1. Check the Basics (Always start here!):
* Battery: Is the battery fully charged and the terminals clean and tight? A weak battery can cause intermittent or no spark. Test the voltage directly at the battery terminals.
* Battery Cables: Inspect the positive and negative battery cables for corrosion, loose connections, or breaks. Clean or replace as needed.
* Fuses and Relays: Check all fuses related to the ignition system (look in your owner's manual for locations and ratings). Also, inspect any relays related to ignition or the ignition module. Some Ford trucks of this era used several relays.
2. Ignition System Components:
* Ignition Coil: A faulty coil won't produce the high voltage needed for spark. You can have a mechanic or auto parts store test it for proper resistance. Visually inspect it for cracks or damage.
* Ignition Module (or Electronic Ignition Control Unit - EICU): This is a common failure point in these older Ford trucks. A faulty module prevents the coil from firing. Again, testing is best left to a professional or using an appropriate meter.
* Distributor Cap and Rotor: Inspect the distributor cap for cracks, carbon tracking (black marks), or corrosion. The rotor should spin freely and show no signs of wear or damage. Replace if necessary – these are inexpensive parts.
* Ignition Wires (Spark Plug Wires): Check the wires for cracks, fraying, or loose connections at both the distributor cap and the spark plugs. A cracked or damaged wire will prevent spark. A simple visual inspection is usually sufficient, but testing with a spark tester can verify.
* Spark Plugs: While unlikely to be the *sole* cause of no spark (as you'd get intermittent sparking if they were bad), worn or fouled spark plugs can prevent a strong spark. Inspect them and replace if necessary.
3. Crankshaft Position Sensor (CKP Sensor):
* The CKP sensor tells the ignition module when to fire the spark. A faulty CKP sensor can prevent spark altogether. This is a crucial part to check, especially since you're getting fuel. You'll likely need a multimeter or a scan tool to diagnose this.
4. Wiring and Connections:
* Trace the wiring from the ignition switch to the coil, the distributor, and other ignition components. Look for broken wires, corrosion, or loose connections.
5. Testing (If you have the tools):
* Spark Tester: This is the best way to definitively determine if the coil is producing spark.
* Multimeter: Use a multimeter to check the voltage at the coil, and to test the continuity and resistance of various ignition components.
Important Considerations:
* Professional Diagnosis: If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic. Improper diagnosis and repair can lead to further damage.
* Year-Specific Information: A 1990 Ford 5.8L truck's ignition system is complex. Look up a wiring diagram and repair manual specific to your year and model. These diagrams are usually available online or at auto parts stores.
By systematically checking these areas, you should be able to isolate the cause of the no-spark condition. Remember safety first – disconnect the negative battery terminal before working on any electrical components.
