1. Wiring and Connections:
* Ignition Switch: A faulty ignition switch won't send power to the rest of the system. Check for power at the switch in the "run" and "start" positions. A wiring diagram will be helpful here.
* Power to the HEI Module: The HEI module needs power and a good ground. Trace the wires to the module and verify power and ground are present using a multimeter. Look for corrosion or broken wires.
* Wires to the Coil: Inspect the wires between the HEI module and the coil for breaks, shorts, or poor connections. A simple visual inspection and wiggle test can help identify these.
* Grounds: A poor ground can cause all sorts of electrical gremlins. Clean the ground connections at the engine block and chassis. Make sure the ground strap from the engine to the chassis is in good condition.
2. Crankshaft Position Sensor (CKP Sensor): The CKP sensor (if your '85 uses one; some did, some didn't depending on the exact setup) tells the HEI module when to fire the coil. A faulty CKP sensor won't generate the signal needed for spark. This is less likely if the module checked out okay, but worth checking. It's usually located near the crankshaft damper.
3. HEI Module (Again): Even though it was "checked," it's possible the test wasn't comprehensive enough. A more rigorous bench test (or a replacement) might reveal an intermittent failure. Also, ensure the module is correctly seated.
4. Ignition Control Module (ECM): On some fuel-injected systems, the ECM plays a role in controlling the ignition timing and spark. While less likely to be the *sole* cause of a complete no-spark condition, a faulty ECM could prevent spark. This requires more advanced diagnostics.
5. Distributor:
* Cap and Rotor: Check for cracks, carbon tracking, or excessive wear on the distributor cap and rotor. Even a minor issue here can prevent spark.
* Distributor Shaft: Ensure the distributor shaft isn't worn or binding. A worn shaft can disrupt the timing and prevent proper operation.
* Distributor Alignment: Make sure the distributor is properly aligned. Even a slight misalignment can interfere with spark generation.
Troubleshooting Steps:
1. Visual Inspection: Carefully examine all the wiring, connections, and components mentioned above.
2. Multimeter Testing: Use a multimeter to check for voltage and ground at critical points in the ignition system. Refer to a wiring diagram for your specific car.
3. Test for Spark at the Coil: Disconnect the wire from the coil to the distributor cap, and hold the end of the wire about 1/4 inch from a good ground. Have someone crank the engine. You should see a strong spark. If there's no spark here, the problem is before the coil. If there is spark here, the issue is in the distributor cap, rotor, or wiring to the plugs.
4. Check for Spark at the Spark Plug: Disconnect a spark plug wire, attach a spark plug, ground the plug, and crank the engine. If you don't see a spark here, the problem is in the distributor, wiring, or spark plug itself.
Important Notes:
* Wiring Diagram: Obtaining a wiring diagram specific to your '85 Camaro Z28 305 TBI is essential for accurate testing. You can often find these online (Haynes and Chilton manuals are good sources) or at a local auto parts store.
* Safety: Disconnect the negative battery terminal before working on any electrical components.
By systematically checking these points, you should be able to narrow down the source of the no-spark problem. If you're not comfortable working with automotive electrical systems, it's best to seek professional help from a mechanic.
