computer ground

i had a bad ground off the ecu and off the main harness. my car ran like crap. Somedays it would run ok others it wont even wanna go. The car would buck all the time and lose power etc... so look over your grounds and see whats going on. Heres a link for a complete new harness though "i'm buying one myself soon" i have some jacked up wiring under my hood, to many owners not knowing what they are doing yah know.


http://www.fordracingparts.com/parts/part_details.asp?PartKeyField=23

The ecu wire he's refering to is the the top of the engine bay harness. It's almost between the 'salt and pepper' shakers. Should be a red wire. If it's not on the block/firewall, hook it up, I put mine to the same ground on the head that the engine grounds to the firewall at.

Grounds are important to any electrical system, and especially to computers.

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.

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. It is in the fuel injector wiring harness and comes out under the throttle body. It gets connected to a manifold or head bolt.

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