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84 SN2001 Voltage Drop

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maxibarker View Drop Down
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    Posted: September-24-2017 at 3:21pm
Shouldn't my electrical system be able to overcome the load of a small Rule bilge pump, and the OEM blower? I have great hole shot with these loads off, and stumbling, and stammering when I stab it with these loads on. Nominal voltage is 12v, but when loads are on it drops to 10.5. Shouldn't the available voltage regulate to maintain nominal 12v? My solution is obvious, loads off generally. But seems to me that when this boat was new I didn't have to do this. Thoughts?
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Gary S View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 3:39pm
Thoughts? do a search,common problem with all makes. You need new feeds to the dash,much like people needing a heart bypass
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 4:09pm
Sounds to me like a nominal voltage of 12 is low and maybe your alternator/voltage regulator have issues.

You should have 13 to 14 or so at the battery itself (measured with a multimeter)
with the engine running and a little less at the dash.

If that 12 is on your dash meter, it's too low

What do you have for an ignition system? points or electronic. What brand if it's electronic?

If it's electronic, depending on the brand, they can be finicky and do things like you describe if supply voltage is too low.

It could be wiring related like Gary said or the alternator/regulator or a combination of both.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 5:27pm
* Failing alternator?
* Ground or power cable corrosion and/ or short?
* Voltage regulator?

Regardless, I would verify the exact running voltage with loads off to eliminate the possibility of a failing battery and that the alternator is supplying the correct voltage while running. It's a good starting point anyway.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maxibarker Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 6:12pm
Thanks all. I did search the forum first but didn't come up with anything relevant. It's a new alternator with an integrated regulator as my "mechanic" suggested but no help. Also at his suggestion we changed out the loom resistor with a ballast resistor no help. And while we were at it we replaced the coil. Same result. It has points by the way, not EI. Will get the meter and check these suggestions and the battery is probably about 7 years old so will do a load test.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gt40KS Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 6:45pm
Battery is not to be ruled out, you're correct - stranger things have happened. As with the alternator ... brand new out of the box has been known to be faulty. I'd still check it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 7:08pm
I'm kinda wondering what you have for an engine, since you mention having a loom resistor originally and I haven't seen any mention of the brand, like PCM Ford, Mercruiser Chevy for example.

The PCM Fords didn't have a resistor in the wire loom

You could also check the big connector plug at the back of the engine, unplug it, clean the connectors and plug it back together.

Power has to get thru that plug to get to the dash and back thru the plug to get back to the ignition system and corroded connectors can impact your voltage and current carrying capability.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maxibarker Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 7:15pm
It's a Ford 351 Commander and it did have a loom resistance wire. I will clean all connectors while I try to find the problem. Thanks.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 7:44pm
I guess I won't put up Tim's PCM wiring diagram then, it may confuse things
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 8:38pm
Originally posted by maxibarker maxibarker wrote:

Shouldn't my electrical system be able to overcome the load of a small Rule bilge pump, and the OEM blower? I have great hole shot with these loads off, and stumbling, and stammering when I stab it with these loads on. Nominal voltage is 12v, but when loads are on it drops to 10.5. Shouldn't the available voltage regulate to maintain nominal 12v? My solution is obvious, loads off generally. But seems to me that when this boat was new I didn't have to do this. Thoughts?

Confirming what has already been said, clean all your connections check voltage at the alternator and then at the dash with a VOM. Up sizing both the - and + wire up to the dash is common. Also add up your amp draw and run it through one of the on line calculators like this one. When sizing wire, take a look at the chart:





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Keep it original, Pete
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maxibarker Quote  Post ReplyReply Direct Link To This Post Posted: September-24-2017 at 8:56pm
Will do. Thanks all!
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