How to Diagnose a Loss of Spark in Your Car Engine

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A very simple and inexpensive method to diagnose a loss of spark in your car engine.

Steps

1. 1
   Disable the fuel system by removing the fuel pump fuse or relay. you do not want to have your engine start while a wire is disconnected because fuel will still be added to the cylinder and not ignited.
2. 2
   Remove the spark plug wires one at a time and insert a small screw driver into the wire.(SEE WARNINGS) Be careful as you don’t want to get shocked with 60,000volts. Hold the wire so that the screw driver is 1/8” away from the engine. Have someone crank the engine and watch for a good white spark. If you have a good spark on all wires look for a problem with timing or something else.
3. 3
   Remove the distributor cap. Have someone crank the engine over with the distributor cap removed and observe if it is turning? That is if it has a distributor cap, some newer cars don’t have one. If the distributor is not turning then likely you have a broken timing belt or chain.
4. 4
   Turn the ignition key on but don't crank the engine. Locate the positive or power wire attached to the engine coil. Using a test light check for power. If this has power, then the wiring from the ignition switch is OK.
5. 5
   Locate the negative or ground wire attached to the engine coil. Using a test light check for power. This sounds strange however, one end on a good battery ground and the other on the negative wire attached to the engine coil. The test light will light up indicating power on the negative side of the coil with the key on and engine off.
6. 6
   Have someone crank the engine while watching the test light. If you observe the test light flickering when cranking the engine and you have no spark, either the coil wire is faulty of the coil is dead. Test these using an Ohm meter.# If no flickering or pulsating was observed then check continuity in all primary circuit wiring for opens. This is the negative wire back to it's source, the ignition module.
7. 7
   Check the pulse generator in the distributor if it has a distributor cap. Some newer cars don’t have one,and if it doesn’t then the ECM or computer sends signal via the crankshaft position sensor and the camshaft position sensor.
8. 8
   With the engine in non-running condition connect your A/C voltmeter to the pair of wires at the pulse generator and crank the engine. You are looking for an A/C signal that makes 4-6 volts of A/C. If this is observed then the ignition module is dead or has a bad ground. If no A/C signal is observed then you have a dead pulse generator in the distributor.
9. 9
   Know that if this part of the primary ignition tests OK then check wiring to ECM pinouts for opens. If wiring tests are OK. Suspect the ECM or computer as a last resort.

   
   

Warnings

• Be careful as you don’t want to get shocked with 60,000volts.
• Be careful when checking the leads for sparks with a screwdriver, doing it this way can cause very expensive damage on newer engines, it is best use a spare spark plug or a proper tester for this job.

Things You'll Need

• A 12 volt test light
• A volt/ohm multimeter
• A spark Plug tester

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