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Check by moving the spark plug, then wire (or COP), then Fuel injector (to see if the code changes to another cylinder, I.E. 301,303,303) then check with compression/leak down test…
-Karl
-i only have a code reader ,and tools ! i cleared the check engine light , o you mean put spark plug in other cylinders ok ,,,i see to see if spark plug is the problem, ican change wire ,and fuel injector ,after clearing CEL it has not come on , yet runs a little rough ,,alittle,
Neon’s are very picky on plugs and are known for coil issues.
You might need to pick up an actual spark tester to stress the coil and ensure it is not internally shorting. When you test for spark at number 4 also test number 2, since your design is a waste spark method the coil actually fires cylinders 2 and 4 simultaneously, if 2 fires and 4 does not it usually indicates a shorted coil. If you do not have spark going to the number 4 cylinder, get a test light and check for power on the dark green wire with an orange stripe (this should be good as your other plugs are firing), next take your test light clip and place it on the batteries positive terminal (you are now testing for grounds). Probe the dark blue with tan wire while the engine is running the light should be flashing, then test the black with a grey stripe wire and it also should be flashing.
Most likely you have a failed coil, the design uses very little insulating resin and neon coils are known to get very hot and the resin breaks down allowing the coil to “cheat” and fire internally instead of through the plug wire.
If you have good spark on number 4 you will want to test the injector. Unplug the number 4 injector and turn the key to on, test for power on the dark green wire with an orange stripe, you should have power when ever the key is on or the engine is running. If you do, set your test light up for checking grounds again (clip on battery positive) and start the engine with the injector still disconnected (if you have it connected the test light will ground the injector and hold it open, you don’t want that) and probe the light blue with brown wire, it should be flashing.
Start with the basics as many have suggested. I like to start with a power balance test when looking for misfires. A video on how to do a power balance and additional information on solving performance problems can be found in this article I wrote.
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted on your progress.
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