Testing Spark Plugs Using An Ohmmeter

[seattlepioneer]

Here's a You Tube video showing methods for testing spark plugs with an ohmmeter.

Comments are invited.

 

[Rivets]

90% of people don’t own a VOM or know how to use it, so we are talking about 10% of people could benefit. Of that 10%, 9% are technicians who know that it is faster, easier and cheaper to just replace the plug. Looks like a guy looking for U-tube advertising dollars.

 

[seattlepioneer]

90% of people don’t own a VOM or know how to use it, so we are talking about 10% of people could benefit. Of that 10%, 9% are technicians who know that it is faster, easier and cheaper to just replace the plug. Looks like a guy looking for U-tube advertising dollars.

Ummm. So your method is guessing and supposing what the problem might be, preferring that to testing your theory and knowing for sure?

-Could be a bad spark plug --- replace it.

-Could be a dirty carb ----replace it.

- Could be a bad coil ----replace it.

And so on.

In the furnace repair bus I was part of, this kind of guessing was the mark of a poor repairman.

The good repairman had a extensive skills in how to test possibly defective parts, and tended to work his way through a series of tests until he was confident he had identified the actual problem.

I had quite a bit of experience with repairmen of the poor type because I often followed along behind them when their repairs didn't actually fix the problem, which recurred.

I do note, however, that B&S maintenance requirements often specify replacing spark plugs after a few hundred hours of machine operation as a matter of routine maintenance. I suppose that would justify routine replacement of spark plugs, but you still aren't really going to know if the plug was the problem or whether you should look further.

 

[Hammermechanicman]

Using an ohmmeter to test a spark plug is pretty much useless. When i worked at a small airport one summer i tested spark plugs. After the plugs were cleaned you put them in a machine that pressurized the plug to a few hundred PSi then you turn up the voltage and measure how much voltage it takes to fire the plug and checked the plug doesn't arc across the insulator.

 

[Rivets]

If you would read my post you would see I said replace the plug. Never said anything about any other parts. A good repair man knows how to read and understand the printed word. I guess you think I’m a pretty poor repairman and you are entitled to that opinion, but I disagree.

 

[4getgto]

I never ever ever put a ohm meter on a plug for checking condition of a plug. His video talked a lot about resistive spark plugs that's all well and good. But if it's just a cheapo mower plug there isn't much to check.
I always looked at the condition of the spark and went from there...

 

[seattlepioneer]

If you would read my post you would see I said replace the plug. Never said anything about any other parts. A good repair man knows how to read and understand the printed word. I guess you think I’m a pretty poor repairman and you are entitled to that opinion, but I disagree.

Simply replacing the spark plug isn't going to tell you whether it was the problem. That would be especially true for intermittent problems, which as a furnace repairman I often found the hardest to diagnose.

Especially with intermittent problems that I couldn't diagnose definitively, I sometimes found the best thing I could do was to do all scheduled or routine maintenance and perhaps replacing any parts that appeared to be worn or marginal. That might or might not solve the complained of problem. If the problem recurred, at least I could be pretty sure that it wasn't a matter of neglected maintenance.

<< I guess you think I’m a pretty poor repairman and you are entitled to that opinion, but I disagree.>>


Not at all. But I am interested in why you might that you prefer to replace a plug rather than try to identify whether it is the actual cause of a problem. Your stated reason for that was that you didn't find it worth while to find out. Perhaps that's defensible, but it doesn't appear to be a high standard.

 

[seattlepioneer]

Using an ohmmeter to test a spark plug is pretty much useless. When i worked at a small airport one summer i tested spark plugs. After the plugs were cleaned you put them in a machine that pressurized the plug to a few hundred PSi then you turn up the voltage and measure how much voltage it takes to fire the plug and checked the plug doesn't arc across the insulator.

What was the reason for doing an elaborate test rather than simply replacing the plugs with new ones? Under what circumstances would plugs be subjected to this kind of test -----as a matter of routine or when diagnosing a problem? Were new plugs tested in this way?

I'm reminded of the ETOPS standard of equipment standards for aircraft venturing over oceans: the high standards were jokingly referred to as Engines Turn Or Passengers Swim ---ETOPS!

 

[Rivets]

If you have to ask that question, you have never wo in the small engine industry. You are comparing a small engine to an HVAC system, which is like comparing males to females. My couple of years of experience have told me that it is cheaper to replace the plug when ever it may be part of the problem. Secondly, have you ever tested a part good only to have it fail a short time later. Labor rate around here is $80/hr, do you want me to get out my VOM and spend the time testing the plug, instead of just replacing a $3.50 part in two minutes.

 

[Hammermechanicman]

You can't look at a spark plug and tell if it is good or not. You need special equipment to test a spark plug. For $2 it is more expedient for a shop to replace a plug and see is that solves a spark issue rather than looking for a high tension spark plug tester. Some of us buffons running small engine shops may have some skills other than mowers. I serviced printing equipment for 40 years. Some of it multi million dollar systems with some single repair parts costing thousands of dollars. You better be able to troubleshoot logically or else look for another job

when aircraft were in for scheduled maint the plugs were removed, cleaned and tested. If they failed they wefe replaced. Some radial engines have 36 cylinders with two plugs per cylinder and 2 or 4 engines. With 2 engines that is 144 plugs and at close to $10 a plug aircraft owners don't want to drop an extra $1500 for plugs. Yes we tested and documented new plugs.