Spark Plug Wire Resistance?

[flower_king001]

Check OHM on spark plug wires

one side reading 4.5 and the other 5.2
4.5

This is checking from one end of the wire to the cap.

What is and acceptable range/limit?

Thanks

[wirespokes]

5K is the norm for electronic ignitions. You're in the ballpark - it's when resistance goes up to seven, eight, ten K you know there's something to fix. The resistance should all be in the cap - 5K. The plugs should be non resistor - you definitely don't want resistor caps AND resistor plugs.

[Kiwi_Roy]

I insist on copper wire for the plug leads, that carbon core stuff is crap IMHO
As spokes says resistor caps or plugs not both.
My EV came with resistor caps and resistor leads.

I assume the resistance was was 4.5k and 5.2k I would think that was acceptable
If you have an ignition with two coils you can measure from the plug cap to chassis, this checks the cap, leads and coil in one fell swoop
Doesn't work with a distributor of course (spark gap inside)

[Tom H]

5K is the norm for electronic ignitions. You're in the ballpark - it's when resistance goes up to seven, eight, ten K you know there's something to fix. The resistance should all be in the cap - 5K. The plugs should be non resistor - you definitely don't want resistor caps AND resistor plugs.

My EVT specs resistor plugs and came stock with resistor caps. Odd, but that is what the factory installed.

Standard plug wire without caps, I have heard will be about 1ohm per foot. I'm sure this can vary.

Tom

[Old Jock]

5K is the norm for electronic ignitions. You're in the ballpark - it's when resistance goes up to seven, eight, ten K you know there's something to fix. The resistance should all be in the cap - 5K. The plugs should be non resistor - you definitely don't want resistor caps AND resistor plugs.

Nailed it!!

I am also not a fan of the carbon/graphite core leads but put a set into my LM 1000 when I diidn't know any better and they've been in about 20 years now and still function fine. No point in changing them out if they work

[Tom H]

I had a 26 year old standard coil wire on my Eldo. Has been running fine. I decided to change my plug wires since they were getting old and I didn't realize 20 year ago that I had used suppressor wires for the plugs. This is a picture of a NGK 5ohm cap:





This is the 26 year old coil wire:




I think the wire may have built up a bit of resistance?

Tom

[wirespokes]

One of my Guzzis came to me with both resistor caps and plugs, but the bike was 30 years old at the time so who knows how that happened. Just one of the little details needing correction.

The specification is for copper wire, but the other stuff will work. I very much prefer copper wire - we don't need suppression wire on our bikes and the copper is a much better conductor. What that means is a hotter spark which equates to better efficiency and more power. More than 5K ohms isn't needed and only reduces the spark power. I don't trust resistor plugs so recommend tossing them for the non resistor variety and keeping the 5K ohm caps.

Copper core wire  lasts forever - well, almost - until the insulation breaks down. When they get hard and brittle, they're way gone!

Many years ago I didn't see any reason for resistor caps on my R90/6 so ran without them. It ran fine, but supposedly some resistance helps deliver a hotter spark - maybe something to do with creating a resonance? Electronics can be more complex than it seems sometimes. Points ignitions should have 1K ohm caps.

[Gappy]

5K is the norm for electronic ignitions. You're in the ballpark - it's when resistance goes up to seven, eight, ten K you know there's something to fix. The resistance should all be in the cap - 5K. The plugs should be non resistor - you definitely don't want resistor caps AND resistor plugs.

.

What possible problems could arise from using both resistor plugs and caps?

[Rough Edge racing]

.

What possible problems could arise from using both resistor plugs and caps?

 If you have a car/truck made in the last 50 years it originaly had both resistence plugs and wires.. Bikes are generally considered high performance so the least resistence that will do the job is usually what's done.. Some electronics may be ok with 500 ohms resistence, some may need 5K...

[Wayne Orwig]

What possible problems could arise from using both resistor plugs and caps?

Probably none.

More resistance means a slightly lower spark current. That means the spark will last a bit longer. So maybe there is an advantage to more resistance in that respect.
Less spark current means the shape of the spark plug electrodes will hold up longer. And the gap will be more stable over the miles and miles. So maybe there is an advantage to more resistance in that respect.
In the case of electronic ignition, the RFI would be reduced. Less likely to mess with the electronics. So maybe an advantage there.

Mine came from the factory with 5k caps, and BPR6ES plugs. Never had an issue.
 

[MGrego]

My '04 EV also came with resistor caps and plugs.  Belt and suspenders from the factory I suppose !

Perhaps a good replacement for the stock leads and caps on the EV :

https://www.euromotoelectrics.com/Moto-Guzzi-Spark-Plug-Wire-Set-Silicone-30-inch-p/bmw-wsr30.htm