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Weak spark.Trying to test my coils

  • Thread starter Thread starter antlese
  • Start date Start date
A

antlese

Guest
Hi Guys,
I am getting a spark on each of the spark plugs on my 1984 GS550L. But the sparks look weak to me. I'm not entirely sure if the spark is healthy or not, so I thought I would get myself a multimeter and test my coils.

I removed the primary wires from each coil and I'm getting around 3.7 ohms between the "+" and "-" contacts. I understand that this is within normal range.

When I try testing the resistance on the secondary (plug wire), I do not get a reading. I have tried each coil and each spark plug cap. But I do not get a reading. I have selected the various resistance settings on the multimeter as well. Still nothing.

I am not sure if the metal probe on the tester is making contact with the metal inside the spark plug cap. Can I remove the spark plug cap, or can I somehow modify the multimeter probe to extend further into the cap so I can get a reading?

Any thoughts or comments would be appreciated. :)

Antlese
 
Remove the plug caps and measure wire to wire on each coil- should be about 12 kohms. Measuring over caps is tricky as corrosion prevents meter probes from making good contact, but it can be done if you wiggle probes around in caps (assuming they fit into caps far enough)
 
The caps can be removed from the wire, like tom203 says. Standard advice is to cut off about 1/4" of wire and then twist the caps back on. This ensures a good connection between the cap and wire.

Also, the insides of the plug caps can be removed with a flathead screwdriver. Inside there will be the brass piece which clips onto the spark plug and a resistor. The caps for 2 & 3 will also have a spring inside because they're longer. Clean these up as best you can with contact cleaner, vinegar, or your solvent of choice.

When I did this on mine recently, I found that the resistors were pretty well fried: the contacts had disintegrated and one no longer conducted electricity, so the spark actually jumped over the resistor and left a carbon trail over the length of it. I replaced the resistors with cut-off screw threads of identical length. If you do the same, it would be a good idea to replace your spark plugs with ones that have resistors in them. (On my bike, that would be BR8ES instead of B8ES.) Having some resistance in the high-voltage circuit is good, it prevents nearby electronics from going all wonky. If you carry a cell phone or any other electronic device, you have a good reason to limit the RF interference generated by the engine.

Or you could throw money at the problem and buy new spark plug caps. YMMV.

If you do all this and _still_ get infinite resistance between caps, you probably have a break in the wire somewhere or (less likely) the coil. It may still function (generate spark), but not quite as well as it could.
 
eil said:
The caps can be removed from the wire, like tom203 says. Standard advice is to cut off about 1/4" of wire and then twist the caps back on. This ensures a good connection between the cap and wire.

Also, the insides of the plug caps can be removed with a flathead screwdriver. Inside there will be the brass piece which clips onto the spark plug and a resistor. The caps for 2 & 3 will also have a spring inside because they're longer. Clean these up as best you can with contact cleaner, vinegar, or your solvent of choice.

When I did this on mine recently, I found that the resistors were pretty well fried: the contacts had disintegrated and one no longer conducted electricity, so the spark actually jumped over the resistor and left a carbon trail over the length of it. I replaced the resistors with cut-off screw threads of identical length. If you do the same, it would be a good idea to replace your spark plugs with ones that have resistors in them. (On my bike, that would be BR8ES instead of B8ES.) Having some resistance in the high-voltage circuit is good, it prevents nearby electronics from going all wonky. If you carry a cell phone or any other electronic device, you have a good reason to limit the RF interference generated by the engine.

Or you could throw money at the problem and buy new spark plug caps. YMMV.

If you do all this and _still_ get infinite resistance between caps, you probably have a break in the wire somewhere or (less likely) the coil. It may still function (generate spark), but not quite as well as it could.
Click to expand...


Excellent! Thanks guys. I will try removing the plug caps from the wires and restesting them. If I get a reading that is within an acceptable range I will clean the contacts up that are inside the caps.

Antlese
 
Seems I was testing the secondary wires incorrectly. I had one multimeter probe on the primary contact, and the other in the spark plug cap. Even after removing the cap from the wire I still did not get a reading on my multimeter. LOL.

So did a little more reading on here and discovered that I need to put a probe in each of the caps at the same time. Doh!

So I put my multimeter on 200K ohms. Put a probe in spark plug cap 1 and the other probe in cap 4. The readings ranged quite a bit but seemed to settle around 36 to 37. Same with the readings on caps 2 and 3.

I took both readings with the caps still attached to the secondary wires.
So I'm glad that I'm getting a reading now, but I'm not sure if the numbers are ok.

Thoughts?

Antlese
 
antlese;1887894...... So I put my multimeter on 200K ohms. Put a probe in spark plug cap 1 and the other probe in cap 4. The readings ranged quite a bit but seemed to settle around 36 to 37. Same with the readings on caps 2 and 3. I took both readings with the caps still attached to the secondary wires. Thoughts? Antlese[/QUOTE said:
Thoughts ? it's hot here! 36 to 37 kohms is slighty higher than 32 kohms which I measured on a few stock sets cap to cap. New ngk plug caps (maybe $5 each) could drop you down into 25 kohm range.
Click to expand...
 
1981 gs650g

1981 gs650g

Hi, testing coils, HT to HT caps removed, reading 12.65 on the 20k scale, book says 30-35k with the caps on, seems a big difference, can you guys shed some light ? Thanks.
 
Yes, with caps off, 12.65 kohm is fine; caps on, you might read anywhere from 24 to 34 kohm depending on cap brand.
What problem are you having?
 
Last edited:
1981 gs650g

1981 gs650g

No problem, as such, just starting a frame off resto & establishing some starting points. Bike is fitted with DR8ES-L plugs, book says D8EA, the 'R' value of the plug caps are -zero-9.56-14.25-4.8, looks like new plugs & caps, what should stock be ?
 
1981 gs650

1981 gs650

What are the correct NGK plug covers ? NGK don't seem to have any way of identifying the bike.
 
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