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Impossible Voltage Drop at Coils

  • Thread starter Thread starter MisterCinders
  • Start date Start date
M

MisterCinders

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After another weird power loss, I revisited my ignition wiring and am stumped. The power loss happened the other night after 20 minutes of riding. Bike went lat (like it lost 2 cylinders) and would die with the clutch in, bump starting back up when in gear. I limped to the side of the road, and the bike would only stay running (and then pretty badly) if I kept the revs up at 4,000+. Sticking to city streets to limp home, the problem faded away after 15 minutes or so, just as I returned to the garage.

The high revs made me think the charging system might have drained the battery - yielding electrical power only when the RPMs were above 4,000 - 5,000. When I checked for a depleted battery, however, she came back with 13.5 volts. I hooked up the trickle charge anyway, and it charged for <30 minutes before beeping to signal full charge.

Lat time this happened, I had a bad coil. This time, testing the coil resistances comes back clean. No shorts, all resistances in spec. In fact, I cannot seem to recreate the power loss, that started this (but it's too cold to ride much so . . . )

Here is what I can find. A significant voltage drop between the battery and the coils.

Battery is fully charged, shows these results:

13.5 volts key off.
12.75 - 12.90 volts with ignition on
10 volts at coils

Note that 2+ volt drop is with a coil relay. Wiring the coils through the harnes gives me a slightly bigger drop (about 3-3.5 volts).

I replaced the relay, and rewired the the link between battery to relay, and relay to the coils. Even with fresh wires, soldered connections, etc. I cannot get above 10 volts at the coils.

After seeing this problem in another thread, I triple-checked that I had the pins correctly wired for the relay. They are good.

So where else could my wiring be shedding that kind of voltage?
 
Did you try battery to coils directly, with a separate piece of wire?
 
Check the voltage at the battery input terminal and the output terminal at your relay. They should be identical to battery voltage. How did you wire up the relay, specifically terminals 85, 86, 87 and 30?
 
Where are you getting the switched power source from for your relay?
 
850GT_Rider said:
Did you try battery to coils directly, with a separate piece of wire?
Click to expand...

Not yet.

koolaid_kid said:
Check the voltage at the battery input terminal and the output terminal at your relay. They should be identical to battery voltage. How did you wire up the relay, specifically terminals 85, 86, 87 and 30?
Click to expand...

I'll check that out. I wired the relay according to this diagram:

COILRELAYMOD1.jpg


I've had the relay set up for quite awhile now, and it worked great until this happened.

azr said:
Where are you getting the switched power source from for your relay?
Click to expand...

The switched power comes from the O/W wire that used to power the coils. With the relay, though, a voltage drop in the ignition switch/kill switch should not show up at the coils, should it? I thought that so long as the voltage was enough to trip the relay, the juice from battery -> relay -> coils superseded others.
 
MisterCinders said:
Battery is fully charged, shows these results:

13.5 volts key off.
12.75 - 12.90 volts with ignition on
10 volts at coils


I replaced the relay, and rewired the the link between battery to relay, and relay to the coils. Even with fresh wires, soldered connections, etc. I cannot get above 10 volts at the coils.


So where else could my wiring be shedding that kind of voltage?
Click to expand...
It would have to be because of the relays contacts, fuse contacts or under sized wiring.

MisterCinders said:
COILRELAYMOD1.jpg


I've had the relay set up for quite awhile now, and it worked great until this happened.
Click to expand...
'This happened', sounds like to me, crud stuck in the the needle valve and seat which resolved it's self.
 
MisterCinders said:
Not yet.



I'll check that out. I wired the relay according to this diagram:

The switched power comes from the O/W wire that used to power the coils. With the relay, though, a voltage drop in the ignition switch/kill switch should not show up at the coils, should it? I thought that so long as the voltage was enough to trip the relay, the juice from battery -> relay -> coils superseded others.
Click to expand...
Your diagram is a viable way to connect the relay (there are several). All the switched wire does is activate a coil, which closes a set of points. Then battery voltages go from terminal 30 to terminal 87.
Check those voltages. Check your ground while you are in there.
 
Hmm, very perplexing. I think I agree with Koolaid. Sounds like a fuel issue more than electrical. But so hard to tell with these problems. You might want to carry a spark plug wrench and a small meter with you for the next couple of months or in the spring. You can troubleshoot a lot with just those two devices like am I getting fuel to the sparkplugs? Am I getting spark? BAttery good? Do I have a short, yada yada. You know.

How bad you guys get hit this weekend? See any damage in your parts?
 
Sci85 said:
Hmm, very perplexing. I think I agree with Koolaid. Sounds like a fuel issue more than electrical. But so hard to tell with these problems. You might want to carry a spark plug wrench and a small meter with you for the next couple of months or in the spring. You can troubleshoot a lot with just those two devices like am I getting fuel to the sparkplugs? Am I getting spark? BAttery good? Do I have a short, yada yada. You know.

How bad you guys get hit this weekend? See any damage in your parts?
Click to expand...

Thanks for asking. I am in the city and have a brick home (wolf problems in the past), so we came out OK.
 
Good to hear. Nasty and weird to get that kinda weather this late in the season. With the flooding and tornadoes, you guys are taking a beating this year. Wonder if you'll have another epic snowfall like a couple years ago...
 
There was someone else here recently that had a very large voltage drop after installing a coil relay mod. Turned out he miss read the p
 
posplayr said:
There was someone else here recently that had a very large voltage drop after installing a coil relay mod. Turned out he miss read the p
Click to expand...

I saw that thread and hoped to find the same problem. Alas, my wires were connected to right pins.
 
MisterCinders said:
I saw that thread and hoped to find the same problem. Alas, my wires were connected to right pins.
Click to expand...

Not sure it is very likely you could get a 2V drop across a relay even if it is possible. With that big of a drop you should be able to measure significant resistance through the contacts. That would be about 0.5 ohms for the ignition circuit (i.e. 4 amps)

Note that 2+ volt drop is with a coil relay.
Click to expand...
 
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