Help with fluctuating voltage

[subysti]

I have a 96 5.7 mercrusier with a 2bbl carb. This year after its winter storage the voltage is fluctuating. At idle with nothing else on its fine at around 13.5 volts. I turn on the nav lights and it drops to 12.5, add the blower and radio and its below 12 volts. If I have nothing on but run the engine up to 1500 rpms it again drops to about 12 volts. I've already replace the alternator. I did notice that the wire for the electric choke was not connected to the alternator so I connected it accordingly but that just made things worse. According to the shop manual the choke should have the pur/yel wire and a ground attached. there is no place to attach the ground though. anyone have any ideas? I did all the testing according to the shop manual on the 1st alternator and the voltage regulator should it needed replacing, it was putting out 15.5volts. The new one seems fine though. Is something else fried? Help Help.

 

[Don S]

Re: Help with fluctuating voltage

Have your batteries load tested. Did you ever check the water level in them? At 15.5 for any period of time, you will boil the water out of the batteries, without water, we call them junk.

 

[bruceb58]

Re: Help with fluctuating voltage

Are you measuring these voltages right at the battery?

 

[subysti]

Re: Help with fluctuating voltage

When I was testing the alternator I was getting the voltages off the alternator itself. The rest of the time I reading the dash gauge.

 

[JustJason]

Re: Help with fluctuating voltage

SubySti..... what are you using for a meter?

BruceB58... haven't seen ya post in a bit. Good to see you after our little disagreement.

Subysti..... First thing to check is obviously all your conections are clean and tight. you need to make sure they are by using your meter to perform a voltage drop test. You should perform it on all of your charging and starting system circuits (loops)... or wires... depending on your definition. Google "voltage drop test" to learn about it. Ya should also do an AC ripple check just to make sure. Just because you put a new alternater in doesn't mean its any good.

SubySti.... what one you got? I got a 98 GC8 body style. Custom motor, 05 RS bottom end, 00 legacy heads, custom grind cams done by COBB... It's natrually asperated but pushin 220psi compression. Sounds like a desiel on cold mornings and is a real torque monster for its size. its also got full STI V6 suspension, a whiteline adjustable rear bar. F&R strut towers braces. List goes one...

But back to topic... what meter are you using?

 

[subysti]

Re: Help with fluctuating voltage

Meter is a Fluke 87 III. I'm an electrical engineer for I have all the tools except a good high amp meter. My meters only handle 20 amps.

As for the car I had an 04 Sti, wrb/gold rims but it really wasn't anygood for towing. Had all factory options, fog lights, gauge pack, armrest, etc etc.. Really no mods excepts for the K&N CAI and kenwood stereo system.
So now I have a VW touareg V10 twin turbo diesel. Gets great mileage for such a big heavy truck but at $5.00 a gal its killing me.

SubySti..... what are you using for a meter?

BruceB58... haven't seen ya post in a bit. Good to see you after our little disagreement.

Subysti..... First thing to check is obviously all your conections are clean and tight. you need to make sure they are by using your meter to perform a voltage drop test. You should perform it on all of your charging and starting system circuits (loops)... or wires... depending on your definition. Google "voltage drop test" to learn about it. Ya should also do an AC ripple check just to make sure. Just because you put a new alternater in doesn't mean its any good.

SubySti.... what one you got? I got a 98 GC8 body style. Custom motor, 05 RS bottom end, 00 legacy heads, custom grind cams done by COBB... It's natrually asperated but pushin 220psi compression. Sounds like a desiel on cold mornings and is a real torque monster for its size. its also got full STI V6 suspension, a whiteline adjustable rear bar. F&R strut towers braces. List goes one...

But back to topic... what meter are you using?

 

[subysti]

Re: Help with fluctuating voltage

Could it be a problem with the starter? I've heard of them having dead shorts in them even thought they still work. I notice that the output lead from the alternator goes directly to the starter then branches off to the breaker and the battery.

 

[buggiedad_67]

Re: Help with fluctuating voltage

have your batterys tested and while you are at it check your belt a loose belt will show up the same way, as you put more load on it the belts slips more then a drop in volts.

 

[Coors]

Re: Help with fluctuating voltage

I have a 96 5.7 mercrusier with a 2bbl carb. This year after its winter storage the voltage is fluctuating. At idle with nothing else on its fine at around 13.5 volts. I turn on the nav lights and it drops to 12.5, add the blower and radio and its below 12 volts. If I have nothing on but run the engine up to 1500 rpms it again drops to about 12 volts. I've already replace the alternator. I did notice that the wire for the electric choke was not connected to the alternator so I connected it accordingly but that just made things worse. According to the shop manual the choke should have the pur/yel wire and a ground attached. there is no place to attach the ground though. anyone have any ideas? I did all the testing according to the shop manual on the 1st alternator and the voltage regulator should it needed replacing, it was putting out 15.5volts. The new one seems fine though. Is something else fried? Help Help.

Is this a used Boat? Wired wrong?

 

[Coors]

Re: Help with fluctuating voltage

I can't seem to copy just a part, to quote.
you hooked the choke up and it got worse, sounds like somebody before you re-wired, the not correct way.

 

[bruceb58]

Re: Help with fluctuating voltage

Could it be a problem with the starter? I've heard of them having dead shorts in them even thought they still work. I notice that the output lead from the alternator goes directly to the starter then branches off to the breaker and the battery.

If it was a dead short you would have a LOT of current flowing. That is not your problem obviously.

The reason that the alternator lead goes to the starter is becasue that is where the heavy lead that goes to the battery is connected. The alternator output could just as easily go directly to the battery and operate the same.

Have you looked at the schematic in your manual to see if everything is hooked up?

 

[subysti]

Re: Help with fluctuating voltage

Thanks for all the info. Here is more from my end. Yes it is a used boat but this is our 2nd year with it and it was fine last year. Here is what I did tonight. Loosened and re-tightened all the wire connections and the drive belt for the alternator. checked all the wires and found 3 ground wires not connected to anything, I'm assuming they were this way last year as I cannot even find a place where they way have been connected. Here's the results. With engine running I get ~13.8 volts on the dash gauge and 14.48 volts with my meter connected to the battery. I turn on the running lights and the dash gauge drops to ~13 volts but the battery is at 14.43 volts. I then turn on the blower and the dash goes to ~12 volts but the battery goes to 14.38. So it seems the wiring to the gauges may be at fault because all the gauges jump a little when I turn something else on. It does make me worry that maybe the temp or oil pressure may not be accurate. Here's the real odd part. In looking at the wiring I did find a purple/yellow wire that was not connected to the alternator and it connected to the electric choke. When I connect it to the alternator the voltage at the battery drops to 12.45 volts. The schematic shows 2 wires going to the electric choke but there is only one connection on it for the purple/yellow wire. Does anyone have any pictures to maybe show where there are supposed to be 2 wires? How about why its killing the voltage? I'm thinking the previous owner had it disconnected for just this reason.

 

[bruceb58]

Re: Help with fluctuating voltage

All the things you are turning on are being powered from the fuse panel loacted near your helm as is the voltage guage at the helm. You are basically noticing the voltage drop between the battery and the fuse panel at the helm. There is a connector at the engine that has many connections including the wire that feeds this panel. This and a few other spots are places you need to check for your voltage drop. Since you are a EE, you should have no problem isolating the drop. Check your ground return as well.

 

[subysti]

Re: Help with fluctuating voltage

thanks for the help Bruce. Unfortunatly there doesn't seem to be a fuse panel anywhere on the boat. There is a big round multi-pin plug on the engine and then all those wires run to the guages up front with inline fuses. Any ideas on the electric choke problem? BTW the boat is a 1996 Larson Lxi 190.

 

[Don S]

Re: Help with fluctuating voltage

Have your batteries load tested. Did you ever check the water level in them? At 15.5 for any period of time, you will boil the water out of the batteries, without water, we call them junk.

Did you have the batteries load tested?