Testing Spark Plugs Using An Ohmmeter

[cpurvis]

Grounding the plug and looking for spark is more of a verification that the ignition system is working..

There are a lot of pure garbage videos on youtube. In most cases, you have to already know what you're doing to be able recognize garbage when you see it.

 

[seattlepioneer]

Seattle. All the inline spark testers will show false positives in some cases. Also grounding the plug and seeing spark doesn't mean that the plug is firing under compression or in some cases the spark will jump from the center electrode to the side of the plug instead just jumping the gap even though it is narrower than the path the spark is taking will not fire under load.

Thanks for the additional comments.

My experience as a furnace repairman was that a part was MOST LIKELY to be bad when it was new, right out of the box.

Have you found new spark plugs that were no good, or does the manufacturer's inspection/quality control eliminate that?

 

[seattlepioneer]

<< All the inline spark testers will show false positives in some cases. >>


Heh, heh! Of course I bought one of these a couple of weeks ago....

But if they show a plug is no good, that test would be reliable?

 

[ILENGINE]

Thanks for the additional comments.

My experience as a furnace repairman was that a part was MOST LIKELY to be bad when it was new, right out of the box.

Have you found new spark plugs that were no good, or does the manufacturer's inspection/quality control eliminate that?

Had a 24 plug shop pack of J19LM that all failed within 10 minutes of first run after installation

 

[seattlepioneer]

Grounding the plug and looking for spark is more of a verification that the ignition system is working..

There are a lot of pure garbage videos on youtube. In most cases, you have to already know what you're doing to be able recognize garbage when you see it.

So you regard that as verifying that the high voltage spark is likely functioning, not that the spark plug is OK? Presumably an in line spark tester produces similar results? But neither method reliably tests the spark plug.

That appears to be consistent with B&S specifications that commonly specify routine replacement of the spark plug after so many hours of engine operation rather than trying to test the spark plug.

 

[Hammermechanicman]

Here is an example of 3 spark testers. First off none of these will tell you if the spark plug is bad or not. What they will tell you. First is the inline neon tester. It will tell you if the system is generating energy and is making it to ground somewhere. Just because it flashes doesn't mean the energy jumped the plug gap. A shorted internally or fouled plug can let the tester flash but plug may or may not be working properly. This type tester is especially good at finding failing coils on twin cylinder engines. Install one one each cylinder and if a coil is failing after runnibg for a while this type will show it.
The second one, the Briggs tester has a calibrated gap and is used without a spark plug. It will tell you if you have spark and if it has enough energy to run an engine. This is a good tester to check the basic condition of the system. If the spark can jump the gap it will run the engine.
The third one with adjustable gap can tell you how much relative energy the ignition can put out. None of these will tell you if the timing is off. There is also the 3 point spark test you can do with the adjustable tester but i have never neede to do it. Taking the plug out and laying against the block is NOT a good check of the plug or the ignition system.

 

[Hammermechanicman]

Had a 24 plug shop pack of J19LM that all failed within 10 minutes of first run after installation

Bummer there. How did they fail? internal short?

 

[Rivets]

We don’t call it a mistake, we call it a learning experience.

 

[ILENGINE]

Bummer there. How did they fail? internal short?

Appeared to fail open. Install plug, start engine, and within 3-10 engine would die. Check for fire and find none, replace plug and repeat. Spring tune up period so customer would return mower saying it just died. Multiple engines over a few week period.

 

[Hammermechanicman]

Appeared to fail open. Install plug, start engine, and within 3-10 engine would die. Check for fire and find none, replace plug and repeat. Spring tune up period so customer would return mower saying it just died. Multiple engines over a few week period.

I wonder if those were part of the ones that were the first batches out of Mexico. They had problems when they first opened the plant there.