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Ignition Coil/Wire Resistance

  • Thread starter Thread starter fenderfreek
  • Start date Start date
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fenderfreek

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I seem to be getting a pretty weak spark on my 2/3 coil, but the 1/4 coil is sparking pretty strong. All plugs are NGK 9's gapped to .028. I checked the HT leads, expecting the 2/3 to come up very high but here's what I got instead -

2/3 HT wires, 35K Ohm(normal from what I can tell)
1/4 HT wires, 75K Ohm(very high?)

It's exactly opposite what I thought it should be, so I'm at a loss here - is the 2/3 coil just bad? :confused:
 
35K secondary resistance is right for stock coils, measured from spark plug cap to cap. Measure the primary resistance while you're at it, should be around 5 ohmns for stock coils.

Are you running stock wires & caps?? Are your plugs resistor type plugs?? They would have an "R" in the number.

If you haven't already, untwist the caps off each wire, (test the resistance of each cap while they're apart), trim the wires back 1/4" or so, then re-install the caps & see how that reads.

Even better, replace the stock caps with some NGK ones (call Z1 & they will hook you up...). Just don't use resistor plugs with NGK caps, too much resistance that way & the spark will be weak
 
cap resistance

cap resistance

What is the resistance of the spark plug caps supposed to be?
 
mbwjr12 said:
What is the resistance of the spark plug caps supposed to be?
Click to expand...

5K each. SO of the 35K, 10K is the caps.
The cap resistance goes up with age and usage, can go to almost infinite which then is no spark.

.
 
fenderfreek said:
I seem to be getting a pretty weak spark on my 2/3 coil, but the 1/4 coil is sparking pretty strong. All plugs are NGK 9's gapped to .028. I checked the HT leads, expecting the 2/3 to come up very high but here's what I got instead -

2/3 HT wires, 35K Ohm(normal from what I can tell)
1/4 HT wires, 75K Ohm(very high?)

It's exactly opposite what I thought it should be, so I'm at a loss here - is the 2/3 coil just bad? :confused:
Click to expand...

Describe what you see as "weak spark" and "Strong spark".

Yes, 75K is pretty high. Most likley due to one or both sparkplug caps failing. THose are only about $5 each to replace. But that doesnt seem to be the two you are having the spark problem on.

As stated before: also chack the resistance of the primary side of the coils.

Also maybe check voltage to the coils, although the conenctions to the 1/4 coil is right next to the 2/3 coil, so not much chance of a problem in the wiring. Maybe right at the connector on the coil....?

<< later note.
Oh, now I see you note about already having the coil relay mod. SO you should be familair with the power to the coils. >>>

.
 
Last edited:
Redman said:
Describe what you see as "weak spark" and "Strong spark".

Yes, 75K is pretty high. Most likley due to one or both sparkplug caps failing. THose are only about $5 each to replace. But that doesnt seem to be the two you are having the spark problem on.

As stated before: also chack the resistance of the primary side of the coils.

Also maybe check voltage to the coils, although the conenctions to the 1/4 coil is right next to the 2/3 coil, so not much chance of a problem in the wiring. Maybe right at the connector on the coil....?

<< later note.
Oh, now I see you note about already having the coil relay mod. SO you should be familair with the power to the coils. >>>

.
Click to expand...

The spark on 1/4 is a solid blue spark that goes straight from the center electrode to ground. On 2/3, it's small and purplish, and not consistent at all. I noticed it when I was using my colortune - the spark on those two was really sporadic, and I had to get the fuel mix pretty rich just to get any spark in those cylinders. I went ahead and got thenew boots from Z1 so we'll see how that goes.
 
fenderfreek said:
The spark on 1/4 is a solid blue spark that goes straight from the center electrode to ground. On 2/3, it's small and purplish, and not consistent at all. I noticed it when I was using my colortune - the spark on those two was really sporadic, and I had to get the fuel mix pretty rich just to get any spark in those cylinders. I went ahead and got thenew boots from Z1 so we'll see how that goes.
Click to expand...

Couldn't hurt to also remove the sig gen cover & inspect/clean the pick-up areas. Might be a little gunked up on 2/3 side?

However, I did notice a vast improvement in spark quality when I replaced the caps on my stock coils with NGK ones - hope that fixes it for ya...

Good luck,

Mike
 
Swap around caps and see if it makes a difference.
Check connections on the 2&3 coil.
Check resistance between the two leads on the coil in question and report findings.
 
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