Fuel- Do you hear the fuel pump kick on when you just turn the key to on?
Have you tried forcing some (ignitable) spray such as WD-40 into the intake? Is you gas gauge working ok?
Air- Any vacuum lines disconnected? Air filter in good shape?
Spark- did you pull the plugs to make sure you didn't have any serious build-up?
I'm not sure why you replaced some of the components you did. Alternators are to replaced when your battery is not receiving a charge while the engine is running. Crank position sensors tend to be a culprit when it takes more than one crank to start.
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Re: 1987 Cherokee does not start - rolls only
Back to basics.. it turns over? starting system is ok... does it have fuel? does it have spark? is it getting air?....many many vacuum lines in that year model ..any many could be compromised...waft carb cleaner through intake to see if it lights up... check for spark if not .... then continue with compression test for engine internal health and timing issues... too many things to list here.... good luck adn avdive
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Crankshaft position sensor,cam sensor . your vehicle should have coil on plug , a coil at each spark plug !
Each ignition coil has an ignition 1 feed and a ground. The PCM supplies an ignition control (IC) circuit. Each ignition coil contains a solid state driver module as its primary element. The powertrain control module (PCM) signals the coil driver to initiate a firing event by applying a signal to the IC circuit at the appropriate time. When the signal is removed, the coil fires the spark plug. The spark plugs are tipped with platinum for long wear and higher efficiency.
During normal operation the powertrain control module (PCM) controls all ignition functions. If either the crankshaft position (CKP) or camshaft position (CMP) sensor signal is lost, the engine will continue to run because the PCM will default to a limp home mode using the remaining sensor input. As mentioned above, each coil is internally protected against damage from excessive voltage. If one or more coils were to fail in this manner, a misfiring condition would result. Diagnostic trouble codes are available to accurately diagnose the ignition system with a scan tool.
If a crank sensor is replaced a Crankshaft Position System Variation Learn must be done and a scan tool is need to do this.
If the check engine light does NOT come on when cranking at the times
when it won't start, then your ECU is in need of repair. The engine will
only start after the check engine light comes on and the ecu is what
controls that. It's likely going bad, causing the delayed start problem
typical of early 90's jeeps. Repair or replacement services for your
jeep ECU are available on ebay.
The ignition engine speed sensor input signal to Powertrain Control Module (PCM) or Electronic Control Module (ECM) is continuously monitored. The test fails when the signal indicates that 2 successive erratic profile ignition pickup (PIP) pulses occurred.
Symptoms: - Engine Light ON (or Service Engine Soon Warning Light) - Lack/Loss of Power - The engine may be harder to start - The engine may stumble or stall
When is the code detected? The P0320 code is triggered when 2 successive erratic PIP pulses are detected.
Possible Causes: - Loose wires/connectors - Faulty Crank Position Sensors - Arcing secondary ignition components (coil, wires and plugs) - Low battery charge - Powertrain Control Module
Possible Solutions: - Resecure loose wire or connectors - If battery charge is low, recharge or replaced battery - Replaced crank position sensor - Replaced starter motor
Coil packs are replaced not repaired if found to be defective.
---DISTRIBUTORLESS IGNITION SYSTEMS
Starting in 1987, some models came with engines equipped with a Computer Controlled Coil Ignition (C3I) or Distributorless Ignition System (DIS).
Fig. 1: Triggering system used on the C3I fast start system
Fig. 2: Electrical schematic on C3I ignition system
Both DIS and C3I system consists of the coil pack, ignition module, crankshaft sensor, interrupter rings and ignition control module (ICM). All components are serviced as complete assemblies, although individual coils are available for Type 2 coil packs. Since the ICM controls the ignition timing, no timing adjustments are necessary or possible.
Fig. 3: Wiring schematic used on the C3I ignition system
Fig. 4: Notch effect on the output signal used on the crankshaft sensor
If the charging system is not putting out
the required voltage, is it the alternator or the regulator? Full
fielding the alternator to bypass the regulator should tell you if it is
working correctly. Or, take the alternator to a parts store and have
it bench tested. If the charging voltage goes up when the regulator is
bypassed, the problem is the regulator (or the engine computer in the
case of computer-regulated systems). If there is no change in output
voltage, the alternator is the culprit.
When the engine cranks normally but won't start, you need to check ignition, fuel and compression. Ignition is easy enough to check with a spark tester or by positioning a plug wire near a good ground. No spark? The most likely causes would be a failed ignition module, distributor pickup or crankshaft position (CKP) sensor.
A tool such as an Ignition System Simulator can speed the diagnosis by quickly telling you if the ignition module and coil are capable of producing a spark with a simulated timing input signal. If the simulated signal generates a spark, the problem is a bad distributor pickup or crankshaft position sensor. No spark would point to a bad module or coil. Measuring ignition coil primary and secondary resistance can rule out that component as the culprit.
I would be thinking that there is a good chance that you need to be checking out replacing the computer, if you aren't getting any communication with the proper scan tool then the computer isn't communicating with anything in the vehicle...... I would have guessed first off that the ignition control module might be bad but that is obviously part of the computer also, I would be looking in that direction.
Check voltage at coil. Check coil output (spark should be healthy even at 1/4" away from ground). If OK, then change module The only testing on module is with a special tool. Therefore if contacts are clean, that's all you can do with it!