1. Ignition System:
* Ignition Coil: This is a common point of failure. You'll need a multimeter to check for continuity and resistance (consult your car's repair manual for the specific values). A visual inspection for cracks or damage is also important. A bad coil will often not produce a spark at the spark plug wires.
* Ignition Module (or Control Unit): This is the "brains" of the ignition system, sending signals to the coil. Testing this requires more advanced diagnostic tools, often a scan tool capable of reading trouble codes. A faulty module may prevent the coil from firing.
* Ignition Switch: Check if the ignition switch is providing power to the ignition system. You can usually test this with a multimeter at the switch itself while someone turns the key.
* Wiring & Connections: Corrosion or loose connections in the ignition system wiring harness are frequent culprits. Inspect all wires and connectors between the ignition switch, coil, distributor (if equipped), and the computer. Look for any signs of damage, melting, or corrosion. Clean any corroded terminals.
* Distributor (if equipped): Older vehicles may use a distributor. Check the distributor cap and rotor for cracks, carbon tracking, or corrosion. Replace them if necessary. Check the distributor's pickup coil (if you're comfortable working with older ignition systems).
2. Crankshaft Position Sensor (CKP Sensor):
* The CKP sensor tells the computer the engine's rotational position. If it's faulty, the computer won't know when to fire the coil. This requires a multimeter and usually specific resistance readings from your repair manual.
3. Cam Position Sensor (CMP Sensor):
* Similar to the CKP sensor, a faulty CMP sensor can prevent the ignition system from firing. Requires a multimeter for testing.
4. Computer (PCM/ECM):
* A failing computer can cause numerous problems, including a no-spark condition. This is difficult to test at home and usually requires a scan tool to check for trouble codes.
5. Fuel Pump Relay:
* While it may seem counter-intuitive, a failed fuel pump relay can sometimes *indirectly* affect the ignition system. The computer may sense something is wrong and shut down the ignition to prevent damage.
Troubleshooting Steps:
1. Check for power at the coil: With the ignition on, use a multimeter to check for power at the coil's positive terminal. There should be battery voltage.
2. Check for a good ground at the coil: Ensure the coil is properly grounded.
3. Inspect the spark plug wires: Look for cracks or damage. Replace if necessary. Consider using a spark tester to check for spark at each wire.
4. Check for spark at the spark plugs: The easiest way to do this is to remove a spark plug, attach a spark plug wire to it, ground the metal body of the plug to the engine block, and have someone crank the engine. Look for a strong blue spark.
5. Check the fuses and relays: Inspect all fuses and relays related to the ignition system.
6. Consult a repair manual: A repair manual specific to your 1990 Chrysler New Yorker is invaluable. It will provide wiring diagrams, component locations, and testing procedures.
Important Considerations:
* Safety First: Disconnect the negative battery cable before working on any electrical components.
* Repair Manual: A factory service manual is essential for accurate testing procedures and component specifications. Chilton's or Haynes manuals are alternatives, but may not be as comprehensive.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to take your car to a qualified mechanic.
Without more specific information (e.g., does the engine crank? Are there any other symptoms?), this is the best general guidance. Providing more detail will allow for more focused troubleshooting.
