Voltage drop recently

[larryb]

My car used to run about 14, or a little more voltage. Now seems to hover under 14, any real concern???? I did add a electric fuel pressure gauge would that do it??? any concerns running under 14???

[trichardson]

A fuel pressure gauge shouldn't have any affect your overall voltage as they draw very little current. Is the voltage that you're talking about the voltage that you see on the dash voltage gauge or are you reading it with a handheld voltmeter?

It's supposed to run about 13.5 at idle and up to the mid to low 14s above idle. If the battery is staying above 12.5 when the car is turned off your probably alright for time being though if you aren't seeing 14s when the car is cruising you may have a regulator going out.

[larryb]

dash voltage gauge, used to always run higher when driving now doesn't get to 14, should I check voltage elsewhere, i do have a meter (i think I know how to use it )

[trichardson]

Try checking the voltage at the battery with the engine off and with the engine running to confirm what the dash gage has been telling you. If the readings are the same the regulator in your alternator might be on the way out. If the readings are different but the difference between the off voltage and running voltage is the same you may have loosened a connection to the gauge when you installed the fuel pressure gauge (or something like that - hopefully someone more knowledgable will chime in).

[BigLeo69]

sometimes the 1 wire alternator will surge the voltage

[larryb]

Yes have one wire alternator , what does surge the voltage mean, would that make my voltage decrease??? Is a regulator replaceable or will I need to replace alternator??? should I just watch voltage before getting out the wallet??

[STROKER ACE]

Check every hex nut on the charging system and every ground on the engine block , good luck

[steve_mk4]

X2 on what trichardson said.

If the voltages are the same with the engine off and running, your alternator or regulator are bad. Most modern alternators have the regulator built in and you just replace the entire unit.
You should have around 12.5 volts with the engine off and somewhere around 13.5 to 14 volts with the engine running. I would expect to see about 1.5 to 2 volts higher with the engine running.

[Bill Hughes]

Its supposed to do that...temperature coefficient, and the outside temperature is going up.

It will go back up when the weather cools down.

[mike covey]

I had an alternator (O'reilly) fail over almost a year. The voltage just got lower & lower. Finally had starting problems etc.

[larryb]

OK will ck

[tirod]

One wire alternators don't charge until you get them up to speed, usually over 1,700 rpm. So, you might be seeing a difference between it coasting along and actually working.

Normally, the alternator "S" wire is connected to the main load point to signal the regulator. A one wire doesn't do that, it never knows. It just turns off and on as it revs up - which is why it's a tractor alternator, not suitable for car use.

A volt meter reading low? Just the tip of the iceberg that will slowly freeze up the operation of most of the electrical system. Bonneville racers found out that typical wiring will corrode so badly by the third year of exposure that it has to be completely replaced. That's only a 30 day window each year, not that many actual runs. It only takes a few hours parked in flood water to total a car. It's even illegal to sell them because they keep getting worse.

All that really happened was to accelerate the corrosion process we somehow accept as normal, when it's really planned obsolescence. Just say no to primary wire and donor harnesses.

[larryb]

Ok??? Well i cked voltage at battery 12.5 with engine off and 14.1 with engine on at the same time meter reads about 13.9, I did splice my fuel press gauge into the power suppling other gauges could that have changes the voltage reading at gauge. I'm not too worried now that battery reads fine, just know volt meter is a little low???

[trichardson]

Read the voltage at the splice with your handheld meter and compare that to what your dash meter is reading. If they are the same then your have a voltage drop in the wire feeding the dash gauge and other instruments. It could be that you damaged the wire when you spliced it or the splice is no good and is resisting the voltage down. It could also be that the fuel pressure gauge is drawing more current than it should pulling the voltage down though that's the least likely problem I'd think. If the readings are different then your gauge dash volt meter is reading a little low.

[tirod]

12VDC wiring is highly sensitive to wire size, condition, and connection. First - it's only 12 volts. That's about 10% of the electrical pressure of household current. It is literally lame - commercial trucks run 24VDC - but it won't kill you messing with the battery cables.

It's traditional, and it works, but there's not much leeway. A ten foot length of wire can easily develop enough resistance to eat one volt. The connection alone can, and the circuit also has to be well grounded. That is a connection, too, back to negative. You can easily lose 2-3 volts in a long run to a turn signal.

New car owners who trade in less than ten years never see it as a problem, those of us who drive collectible cars (sometimes before the public views them as such) live with it daily. The standard wire system in cars is the minimum acceptable method of getting it done - factories aren't going to drop one more dime on it than necessary. The specialty builders are starting to change, BMW has a fiber optic connected mulitplex system in it's high end cars. Things are changing because of the demands of computers and costs coming down. But in large part, what was installed in a '62 Chevy is the same as a '74 Pinto is the same as the donor harness from a '94 Mustang.

Corroding junk.

[larryb]

So with time U may get a slow voltage drop???? corrosion etc???

[Bill Hughes]

As I mentioned before...WAIT TILL WINTER...IT WILL GO BACK UP! The regulator tracks the ambient termerature and adjusts appropriately, as it should.

[AustinSnake]

12.5V off and 14.1V running sounds about right...and trichardson has it, the 0.2V difference at the gauge is likely due to voltage drop in the wire supplying the gauge w.r.t. where you measured under the hood.

Could also be inaccuracy in the gauge itself, but unlikely. Measure the voltage at the gauge with the same meter. If the 0.2V delta is also observed by the meter, you have voltage drop in the wire supplying the gauge. If not, the gauge and the meter disagree on the voltage...and one is wrong :-)

Brian