TESTING
Primary and Secondary Circuit Tests
- Turn the ignition switch OFF , disconnect the battery, then detach the wiring harness connector from the ignition coil to be tested.
- Check for dirt, corrosion or damage on the terminals.
See Figures 1 and 2
- Use an ohmmeter to measure the resistance between the following terminals on the ignition coil, and note the resistance:
2.3L, 2.5L and 5.0L engines
or,
The resistance between all of these terminals should have been between 0.3-1.0 ohms. If the resistance was more or less than this value, the coil should be replaced with a new one.
SECONDARY RESISTANCESee Figures 1 and 2
Fig. Fig. 1: Engine ignition coil harness connections-3.0L and 4.0L engines
Fig. Fig. 2: Engine ignition coil harness connections-2.3L, 2.5L and 5.0L engines
- Measure, using the ohmmeter, and note the resistance between each corresponding coil terminal and the two spark plug wire towers on the ignition coil. The coil terminals and plug wires towers are grouped as follows:
2.3L, 2.5L engines-right-hand coil pack
2.3L, 2.5L engines-left-hand coil pack
5.0L engines-right-hand coil pack
5.0L engines-left-hand coil pack
If the resistance for all of the readings was between 6,500-11,500 ohms, the ignition coils are OK. If any of the readings was less than 6,500 ohms or more than 11,500 ohms, replace the corresponding coil pack.
On 2.3L, 2.5L and 5.0L engines, if one coil pack is found to be defective, the other pack does not need to be replaced.
REMOVAL & INSTALLATIONSee Figures 3 through 12
All engines, except the 2.3L, 2.5L and 5.0L engines, utilizes one coil pack containing three separate coils. The 2.3L, 2.5L and 5.0L engines use two coil packs containing two separate coils each.
Fig. Fig. 3: 1991 ignition coil mounting for the 2.3L engine
Fig. Fig. 4: 1992-99 ignition coil mounting for the 2.3L, 2.5L engine
Fig. Fig. 5: Ignition coil mounting for the 3.0L engine
Fig. Fig. 6: Ignition coil mounting for the 4.0L engine
Fig. Fig. 7: Ignition coil mounting for the 5.0L engine
- Disconnect the negative battery cable.
Fig. Fig. 8: To remove the coil pack, unplug the electrical harness connector from it
- Unplug the electrical harness connector from the ignition coil pack.
Fig. Fig. 9: Label the spark plug wires according to their position on the coil pack
Fig. Fig. 10: Remove the plug wires from the coil by squeezing the lock tabs (arrows) and pulling straight up
- Label and remove the spark plug wires from the ignition coil terminal towers by squeezing the locking tabs to release the coil boot retainers.
Fig. Fig. 11: Remove the coil retaining screws ...
Fig. Fig. 12: ... then remove the coil pack from its mounting bracket
- Remove the coil pack mounting screws and remove the coil pack.
- Install the coil pack and the retaining screws. Tighten the retaining screws to 40-62 inch lbs. (4.5-7 Nm).
Be sure to place some dielectric compound into each spark plug boot prior to installation of the spark plug wire.
- Attach the spark plug wires and electrical harness connector to the coil pack.
- Connect the negative battery cable.
SERVICE PRECAUTIONS
PRELIMINARY CHECKS
- Visually inspect the engine compartment to ensure that all vacuum lines and spark plug wires are properly routed and securely connected.
- Examine all wiring harnesses and connectors for insulation damage, burned, overheated, loose or broken connections.
- Be certain that the battery is fully charged and that all accessories areOFF during the diagnosis.
See Figures 1 through 12
This is a general system test for a no-start condition. Use the accompanying flow charts for this test. For ignition coil testing refer to the ignition coil procedures.
Most Digital Volt Ohmmeters (DVOMs) used today belong to a class referred to as "averaging." Some averaging DVOMs include the Rotunda® 007-00001, the Fluke® 70, 20 series and the Fluke® 88. Recently a new class of DVOMs, referred to as True RMS DVOMs (such as: the Fluke® 87, 8060A, 8062A, etc.), are being used. True RMS DVOMs should not be used for the tests presented here. They may display different voltage readings depending on whether the DVOM is first turned on and then the test leads are attached, or if the leads are attached first, then the DVOM is turned on. Also they may not auto range to the same range during each test, and some show different values depending on the range selected.
Fig. Fig. 1: Test A-no start, part 1
Fig. Fig. 2: Test A-no start, part 2
Fig. Fig. 3: Test A-no start, part 3
Fig. Fig. 4: Test A-no start, part 4
Fig. Fig. 5: Test A-no start, part 5
Fig. Fig. 6: Test A-no start, part 6
Fig. Fig. 7: Test A-no start, part 7
Fig. Fig. 8: Test B-code 16, memory code 18 and/or "Check Engine Light On" IDM failure
Fig. Fig. 9: Test C-memory code 45 and/or "Check Engine Light On" coil failure, part 1
Fig. Fig. 10: Test C-memory code 45 and/or "Check Engine Light On" coil failure, part 2
Fig. Fig. 11: Test D-engine running with code 18, SAW failure, part 1
Fig. Fig. 12: Test D-engine running with code 18, SAW failure, part 2
The distributorless ignition system used by 1991-94 2.3L and 4.0L, and all 1995-99 engines is referred to as the Electronic Ignition (EI) system. It eliminates the conventional distributor by utilizing multiple ignition coils instead. The EI system consists of the
REMOVAL & INSTALLATION
See Figures 1, 2 and 3
Only the EEC-IV ignition systems use an external ICM. EEC-V systems have incorperated the ICM into the Power Control Module (PCM).
- Disconnect the negative battery cable.
- Detach the wiring harness connector(s) from the ICM.
- Remove the mounting bolts, then remove the ICM.
- Position the ICM onto the inner fender apron and install the mounting bolts. Tighten the bolts to 22-31 inch lbs (2.5-3.5 Nm).
- Attach the wiring harness connector(s) to the ICM.
- Connect the negative battery cable.
Fig. Fig. 1: Ignition control module and mounting location on the 2.3L, 2.5L engine
Fig. Fig. 2: Ignition control module used on all EEC-IV systems except the 2.3L engine
Fig. Fig. 3: Ignition control module mounting on all EEC-IV systems except the 2.3L engine
following components:
The function of the ICM was incorporated into the PCM beginning with the EEC-V system; otherwise the newer system operates in the same manner.
SYSTEM OPERATIONThe CKP sensor is a variable reluctance sensor, mounted near the crankshaft damper and pulley.
The crankshaft damper has a 36 minus 1 tooth wheel (data wheel) mounted on it. When this wheel rotates the magnetic field (reluctance) of the CKP sensor changes in relationship with the passing of the teeth on the data wheel. This change in the magnetic field is called the CKP signal.
The base ignition timing is set at 10 (plus or minus 2 degrees) degrees Before Top Dead Center (BTDC) and is not adjustable.
EEC-IV SystemsSee Figure 1
The CKP signal is sent to the ICM, where it is used to create the Profile Ignition Pick-up (PIP) signal.
The one missing tooth on the data wheel creates one large space between two of the teeth. The ICM utilizes this large space as a reference to help determine base ignition timing and engine speed (rpm), and to synchronize the ignition coils for the proper spark timing sequence.
Fig. Fig. 1: Common wiring schematic for an EEC-IV distributorless ignition system
The PIP signal is sent from the ICM to the PCM, which will use the PIP signal to determine base ignition timing and rpm calculations.
The ICM also receives the Spark Angle Word (SAW) signal from the PCM, which is used by the ICM to calculate the proper spark timing advance. Once all of the signals are calculated, the ICM determines the proper ON and OFF timing for the ignition coils.
The 4.0L engine utilizes one ignition coil pack, which contains three separate ignition coils. Each ignition coil fires two spark plugs simultaneously. One of the two plugs being fired is on the compression stroke (this plug uses most of the voltage) and the other plug is on the exhaust stroke (this plug uses very little of the voltage). Since these two plugs are connected in series, the firing voltage of one plug is negative (with respect to ground) and the other plug is positive.
If, for some reason, a fault arises in the EI system, the Failure Mode Effects Management (FMEM) portion of the ICM maintains vehicle operation. If the ICM stops receiving the SAW input signal, it will directly fire the ignition coils based on the CKP signal. This condition results in a fixed timing of 10 degrees BTDC.
EEC-V SystemsThe CKP signal is sent to the PCM, which uses the signal to determine base ignition timing and rpm calculations.
The one missing tooth on the data wheel creates one large space between two of the teeth. The PCM utilizes this large space as a reference to help determine base ignition timing and engine speed (rpm), and to synchronize the ignition coils for the proper spark timing sequence.
All engines, except the 2.3L, 2.5L and 5.0L engines, utilize one ignition coil pack, which contains three separate ignition coils, whereas the 2.3L, 2.5L and 5.0L engines use two separate ignition coil packs, each of which contains two ignition coils. Each ignition coil fires two spark plugs simultaneously. One of the two plugs being fired is on the compression stroke (this plug uses most of the voltage) and the other plug is on the exhaust stroke (this plug uses very little of the voltage). Since these two plugs are connected in series, the firing voltage of one plug is negative (with respect to ground) and the other plug is positive.
