Modded Mustang Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
114 Posts
Discussion Starter #1
The new battery I put in 2 days ago was just the tip of the problem. The battery light came on and a "Check charging system" display came on the instrument panel.
I don't have equipment or knowledge to do this so took it to a trusted repair shop.
The alternator was putting out zero current. New alternator also putting out zero current but on the bench-check, it put out correct voltage. That leaves the PCM (computer) as the culprit. It's going to cost $1200 for a re-man computer.
Has anyone had this issue ? Any comments ?
 

·
Noob
Joined
·
828 Posts
Current is amps not voltage. Thats why when you test it shows voltage. I'd say to check all the wires going to the alternator.
 

·
Registered
Joined
·
227 Posts
Doubt it is the computer. Could have bad alternator (even new one), bad cables, a blown mega-fuse (I don't know if our stang's have these), corrosion, pcm relay and/or other fuses.

Did you get any codes or funny stuff popping up leading to the dead alternator. Things like abs light, airbag light..

In any case if the car runs on a charged up battery even with the alternator unplugged your computer is fine.
 

·
Registered
Joined
·
13,628 Posts
I'm a little confused. You bench tested it and got 13-14 volts right? But when it's in the car you get nothing at the battery, correct? That means it's either your alternator cable or you ECM is telling the alternator the battery is full. There has to be a sensor or whatever that let's your computer know that the battery is full, or thinks it's full. That would be where I would start. I don't think that the actual computer is bad unless the voltage sensing is in the actual computer.
 

·
Registered
Joined
·
140 Posts
i think you should get a second opinion. new parts aren't always good parts. thats a fact. maybe your alternator passes a bench test but can't handle the real world "load" similar to a bad battery. shows proper voltage with a generic voltmeter but still cant handle the electrical load of starting. is your car exhibiting symptoms of actually having a bad alternator or low battery like slow cranking, erratic gauge operation, dead battery? or is it just notifying you but everything functions properly so far? my alternator went out recently and i didn't get a "check charging system" warning. it would barely crank after a nights rest, or 8 hrs of work. the gauges would be slow to react after initial startup. if you are getting the warning but everything checks out, maybe the ecm is going haywire, but if you are experiencing actual problems, then i would double check that alternator and battery/alternator connections. sorry about the novel, i'm a yapper
 

·
Registered
Joined
·
13,628 Posts
i think you should get a second opinion. new parts aren't always good parts. thats a fact. maybe your alternator passes a bench test but can't handle the real world "load" similar to a bad battery. shows proper voltage with a generic voltmeter but still cant handle the electrical load of starting. is your car exhibiting symptoms of actually having a bad alternator or low battery like slow cranking, erratic gauge operation, dead battery? or is it just notifying you but everything functions properly so far? my alternator went out recently and i didn't get a "check charging system" warning. it would barely crank after a nights rest, or 8 hrs of work. the gauges would be slow to react after initial startup. if you are getting the warning but everything checks out, maybe the ecm is going haywire, but if you are experiencing actual problems, then i would double check that alternator and battery/alternator connections. sorry about the novel, i'm a yapper
Your alternator doesn't have to handle any electrical load while starting your car. Who told you that?

I was assuming that if it was bench tested at a shop and they said it was Ok that boy the voltage and amperage was good. They are supposed to test for both. A bad diode can cause sporadic performance. It can look perfect one time and then crap out the next time and then be good again.
 

·
Registered
Joined
·
2,043 Posts
^ Oh Yeah!^ Diodes can test good and fail under load or after heated up. I test a lot of diodes and rectifiers and sometimes have a bad part that consistently checks good, but is bad. On certain systems when this happens I will sometimes just replace the rectifier or diode that I ''think'' is the culprit with great success. This, after using test equipment that supposedly puts the component under a load during testing.

I repair electric vehicles, forklift trucks, and their chargers for a living...some propane and diesel too. I put up with this bullshit all the time. New, defective parts are quite common these days with everything being outsourced to 3rd world **** holes to be built. We have some parts that we just will not buy anymore because of constant defects. We end up getting OEM items in this case it's so bad.

Also, you don't want to install a new alternator and just drive off with a weak or even partially discharged battery. This can strain a diode and cause it to fail. Not always, but it happens.
 

·
Premium Member
Joined
·
22,435 Posts
Also, you don't want to install a new alternator and just drive off with a weak or even partially discharged battery. This can strain a diode and cause it to fail. Not always, but it happens.
Very good advice right here guys. Listen to this man! You want to put a trickle charger on your battery. If you're charger has a digital readout than it'll be really easy to know when you're good to go.
 

·
Registered
Joined
·
114 Posts
Discussion Starter #10
Thanks for all of the advice guys.
The car is still at the repair shop. They are not open on weekends so the earliest that I will know anything else is tomorrow.
 

·
Registered
Joined
·
114 Posts
Discussion Starter #11
On the mechanic's forum the repair shop used, reported computer problems after installing after-market alternators. Since they had just installed an after-market alternator, they didn't take the chance of frying the new computer and ordered an alternator from Ford. Ford sent one wrong one and then another wrong one. Today the correct one is expected !
We'll see what happens.
 

·
Registered
Joined
·
114 Posts
Discussion Starter #12
The problem is resolved.
The after-market alternator installed by the repair shop fried the new computer. They replaced the alternator with a Ford unit and put in and flashed another computer. This time everything worked properly.
The lesson learned is that after-market alternators should not be installed in these cars
 

·
Registered
Joined
·
13,628 Posts
What brand alternator did you install? Plenty of guys are running the PA 130 amp units on their cars without any issues.
 
1 - 15 of 15 Posts
Top