Testing spark plugs

[Fab1]

Hi guys,there's a few ways to check if a spark plugs in good condition or not when diagnosing spark issues with any engine and one way is with the use of a simple multimeter.

Most sparkplugs have a resistor built in to them to suppress interference from other sources and will usually test at between 4,000-7,000ohms when in good condition.

In this example I have removed all six spark plugs out of my ute to check the condition of them.

I always number my spark plugs as I remove them so I keep track of what cylinder has an issue if any when doing a compression test,reading the sparkplugs etc.

Set your multimeter to 20k ohm range as shown.

Touch the probes to either end of the spark plugs as shown.

Look at the display of your multimeter,you should be reading around 4-7kohms.As you can see I have a reading of 3970 ohms which is great indicating the centre electrode is in good order.

Now keep the same setting in your multimeter but touch the probes like indicated.You are testing for a short to ground now,you should have no reading in the multimeter indicated by a 1.

As you can see there is no short between the centre electrode and to ground.

These tests should be performed when the spark plugs are hot and cold.

If the resistance on the first test tests to high for example 15kohms the plug is faulty,you want as little resistance as possible.

If the second test shows any resistance at all you have a plug shorting to ground I:e it will not spark at the electrode.Sometimes it can be caused by carbon buildup in between the electrode insulator and the spark plug body and a simple clean out will rectify it other times it can be carbon tracking or a cracked insulator causing the short.

I always test my sparkplugs,doesn't matter if it's my car,boat or power equipment and gap new ones even though they are suppose to be gapped at the factory and have come across some faulty brand new ones over the years.(Usually cracked insulators).

Thanks.

[bessell1955]

Thank you for this information. I have only shorted the plugs out and if there was a spark, then I thought all was well.

[The Incredible Hull]

Thats awesome info Fab, my motor is due for its winter service, I'll be following your method =)