02 Ford F-150 4.6 5-speed FX4

I have searched the internet and have found several different causes for a Parasitic drain but nothing that has pin pointed mine? I am looking to the experts to help. About a Month ago driving down the road my odometer reading looked dim and than the battery light came on. I got home and grabbed the volt meter and with the truck running was at 11.6V across the battery. Classic bad alternator was the first thing that came to mind so I purchased a new one from Oreilly auto parts and put it on. Cranked the truck, 14.3v were good to go. Next morning got up to go to work and the truck was dead? Jumped it off, drove to work (25 miles) so it charged well. Came out from wok and it started no problem. A couple days go by no problems then it was dead again (cold night). Battery is a year old and I actually swapped the battery out of my Mach 1 and it killed it too? (trouble shooting along the way) I put a volt meter between the positive post and cable and seen a 3-4 amp draw. Pulled fuses and figured out #11 under the hood (Alternator field) dropped it 200ma then to 30ma after 30 min or so (goes to sleep). This doesn't happen all the time though and it seems to be the voltage regulator, I can unplug it directly from the alternator and stop the draw. I took that alternator back and exchanged it but I am getting the same results? Sometimes it does it but not always? I guess my question is, does the PCM control the voltage regulator in any way? Another note, my ABS light comes on "sometimes", I just replaced both front bearing hubs with new ABS sensors. The light stayed on all the time before that and now just sometimes. Not sure if that has anything to do with it but it's the only other thing that's weird. The truck runs great with no other drive-ability problems so I have no other clues? My first thought is to take the alternator back off, get a refund and try a different store? These are new, not refurbished. I have read about the GEM module and thought it could be that, and I also replaced the battery saver relay when I first started the trouble shooting. Any ideas would be greatly appreciated, these types of problems are very aggravating. Thanks

 

With no ideas on the long post I posted here is a short question? Is there any way that the PCM is making the alternator draw current from the battery after the truck is shut off? I know it controls most functions on the alternator but is something in between them after the key is out of the ignition?

 

I don't know exactly how it does it, but the truck has a "sleep mode" that after some time ( 1o- 15 minutes) the PCM shuts down all amp usage to a very low level.. not just the alternator, everything... So it appears your "timer" does not always work.. How that occurs, I don't know.

 

The PCM has...NO.. control over the charging system.
The GEM does timing after shutdown for some functions.
If you remove the connector off the Alternator and drain drops to the normal level, you still have a faulty regulator, Alternator, bent pins at the connector..
The only "power" in play after the ignition switch is off is the link between the alternator and the battery.
The alternator has a diode bank and field windings that are a connection to ground for the drain.
When the motor is shut off and alternator in not turning, these are supposed to go open.
If that does not happen, you get a drain condition.
An alternator that charges is not necessarily fault free and must be checked for drain.
Good luck.

 

Thanks for the reply. Like I said in the first post I replaced the Alternator 2 times already but after doing some testing yesterday everything comes back to the regulator like you said. The other factor was there was never a problem until the original alternator went bad (probably the regulator). I should have just replaced that instead of the whole alternator. It's been hair pulling but I have learned some things along the way for sure. I am out of town till Friday but I will post my results after I change the regulator out. Thanks again

 

Just a thought here, but are you sure they gave you a different alternator? When you exchange that one make certain they give you a different one.
The Orillys auto parts around here are usually staffed by 19 year old gear heads that don't know a nut from a bolt. They know how to install cold air intakes and fart can mufflers, but don't know anything else.
I learned a lot in the last few months chasing a battery drain on my wifes expedition. I have a long post on here about it. I learned that I had been doing the draw test wrong. I also learned that my meter was bad. Just for thought here is the procedure I ended up using. Disconnect a battery cable. Put a jumper wire between the post and the cable. Connect the meter between the battery post and the cable, then go have a cup of coffee or three. Come back 45 minutes later and pull the jumper wire. Before you leave it for the 45 minutes click the door latch in the door to closed, this will shut off the dome lights. I learned it takes over a half hour for the timer to shut everything off. I was doing my test after 15 minutes of waiting and getting all kinds of strange readings.
Also, check the fuse block under the hood, make sure there is no corrosion behind the fuse block that could be causing a short.
The alternator should not drain, so it sounds pretty certain the diodes in the alternator are bad. The diodes are a sort of one way bridge that allows current to flow from alternator to battery but won't allow current to flow the other way.

 

I learned a looong time ago to always have them test alternators and starters in the store before I take the part home.

The last alternator I replaced, on my 2000 Conturd, failed the in-store test at my local Oreillys. Straight off the shelf, still sealed from their rebuilder.... If I'd have had to replace that thing a second time (it's a huge PITA due to its location up against the firewall), I'd probably have just blown the car up. The local store found another store nearby with the alternator in stock, had them test it and, when it passed, I drove over to the next city and picked it up. It worked in the car.

Point is, test the part before leaving the store to prevent further problems.

 

Thanks again for the replies. I got back in town and removed the alternator and took it back to Oreilly's and got a refund (no questions asked). Remember, that was the 2nd new, not refurbished one from Oreilly's so I thought I would try Autozone. Bought a new Duralast Gold and the problem still exist so it's somewhere in the wiring I guess? I put the new one on, drove for 20-30 min came home and checked the battery voltage 12.68, and then went to cut the grass. 2 hours later I was at 11.98 (battery is about shot now) and the Alternator was very warm (much warmer then other engine parts by far) and magnetic on the pulley. Any other testing procedures are welcomed while I go do some wire testing and checking connections everywhere. TIA

 

Well after digging more I can only come to the conclusion that all 3 alternators that I have put on the truck charge fine but the regulators are bad? I can pull the #11 fuse that is hot all the time cause it's supposed to be and the drain goes away. The regulator is supposed to close the circuit off when the the pulley stops turning but it's not. Please let me know if my thinking is wrong? I am going to order a Motorcraft voltage regulator and if that doesn't fix it I will roll into the river! If it does (and I think it will) fix it, I will be completely reeducated on the charging system and cheap auto part stores alternators! The diagram I made notes on is for a 99 but the alternator wires are the same (I think). The 99 had an inline fusible link where 02 has another junction box under the hood.

 

Did you or did you not have the most recent alternator tested before you took it home? Did you have O'Reillys test the one you returned?

As I told you, I'd learned that the HARD way a long time ago, you'd do best to take advantage of that experience so you don't have to continue learning things the hard way on your own.

You're doing a lot of guessing but not doing simple things that will corroborate your hunches.

 

They did not test any of the alternators but I also don't think the tester will/can catch the voltage regulator problem? All 3 alternators charge just fine, all had 14.xV + output. This problem takes hours to happen and the people working at these places barley know how to hook it up to the tester. The first one I took back to Oreilly's was tested before they gave me a new one and it tested fine to them. I had them run it 5 times and it did the same thing 5 times. It spins the alternator up and checks output. My thoughts in the voltage regulator test are it only checks to see if the output voltage is within a tolerance?

 

project SHO89 ........... im wondering if someone has ever thought of adding a diode to the wire so the alternator can push out, but not let current run backward to ground when off ... This would be an AFTERMARKET diode.......... I guess that's basically what the regulator is suppose to be doing.

 

I guess I still don't understand the PCM function 100%.. If it takes 30 minutes for the system to go into shutdown mode, then its NOT just the alternator stop turning that shuts off the feedback. It seems it would be possible for SOMETHING inside the PCM to also have a problem ?

 

That's what I thought too (a possible PCM problem)? Bluegrass posted this "The PCM has...NO.. control over the charging system". He went on to explain that it has no control after the ignition is off and that makes sense. I pulled the #11 fuse yesterday and the battery is stable this morning. In the diagram that circuit keeps the alternator hot all the time (by design) but it should not do anything until the pulley turns and excites the other circuit back to the regulator then the system works together? Just my thoughts? I will replace the regulator with a Motoecraft and if that doesn't fix it a new PCM will be installed.

 

Refer back to your schematic.
Where you marked 'back to PCM I guess' is not correct and is just a guess.
There is no connection to the PCM in the dash or elsewhere for any type control during these year trucks up to about 2008 or 09.
The GEM I mentioned takes power direct from the battery and has nothing to do with the charge circuit.
If you change PCM it will be costly for no gain.
Back to the box again.
In the small box you see the transistor emitter is grounded.
When this transistor is biased on, that ground make the dash lamp turn on.
As soon as the alternator output come up, that transistor is biased off putting the dash lamp out.
.
The actual regulator function is even a separate function within the regulator.
Within the big box you see 8 diodes and a capacitor to ground.
The diodes are reversed biased in the circuit configuration that makes them normally non conductive. Of course the capacitor does not conduct DC either.
If any of these element begin to conduct from a breakdown fault, they provide a drain path from battery to ground.
The regulator can also separately go into a fault condition and cause a path to ground.
You can begin to see that even if the alternator turns at engine speed it can still develop an output with faults in either of these two circuits.
A catastrophic short to ground is provided for by the fuses so the truck does not burn up, in that case. But some times it does happen if insulation burns before the lead opens and starts a fire..
.
One way to test the diode performance is to look at the battery voltage when the motor is running, with a voltmeter set to AC. If the diodes are faulty, a significant AC voltage will be detected by the meter. You can even look at the voltage with an Oscilloscope and see the AC and amplitude developed.
The AC that rides on the DC should only be a few to about 10 milli volts depending on the health of the Alternator diodes and battery.
I can tell you from experience that this can be seen as I have done it a few times looking for noise on my Amateur radio installation to see if a custom built filter is doing the job of filtering out the noise on the battery supply to the radio.
To repeat, a charge system can still charge but still have one of these faults mentioned above.
If the dash lamp goes out, you can assume the alternator is outputting and the regulator is detecting it and putting the dash lamp out.
Otherwise there can still be an issue in either device.

Be happy at this point your not having an issue with a 2010 and later truck where the PCM does control the charge system, provides codes, then what would you do?
I just feel something is being missed. The clue most valuable is how fast the drain occurs. If the diodes are leaky or the field winding is still connected after shutdown, the drain will be high for short time drain of the battery.
Otherwise drain much lower such as a interior lamp would take much longer to run the battery down.
I would still use the series Lamp test to detect a drain after the GEM has gone into sleep mode in about 45 min or longer just to be sure and remove the under hood lamp from the socket..
If the low wattage lamp lights from the drain, disconnect the heavy lead at the alternator.
If lamp goes out or dim, there is the fault in the charge circuit.
If no, the drain is somewhere else.

Good luck.