Coil Relay Mod/Spark Question

[Guest]

Hey,
I've been having issues with my bike running properly so I decided to use a tool to check for spark. On the one coil the spark is constant, on the other coil the spark is intermittent and inconsistent.

I have a new Dyna S, both are new OEM replacement coils, wires and caps, and the plugs are new.

I checked the voltage at the coils and was only getting 8v with 12v in the battery. I understand the coil relay mod is designed to fix this exact issue. So I followed the instructions to the coil relay mod, but after connecting everything up, I am still only getting 8v to the coils.
I checked the voltage going into the relay and it will pull battery voltage through until I connect the O/W wire. Once that's connected (while key is on and killswitch set to run) the voltage immediately drops to 8v.

Something obviously isn't quite right. Any ideas?

[salty_monk]

Is the battery strong? Where are you checking voltage? If you are using O/W as the trigger for the relay like I did then you will continue to get 8v on those but you'll get 12v at pin 87 which is basically a straight pass through from the battery once the trigger activates the relay.
If 87 is reading 8v then you have something else going on... either something is sucking all the life out of the battery or it's a bad battery or your wiring is wrong!

Have you tried checking pin 87 when the bike is running?

Dan

[GS1100G]

You should also check the grounding.
I discovered that the wire from the negative pole on the battery to frame were bad, and changed that.

Then there seems to be a bad connection from frame to engine on my bike, but a wire from the same pole to the engine block fixed that problem.

Just remember that you also need a good earthing to make a complete circuit.

[almarconi]

With that much voltage drop something is definitely amiss in your electrical system. With a fully charged battery, I would want to see 12.8 volts at the battery and ideally the same voltage at the coils. It's pretty common to see about a 1 voltage loss to the coils, even with 11.8 volts at the coils the bike should start. Before attempting the relay mod I would want to find out what is drawing that much voltage from the system. Start by cleaning your connections and make sure all your grounds are clean and tight.

Have you gone through the stator papers and checked the electrical components?

[cp___32]

Yeah the battery is fine. Like most of the electrical components on the bike it's new. It was reading in the 12's but the cranking slowed after a little while and I've taken it home to charge it again.
I have a couple of different relays, one has an 87 and 87a, one being N/O and one being N/C and before the O/W wire is connected I would get battery voltage coming out, but as soon as the O/W was connected it would immediately drop to 8.
I put a new ground on the frame just ahead of where the battery box mounts under the tank. I have not yet looked at the negative battery terminal ground but I will check that.
The bike did run prior to the mod, but after the mod it only ran for about 10 seconds and ran substantially worse than it did with factory wiring before it died and I haven't been able to get it running since.
It was my understanding that not having full voltage at the coils without the relay mod was a common issue, so when I saw that I was getting 8, I assumed it was attributed to the age and possible condition of the wires and loss due to the numerous connections, plugs, and other wiring components.
The coils are grounded via the two mounting bolts that go through the frame?
Does the issue I'm having with the spark not being consistent on only one of the new coils sound like it's strictly a voltage issue? I know I should fix this, but is there anything else I should be looking at?

[Killer2600]

Yeah the battery is fine. Like most of the electrical components on the bike it's new. It was reading in the 12's but the cranking slowed after a little while and I've taken it home to charge it again.
I have a couple of different relays, one has an 87 and 87a, one being N/O and one being N/C and before the O/W wire is connected I would get battery voltage coming out, but as soon as the O/W was connected it would immediately drop to 8.
I put a new ground on the frame just ahead of where the battery box mounts under the tank. I have not yet looked at the negative battery terminal ground but I will check that.
The bike did run prior to the mod, but after the mod it only ran for about 10 seconds and ran substantially worse than it did with factory wiring before it died and I haven't been able to get it running since.
It was my understanding that not having full voltage at the coils without the relay mod was a common issue, so when I saw that I was getting 8, I assumed it was attributed to the age and possible condition of the wires and loss due to the numerous connections, plugs, and other wiring components.
The coils are grounded via the two mounting bolts that go through the frame?
Does the issue I'm having with the spark not being consistent on only one of the new coils sound like it's strictly a voltage issue? I know I should fix this, but is there anything else I should be looking at?

Should recheck how you wired the relay in, you shouldn't be getting 8V at the coil if the relay mod is working and the battery is at 12V.

Depends on the coils, if you have the coils that have two spark plug wires coming from each coil then they are grounded through the spark plugs and not to the frame. If it's just the one plug wire per coil then they use a frame ground.

[pdqford]

I checked the voltage going into the relay and it will pull battery voltage through until I connect the O/W wire. Once that's connected (while key is on and killswitch set to run) the voltage immediately drops to 8v. Something obviously isn't quite right. Any ideas?

FWIMBW, my idea is that with the O/W wire disconnected you are reading open circuit voltage (which doesn't mean anything except the circuit is not under load, and will therefore show battery voltage. When you connect the O/W wire the circuit becomes loaded (i.e, circuit is flowing current). That is when the circuit drops voltage through the load of the coil/s and circuit connections. With the circuit loaded, use your DMM and look for voltage being dropped accross the kill switch, the ignition switch, any connections in between, and between the coil/s and ground.