one'mo'gain....chassis grounds, engine grounds, battery grounds

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 A/C compressor clutch and other electrical accessories such as the gauges. Any car that has a 3G alternator needs a 4 gauge ground wire running from the block to the chassis ground where the battery pigtail ground connects.

3.) The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. . It is a black cylindrical quick disconnect with a 6" or so pigtail from the battery negative post.

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

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.

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

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://www.fluke.com/application_notes/automotive/circuit.asp?AGID=1&SID=103#volt for help troubleshooting voltage drops across grounds

Jrichker-
Where do you put the ground for the 3G? Is that the one at the back of the block to the firewall? I never up graded that one...only the alt to starter sol when I did my 3G upgrade...maybe that been my problem with low voltage with the fan and lights on...sorry of topic...

mustangsquared said:

Jrichker-
Where do you put the ground for the 3G? Is that the one at the back of the block to the firewall? I never up graded that one...only the alt to starter sol when I did my 3G upgrade...maybe that been my problem with low voltage with the fan and lights on...sorry of topic...

Click to expand...

The extra 3G ground goes from the engine block to the chassis ground point near the battery. You'll find several grounds from the battery tied to one bolt or screw. That's the place to connect the extra ground to the chassis. The engine block end location isn't so important. I would use the block batttery ground or the A/C compressor mount as a ground point.