Voltage Jumping Around - Signals Blinking Slow

ImportSlayer347 said:

I'm thinking bad ground somewhere. But seeing as there are a million ground points and connections...where should I start?

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Yes, it does sound like you have a bad ground so check the connections of the ground cables coming from the engine.

Grounds
Grounds are important to any electrical system, and especially to computer controlled engines. In an automobile, the ground is the return path for power to get back to the alternator and battery.

1.) The main power ground is from engine block to battery: it is the power ground for the starter & alternator.


2.) 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 , computer, & 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.


3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to its proximity to the battery, it may become corroded by acid fumes from the battery.
In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
You'll find it up next to the starter solenoid where the wire goes into the wiring harness.


4.) All the sensors have a common separate ground. This includes the TPS, ACT, EGE, BAP, & VSS sensors.

5.) The O2 sensor heaters have their own ground (HEGO ground) coming from the computer. This is different and separate from the O2 sensor ground. It is an orange wire with a ring terminal on it. It is located in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or bolt on back of the cylinder head.

6.) The TFI module has 2 grounds: one for the foil shield around the wires and another for the module itself. The TFI module ground terminates inside the computer.

7.) The computer takes the shield ground for the TFI module and runs it from pin 20 to the chassis near the computer.

8.) The computer's main power ground (the one that comes from the battery ground wire) uses pins 40 & 60 for all the things it controls internally.


See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



Extra grounds are like the reserve parachute for a sky diver. If the main one fails, there is always your reserve.

The best plan is to have all the grounds meet at one central spot and connect together there. That eliminates any voltage drops from grounds connected at different places. A voltage drop between the computer ground and the alternator power ground will effectively reduce the voltage available to the computer by the amount of the drop.

The alternator also has an internal voltage regulator that could be going bad.
JMTC

dagenham said:

The alternator also has an internal voltage regulator that could be going bad.
JMTC

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True, a lot of the quicky parts places will test the electrical system on the spot for free. Of course it never hurts to clean the grounds as needed.

Has the alt been load tested yet?

If so, the wiring to the alt might need to be wiggle tested.

The same advice applies. Have the alt tested and make sure the power cable is not loose.

Have you done the voltage drop testing of connections and grounds as described in my first post to your problem? If there are any problems with bad connections, this will find them.

Sure sounds like your voltage regulator is going bad (internal or otherwise).

ImportSlayer347 said:

Today it started jumping up too, not just down. It hit 16.5 for a brief second then dropped.

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BlackGT89 said:

Sure sounds like your voltage regulator is going bad

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x2, and the voltage regulator is held on the back of the alternator by two small Torx bolts so it's very easy to replace.

Are the faces of the mounting ears shiny metal? If not, that could present an issue.