Replaced Alternator / Volts still to Low......

[Manewaymja2]

Hi there

With the original Alternator on my 87 Mustang the car use to show that it charged right about where it should of been untill i changed the Pullies to underdrive and then the V meter on my dash started to show like 10 - 11 and would drop lower when running lights etc. even when i put the power windows down. If i accelerate the gauge would show like 13V or more but on stoping in trafic (coming to Idle point) the gauge would drop once again.

I changed the Alternator to a sigle wire alternator (wired up right) and the problem presist. I even went as far as to change the Serpt Belt thinking it could of been sliping. The problem is still there. When i tested the Batery with the Multi Meter the car was at idle 700 / 750 RPMS and the meter read 11.9 / 12.0 V. I also put the + lead on the one wire lead on the Alternator and the - to a body ground and came up with the same results (11.9 / 12V).

Whats left to do? its driving me crazy. I also run a 6AL MSD and dont want to run to low on Volts with that.
Help me Please??????????????

 

[jrichker]

Do not depend on the dash voltmeter for voltage information while troubleshooting problems. Use a quality DVM to get reliable results.

Single wire alternators a a poor choice for something that needs good power at idle. Most of them don't start putting out good until you get up past 1500 RPM. That's why I would only recommend a common 3G for an alternator upgrade.

If you do not get an improvement to 13.8 - 14.2 volts at 1500 RPM, start looking at the ground and power feed wire.

Be sure to use a 4 gauge power feed wire with a 125 amp fuse connected to the starter solenoid as shown in the diagram.

Starter solenoid wiring 92-93 Model cars and earlier models with high torque mini starter.

The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges.

Any car that has a 3G or high output current alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects. The 3G has a 130 amp capacity, so you wire the power side with 4 gauge wire. It stands to reason that the ground side handles just a much current, so it needs to be 4 gauge too.

The picture shows the common ground point for the battery & extra 3G
alternator ground wire as described above in paragraph 2. A screwdriver
points to the bolt that is the common ground point.
The battery common ground is a 10 gauge pigtail with the computer ground
attached to it.

Picture courtesy timewarped1972

Correct negative battery ground cable.

 

[Manewaymja2]

Do you think i can just have my original Alternator Bumped up to more amps and put that back in ? Also i put the single Wire Alternator in by just cuting the Two big Wires (they come to one on the Conector / Mechanic told me this / Black strip Red) on one of the wire harness from the original hook up and tied on terminal of Alternator. Is that ok or is could that be a problem as well?

 

[jrichker]

If you have an alternator that puts out more amps, you need bigger wiring to carry the amps.

The only exception to this is if you have really good insurance and want to see what an electrical fire looks like...

Check the power and ground wires and fix them if they are not the right size or don't have good connections.

Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 65 amps. That is a total of 190 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.

See the Stangnet 3G install sticky 3G Alternator Install: A How To - Mustang Forums at StangNet for more help on the wiring.

 

[Mike85000]

Something to think about is that even if you upgrade the alternator, it will still have a RPM threshold at which they cannot produce sufficient charging voltage. Even though you have a higher output alternator, it's threshold RPM is probably similar to the stock one. Lose the Underdrive pullies and I bet your problems disappear.