is OK. Proceed to the vacuum transducer test.
^ If idle does not change, disconnect EGR vacuum line (5) and connect a hand vacuum pump (such as tool J-23738-A) to EGR valve nipple (6).
^ Apply a minimum of 12 inches vacuum to the valve and note engine idle. If engine now idles roughly or stalls, proceed to next step.
^ If engine idle did not change, reconnect the vacuum hose and note idle. If idle remains unchanged, test the transducer.
Test the vacuum transducer as follows:
^ Disconnect the transducer vacuum lines and remove the transducer (7) from the vehicle.
^ Plug transducer port (8).
^ Apply 1-2 pounds air pressure to transducer port (10) to simulate exhaust back pressure. Air pressure can be applied with a handoperated air pump, compressed air, or lung power.
^ Apply a minimum of 12 inches vacuum to port (9).
^ Replace the solenoid if will not hold vacuum.