Testing for Spark
A common cause for a no-start engine problem is the lack of spark at the spark plugs so, when a thread is made describing such a problem, it is often necessary to describe the proper procedure to test for this issue. Therefore, I decided to make a thread that describes a basic yet effective method to check for spark:
1) Buy a spare spark plug and gap it properly (inexpensive $2-3).
2) Remove the plug wire from one spark plug and insert the spare plug into the end.
3) While firmly grounding the threads of the spare plug against a metallic portion of the valve cover, have a buddy crank the engine.
4) You should see bright white spark (with a faintly bluish tinge) rather than weak orange or deep blue spark at the tip of the plug.
5) Repeat for the remaining three spark plugs.
Outcomes and more troubleshooting
A) If all plugs have weak orange spark, then check whether the coil in the distributor is bad. Your service manual (see link in my signature) describes resistance measurements to test the coil or, alternatively, have an auto parts store (e.g., AutoZone) test it for you.
B) If all plugs lack spark, then do these steps in order:
-Check whether the CEL remains ON when the key is turned to ON(II). If so, pull the code(s) as detailed at the link in my signature. If a code for one of the distributor sensors (codes 4, 8, or 9) or the igniter/ICM (code 15) is retrieved, then the distributor subassembly or the igniter/ICM, respectively, may need to be replaced. Also check whether the wire (often a Yel/Grn wire) running between the igniter/ICM and the ECU has continuity.
-Check whether the important ground wire on the distributor housing is loose or corroded. If so, clean it thoroughly with steel wool and retighten.
-Check whether battery voltage is reaching the coil and igniter wire (often a Blk/Yel wire) in the distributor when the ignition key is turned to ON(II). If not, there may be a bad wire or a blown fuse in the under-hood fuse/relay box. A bad ignition switch is another possibility.
-Check whether the coil or igniter/ICM in the distributor is bad. Again, there are resistance tests for the coil, but you may have to take the igniter/ICM to an auto parts store (e.g., AutoZone) for testing.
-Check whether the timing belt snapped. This is most easily done by removing the oil filler cap and, while a buddy cranks the engine, by peering into the hole with a flashlight to look for evidence that the camshaft is turning (e.g. movement of the rocker arms). If the belt snapped (=no turning), install a new belt, tension it properly, and then compression test the cylinders. The latter step is essential as major engine damage often occurs when the timing belt snaps.
-In some cases, lack of spark is due to a bad ECU. This is usually only considered if all tests described above yield negative results.
If anyone would like to make any comments, corrections, or suggestions for improvement, please make a post in this thread.
Last edited by RonJ; 08-19-2009 at 10:13 AM.