Electrical Issue - Overvoltage at WOT

[Raptor_]

2005 EB with the 4.6L V8

History- June or July of last year I had been having problems with the alternator not charging. Battery and alt were replaced, was fine for a couple days, then problem returned. A couple more alternators and another battery (under warranty) and the problem seemed to keep popping up within a week or so - mostly not charging, once it was producing overvotage. Finally got the mechanic to replace the tensioner pulley and belt, and everything has been fine since... until yesterday.

While accelerating to merge into traffic, all the alarms started going off and everything on the dashboard reset (instrument panel, radio, HVAC, etc.). Driving along the street, everything seemed okay, then a couple minutes later when goosing the throttle to make a gap for a left turn I got the same effect again.

This morning, I took a look under the hood. Top of the battery looked damp, and there was a lot of green, powdery corrosion under the boot around the positive terminal, and some whitish around the negative.
I put a meter on the truck (via the factory 12V accessory outlet in the console), and engine off I was about 12V. Started up and at idle I was at (I think) 14.6V. Quick blip of the throttle, and the meter shot up over 18V (may have been higher, my digital meter has a bit of a delay), the alarms went off and the electrics reset. Dropped right back to the normal range when I let off the throttle. Rolled the throttle up gradually as high as 3k RPM, and everything stayed rock steady. Tried a quick blip again, and it shot up over 16V and again all the alarms and everything.

I went over to talk to my mechanic about it (right next door, so it's faster to walk over), and she said she'd have to take a look at it, but didn't have time to do so today. She's not sure if it's the PCM, some other wiring issue, or the alternator itself, though she's hesitant to look at that since it went through so many a year ago.

Any ideas?

 

[Rick]

I would start by cleaning the battery and corroded battery terminals and replace the cables if needed. You really can't diagnose charging issues until you have a good clean connection to the battery.

 

[imp]

@Raptor_ The likely explanation, and @Rick is right on, is that corrosion around battery terminals has more electrical resistance than normal, which causes a small "voltage-drop" across the cable terminal and the battery post. The voltage regulator interprets that as a very "low" battery, since it's "looking" directly between the two cables, jacks up the output of the alternator, that sudden jolt of current through those wet resistances suddenly breaks them down, and the output climbs way too high: PCM don't like that, calls out the riot squad.

Clean up those connections shiny-bright, coat them with vaseline or grease, and tighten them well. See what happens. imp

 

[Raptor_]

So you think the corrosion on the terminals is causing the PCM to read the voltage slower? Everything is normal unless there's a rapid change in RPMs. I was thinking the corrosion and wetness on top of the battery was a symptom (due to overcharging and boiling of the electrolyte) rather than a cause.

 

[shucker1]

So you think the corrosion on the terminals is causing the PCM to read the voltage slower? Everything is normal unless there's a rapid change in RPMs. I was thinking the corrosion and wetness on top of the battery was a symptom (due to overcharging and boiling of the electrolyte) rather than a cause.

Green stuff on positive post is actually Copper Sulfate. Negative is Sulfation.

Yes you are correct from boiling electrolyte. Thus, turn if you have a crappy connection what will happen?

Alternator \ PCM will misinterpret readings and drive the voltage higher and the process will compound itself.

 

[imp]

Green stuff on positive post is actually Copper Sulfate. Negative is Sulfation.

Yes you are correct from boiling electrolyte. Thus, turn if you have a crappy connection what will happen?

Alternator \ PCM will misinterpret readings and drive the voltage higher and the process will compound itself.

@shucker1

I tried to say that...... imp

 

[Raptor_]

Well, cleaning the terminals is certainly an easy enough thing to try, but over the course of this year there have been three different batteries in the truck, and this is the first time I've seen any corrosion at the terminals, so this certainly wasn't something playing a factor until recently.

 

[TechGuru]

What make/model alternator are you using?

I'd get a BOSCH AL7541X

 

[Raptor_]

They've all been remanufactured alternators from a local shop my mechanic has always used. Didn't have time to take care of it myself when the first failure occurred, so now I've got one under warranty from them.

 

[TechGuru]

They've all been remanufactured alternators from a local shop my mechanic has always used. Didn't have time to take care of it myself when the first failure occurred, so now I've got one under warranty from them.

Honestly would not surprise me if that is your problem... I've had many problems on other vehicles with re-manufactured alternators.

Bosch does not make a new one for the 4.6L V8 but REMY does.

 

[Raptor_]

UPDATE - So... my mechanic's spent a day looking at it, and a few days chatting with their colleagues trying to find a solution. Ultimately, we couldn't find anything external to the alternator, except a suspicion it may be related to the PCM. I bought what was claimed on the phone to be a "new" alternator from an area Ford dealership, but when I arrived at the parts desk, the clerk said they only have remanufactured alts for my model, though at least it comes with a 2-year, Ford-backed warranty. After installing the "new" alternator, I took an 500 mile drive, and everything seems to be just fine.

Here's the bit that's got me wondering though...
When looking at the service manual, there was a passage that stated that, "The generator output current is determined by the voltage of the A circuit 35. The A circuit 35 voltage is compared to a set voltage internal to the regulator. The regulator controls the generator field current to maintain the correct generator output."
It also said, "The set voltage varies with the temperature and is typically higher in cold temperatures and lower in warm temperatures. This allows for better recharging in the winter and reduces the possibility of overcharging in the summer."
All of the failures I had were in late June/early July, both last year and this, when the weather first starts getting hot. Any thoughts if this might be part of it?

One of the mechanics at my shop thinks it might just be related to all the driving I do, and that I just put a lot more demand on those inexpensive remanufactured parts than their typical clientele who mostly just do short commutes around town, whereas I fairly regularly bounce around within a six-state area.

 

[Raptor_]

For the sake of reference, in the last six weeks I've put on about 2,200 recorded miles, plus little around-town driving.