Spark Plug resistance

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  any help , info ,  advice , thoughts  on this greatly appreciated    

  I've never thought about this before   until recently ,  normally  change plugs in the charger once a year , maybe two , , unless a plug starts to miss fire , sooner !  then just put a new set . reguardless of milage or time being in the motor etc .    

     what should the resistance be  , between the top & bottom of the electrode  ,  is it the same deal as plug wires ,  the least resistance is better ??  is there a reading to show a good plug / bad  plug ?  

decided to put a multimeter  & check the ohm resistance of all my sets of used plugs ! ,  center electrode ,  !! ( one of them I wonder moments  )
they  are the  same  champion plugs ,   figuring the resistance would all be  with in a + & - percentage ,  but they all are way way different  ,   some old plugs with a 1000 miles on them  have less resistance , than  a new one out the box , while another  used plug may have way more resistance than a new one  , then the  next new plug  will have much much more resistance  than the next old  & soo on  , no pattern   ,   is there anything in this  , or  am I looking for something that is not there , all old plugs worked ok ! except a faulty one on a couple of occasions , reason I changed plugs !!
is there a way to tell if a plug is weak , because of too much resistance or too little    , no idea how or is that how  works , am I over thinking stuff again  

ive never dabbled in ohm readings of a plug ,  as ive just  read plugs in normal way  over the years , & or pulled off a lead to a suspect cylinder  , or checked internal fault with a continuity tester etc  ,  when in doubt , put a new set of plugs in  

   
soo to sum it up !!!   does it matter  how much  or how little the resistance is  , even in 2 new boxes of four , champion plugs , the  resistance  varies ,   soo much  

[green69rt]

I ran this down.  I'm not sure if it's a complete answer but maybe a start.

http://forums.nasioc.com/forums/showthread.php?t=1146782

[tan top]

I ran this down.  I'm not sure if it's a complete answer but maybe a start.

http://forums.nasioc.com/forums/showthread.php?t=1146782

   interesting     


  thanks  for  posting  ,   greatly appreciated 

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  just for reference  , to show everyone what i'm talking about  , going to test all plugs  for ohm readings again ,  & the set that's in the motor now  ,  & post results here      ,   maybe it makes no difference ! more resistance , weaker spark ! may be it does  , more than likely i'm thinking about & doing stuff , I don't really need to    

[MoParJW]

From the NGK website:

''FAQs - Spark Plugs

Q: When should I use a resistor spark plug?

A: NGK "R" or resistor spark plugs use a 5k ohm ceramic resistor in the spark plug to suppress ignition noise generated during sparking.

NGK strongly recommends using resistor spark plugs in any vehicle that uses on-board computer systems to monitor or control engine performance. This is because resistor spark plugs reduce electromagnetic interference with on-board electronics.

They are also recommended on any vehicle that has other on-board electronic systems such as engine-management computers, two-way radios, GPS systems, depth finders or whenever recommended by the manufacturer.

In fact, using a non-resistor plug in certain applications can actually cause the engine to suffer undesirable side effects such as an erratic idle, high-rpm misfire, engine run-on, power drop off at certain rpm levels and abnormal combustion.''

I looked into this recently as I was running resistor plugs with (low) resistance wires, trying to find out if it would make a difference.

I checked my new NGK plugs, they were all pretty close to 5K ohm, the old Autolites that came out had a resistance ranging from 4K - 7K ohm.

According to the '68 Service manual, Chrysler used non-resistor plugs and resistor wires, if I understand correctly.
It says maximum resistance of the plug wires should be 30K ohm, and that is on a points type ignition... so that makes me think a couple of 1000 ohms more or less shouldn't really make a difference?  

[tan top]

  thank you  for the reply & info , MJW !!    greatly appreciated      



no where on any plug manufactures site , that ive found , have they listed ohm resistance between   A & B   showing a good plug or a bad plug ,

yet found something about it on a aviation web site   , for piston engined  aircraft

http://www.csobeech.com/spark-on.html this shows ohm readings  ,    no biggie finding out this info , just curious  

[b5blue]

  Well now you have me thinking.....   Soon I'll be doing likewise and post what I find.    I just bought a plug cleaner do-hickey from Harbor Freight that runs off the compressor and was going to clean all my extra plugs anyway.   

[MoParJW]

That's interesting, and confusing  
It makes what the FSM says about plug wires being ok under 30k ohm sound crazy to me.

Anyway when I get the car out in spring, I'm going to install the same type of sparkplugs, but without resistors, see if I can notice a difference.