Dead Sparkplug?

[Tagged]

I’m splitting this question out of my main thread because it’s a problem I’ve not seen written about, and may deserve special attention.

My main rebuild thread is here: https://forums.iboats.com/forum/eng...ds/10527841-tagged’s-140-johnson-resurrection

After replacing the #1 ignition coil, I still didn’t have spark. Using a gap-style spark tester, I determined that I had no spark, zero, if I connected the tester between the HT lead and the head of the spark plug, where the HT lead would normally connect.

But it if I connect the tester between the HT lead and the base of the spark plug, where you put a wrench on the plug, it would jump a spark across a 1/2” gap.

Does that mean mean the plug is bad? I’ve never heard of that happening. I didn’t have a plug wrench with me to check if it was simply fouled.

Ideas?

 

[jakedaawg]

Not valid test. Open air gap checker is placed in place of plug. It needs one end at ground. There can be only one load (gap) in the circuit.

 

[Tagged]

Ok, maybe I’ve been using the tool wrong.

But it all three other cylinders will throw a half inch spark when I connect the tool between the HT lead and the top of the plug.

 

[jakedaawg]

You may have s weak coil or bad wire but still not proper way to use tester...

I have seen many bad plugs right out of the box....

 

[boobie]

Maybe you have 3 bad plugs ??

 

[jimmbo]

Could be several weak areas(coil, wires, sensor/trigger, plug, insulators,) that combined, keep the spark from happening

 

[oldboat1]

This open air adjustable tester (cheap):

 

[oldboat1]

Suggest removing all plugs — attach clip to a solid ground at the powerhead.

Testing ignition output. If you get a half inch spark with the tester, you will jump the .030 plug gap.

The plug base is grounded to the powerhead — terminal is not. To test plugs, look for continuity from the terminal to the center electrode. I’ve found NOS plugs with corrosion under the terminal (screw off the terminal nut and clean up the stud underneath, then test again).

 

[Scott Danforth]

did you drop the plug?

 

[Chinewalker]

Swap the plug to a different plug wire and retest. If issue follows the plug, then there's your issue.

 

[interalian]

Swap the plug to a different plug wire and retest. If issue follows the plug, then there's your issue.

^^This

 

[Tagged]

Answering the questions from above,

yes that’s the spark tester I’m using. Yes, I’m using it wrong. Yes, I probably still have a bad/weak/old coil or two. No, I didn’t drop the plug, but who knows what the previous owner did.

Thanks all all for the advice, sounds like the unusual behavior was caused by a batd test procedure introducing too many variables, and the test results need to be ignored.

Thanks everyone!