Alternator question

[88Stangboy]

Ive been having trouble with my car ever since i got it running again.
I havnt really had to time to go over it since i drive it mostly at night and thats when it breaks down...
But basically, the alternator isn't charging the battery, its a 3G and i put it in about 6 months ago, so could it have went bad already? The left headlight has been dim at night, the bulbs are brand new. The car runs on battery basically and im wondering if its the voltage reg. or something, its driving me crazy. It went dead three times tonight already, i've borrowed one battery to get home, the one i've always had in there is brand new also, then i had to hijack the battery out of my explorer. Im just wondering if i have a short or something that could contribute to this? Thanks

 

[HISSIN50]

You can take the alt to the parts store for repeated bench testing.

Absent that, go over the wiring. When I swap an alt, I replace the regulator plug since those wires tend to vulcanize.

Make sure your motor ground is sufficient (A tip from Jrichker is to add a 4 AWG power ground).

Good luck.

 

[88Stangboy]

Welp, i just went out and poked around under the hood right quick, cause i really need to drive the car in the morning. So, i figured out that a ground wire had snapped on the left front headlight and it wasn't grounded. I temporarily grounded it and the headlight came right back on. As for the atl. not charging i looked and the adjustment had slipped on it as to where the belt was slipping on the pully. So problem solved.

Thanks Hissin50 for replying though. I was goign to dread having to pull the alt. just to have it tested. As of today im broke...a bad alt. was going to be bad news.

 

[88Stangboy]

One more question though....
If my engine ground isn't sufficiantly grounded, can it possibly cause a mis-fire?

 

[HISSIN50]

I think I hit your other thread with some info from Jrichker on the grounds. I feel that depending upon where a missing ground is, it definately could cause an issue of sorts. More likely to cause a misfirish kind of problem is that a ground is insufficient. It would not be high on my list of things (FWIW, the injectors get key-on 12 volts, and the computer controls the ground pulse to each one to fire them). That might clear up some of your concern.

But adding an extra motor ground is always a good idea. The factory grounds are barely adequate new, let alone after some years. I just added a 4 AWG to the 94, which had a decent ground (intended for a 3G) to start with. It helped.

I am glad you got the headlight and alt squared away. Do you run a set up with V-belts? Otherwise I dont recall any adjustment with the stock alternator bracket/bosses, nor with the serpentine belt (the latter is self tensioning).

If you have a conventional set-up (serp belt), it takes about 5-10 mins to remove the alt - future FYI.

Good luck with the miss.

 

[JimBowy]

Here's my suggestion, although this diagram is for a battery relocation, the basic grounding locations are shown....

 

[88Stangboy]

Yep, V belt.

Thanks for that wiring diagram. I upgraded to a 3G and i never upgraded the engine ground, it has stock grounding, etc. That may be where most of my problems are steming from. Im definatly not an expert on electrical, but im trying my best to learn. Thanks for all your help, its really helping me alot.

 

[dec322]

I'm searching the threads right now trying to learn and solve some problems.

Has anyone heard of grounding the battery to the "computer"? I just bought a 1988 mustang today and the guy has a ground wire (looks about 4 gauge) running to the computer. Does this sound right?

I'm having an issue with the voltage of the car dropping at idle thus causing the rpms to rise in order to keep the car from stalling. The guy just replaced the battery yesterday but I think he may have misdiagnosed (<--spell check?!) the problem. I'm thinking alt. won't know till I test it.

 

[jrichker]

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 alternator, 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 cylinder about 2 1/2" long by 1" diameter with a black/lt green 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

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