Does an inline spark tester adequately show the quality of spark?

[hkeiner]

Can an "inline" spark tester be used to test whether there is a WEAK spark? I know that the inline tester can adquately show the existence or absence of a spark, but am not sure how well it can represent the quality of the spark by how bright the spark appears in the tester. I know that the testers that are NOT inline and instead have a clip to ground show the actual spark and so one can judge the quality of the spark by how bright it is. I just don't know if the inline types work the same way since the juice is also passing through a spark plug at the same time..

Also, since the gap is not adjustable on the inline type spark tester, can one assume that the gaps of the different brands/models are similar and appropriate for testing a 1996 Mercury 150hp outboard with electronic (non-distributor) ignition. The SN of the motor is OG397853?

Thanks for any input on this subject.

Hal

 

[WillyBWright]

Re: Does an inline spark tester adequately show the quality of spark?

If the spark will jump the gap of the sparkplug plus the tester, chances are very good that the quantity of spark is just fine for the sparkplug alone.

Another way to test for spark is with an inductive timing light. If it flashes, there's spark. If your motor has a black stator (1996 is about when they went to red stators), you might get good spark at low end but lose it at high end (or vice-versa). That's where water testing it with a timing light clamped to each individual lead on successive runs can isolate a bad coil, bad switchbox, or bad stator. Or even a bad sparkplug.

 

[JUSTINTIME]

Re: Does an inline spark tester adequately show the quality of spark?

it should be blue/white not orange

 

[rodbolt]

Re: Does an inline spark tester adequately show the quality of spark?

depends on the inline tester, some are adjustable out to about 11/16ths gap.
the reason for the various air gap specs when testing ign at cranking is due to the fact that in actual running combustion presures the electrical load increases.
as the load increases so does the voltage required to make an arc acrossed the electrodes.
as th firing voltage increases and electricity is lazy if there is a defect in the ign coil or secondary wiring eventually the arc will be to ground outside the plug gap.
I dont like the timing lamp method of spark testing. it can lead to erroneous results costing valuable testing time.
an example, F225. customer complaint, runs well starts easy but lacks power. Top RPM is down from 5700 to 4500.
one of the young tech´s tested it, spark on all 6 according to his inductive timing light and spraying fuel down the air intakes made no difference. a leak down test and spark test had revealed no issues.
his next step for reasons he could not explain as to inspect valve clearence.
at this point I intervened and stopped him.
a Kv test showed #6 plug had fouled with a firing voltage of about 2KV. more than enough to trigger his light but not near enough to spark the plug gap.
as the porcelian around the center electrode was contaminated and carbon is a fair conductor the electrical current was simply taking the path of least resistance. it was traveling from the center electrode down the insulator to the plug shell.
It will leave distinctive tracks ,normally, but the tech did not catch it.
about 3 1/2 hours was spent on a defective spark plug test.
about the only way to accurately find this problem was a Kv tester or an experienced eye.
my eyes are getting dim so I use the correct diagnostic tool.

 

[Texasmark]

Re: Does an inline spark tester adequately show the quality of spark?

Hey Rodbolt, that's one of my curiousities with surface gap plugs.

Put in new white ones, run for a few minutes and pull out a carbon track. Run it for years and the track is still there, but bigger, yet it runs smooth as silk.

Been heavily involved in high voltage and ignition type (pulsed) systems all of my professional life but fail to figure out how a really fast CDI (microseconds to 10's of microseconds) can fire the plug before the firing energy gets shortedout by the resistance of the carbon track.

We used to use a rule of thumb of .1" per kv (surface creep) which would give you 40 to 50 kv for .04 to .05" gap which I guess fits in there with the 45kv that my Merc Service manual says my '02 90 hp puts out; but that's surface creep across a non conducting surface....like a clean ceramic insulator. A carbon track is carbon and a conductor so I just don't get it.

You take a regular plug and the length of the insulator is humongous in comparison and there is no carbon track on it.

It (the manual) also says that it should jump a 7/16 gap which is a pretty good sized gap. Don't remember the conditions/tester/test method under which the number is valid.

Which brings on another point (boy this just goes on and on): We were talking, the other day, about not firing your engine with the plug wire off the plug due to unlimited (sorta) high voltage. Well, jumping a 7/16" gap at one atmosphere takes a pretty goodly amount of voltage (especially a fast rising voltage) which one would think would be adequate to overstreess sensitive trigger electronics.

Oh well. What do I know. I'm retired. I'm trying to forget what I used to have to know. d

Mark

 

[Plainsman]

Re: Does an inline spark tester adequately show the quality of spark?

I am interested in this as well. I have no idea what a kv is, but I do have both types of testers. So according to what I read in rodbolts post, the gap tester is far better that the enclosed type tester. Is that correct? And what is the correct setting, is 7/16 the "standard" setting? I can't find it in my merc manual.

 

[Dunaruna]

Re: Does an inline spark tester adequately show the quality of spark?

[colour=blue]kv = kilovolt

1 kilovolt is 1000 volts.

 

[hkeiner]

Re: Does an inline spark tester adequately show the quality of spark?

A Kv test showed #6 plug had fouled with a firing voltage of about 2KV. more than enough to trigger his light but not near enough to spark the plug gap.

I tested my 1996 150hp carbed Mercury outboard with both an inline spark tester and an adjustable spark tester and it shows a spark on all cylinders when cranking the motor with the starter (with all plugs removed and grounded). Rodbolt's comment seems to indicate that a more reliable way to confirm that the spark is OK at all engine speeds is to perform a "KV test."

I want to test the spark on my motor using the most reliable method to detect any deficient spark on a cylinder, even if it costs me a little more money for new testing equipment and/or a little more effort to learn how to test it correctly.

Can anyone expand on what the "KV test" is and what results distinguish a good vs bad test result. I guess that you need either a special meter (voltage peak meter?) or a regular voltmeter with an accessory. That is the extent of my knowledge at this point. I bought the Mercury shop manual for my motor and read the ignition section but the ignition troubleshooting section seems a bit complicated and I don't know for sure which steps are the "KV test."

Thanks