One cylinder not firing

[Tyler]

All stock D-jet motor, normally runs perfectly. Fired it up today and noticed a lumpy idle. Pulled the plug leads one at a time until I found the one that did not change the idle. Its got a spark, at least at the distributor. How can I check if the plug is dead or if the injector is not firing? What else should I look for?

Many thanks in advance.

 

[x_atlas0]

You could pull the plug, crank the engine, and smell for gas from the hole, for the injector test. The plug should be a visual confirmation sort of deal. I am a bit unclear, though as to if you checked the plug wire. I'd check the plug itself and the injector after the wire passes.

 

[Honolulu]

to check plug wire

remove wire from plug
remove plug from cylinder head
insert plug into plug lead connector
have assistant hold plug against head
crank engine

At this time, if the assistant screams in pain, you'll know that voltage is passing through the wire, through arm, and grounding to the engine or car where your assistant is leaning against it.

Alternatively, if assistant is astute enough not to receive the jolt, the plug will spark.

Either way, you will have proved the spark plug lead is okay.

NEXT TEST. One (or more) wires may be crossfiring, that is, the spark in one wire jumping through poor insulation to another wire. To check, separate all the wires, park in the dark, observe wires while running. You may see a spark where none should be, or you can hear it "tic-tic-tic" shorting each time that wire carries a spark. Replace offending wire and all should be better.