F355 New Alternator Problem Now! Any Suggestions?

Ok, for those of you that have followed my alternator problems.........I removed the "new" factory fresh Nippon Denso alternator from the car, the one that would work fine (start the car....voltage would be in low 14's, then after a couple of miles of driving......voltage would settle in at 13.5, then after about 10 miles of freeway driving, the voltage would drop (over about 10 to 15 seconds) to 12 and the battery (alternator) light would come on dimly........then, a few miles later, everything would start working again, and the voltage would come back up to 13.5 and the light would go off. Then, this same scenario would happen again......over and over, with no rhyme or reason why.

Well, since then, I have replaced the 4 gauge positive cable from the alternator to the junction block in the right side of the engine compartment. I also replaced the positive starter cable to the same junction block (didn't have to do this, but it was right there and easy to do). Also cleaned and tightened all ground cables, battery cable connections (new MT 34R Interstate battery). Also, installed a rebuilt (new voltage regulator) alternator that I had rebuilt by a recommended auto electric guy that an independent Ferrari mechanic told me about.

Okay, after all this, I was curious to see what would happen. Started the car...voltage now reads about 14.4.....good........drove a couple of miles.....voltage now settling in at 13.5 or so..........good......get on freeway.....voltage still at 13.5.......good.......drive for a few miles.....voltage still on 13.5..........good.........drive a few more miles......voltage starts creeping UP.......to 14......to 14.5.......battery light now starts to flicker brightly........15.0...........15.5..............16.0 volts!.........holy Sh___! I pull off the freeway before my battery explodes!..........Voltage starts to go back down as I slow down and come to a stop and the traffic light. Voltage now back to 13.5 and battery light is off. Start driving home...........voltage stays at 13.5.........good.........drive for another 5 miles or so........voltage still at 13.5........drive another couple of miles..........voltage starts creeping up again (I am only doing about 45 MPH at this point) ...........14.....14.5........battery light starts flickering brightly..........15.0.........I slow down and pull into a residential area.......voltage comes back down to 13.5 and stays there as I go home at about 40 MPH.

What could be the problem??? It seems like something "heats up" or gets "triggered" by driving about 7 miles or so and gets the alternator to go overboard (VR not regulating the voltage). Then, after slowing down, the voltage goes down and all seems okay for another 7 miles or so.

Any ideas? I'm stumped. I called the auto electric guy and told him the above scenario. He is kind of stumped. He thinks that the sensing wire could have a problem.

Any suggestions?

 

Should I run a thick 4-guage battery type cable from the negative post on the battery to the case of the alternator? I suppose I could rout one under the fibleglass panels under the car. Why would everything work fine for 7 or so miles, and then go wierd on me?...............and then...........after slowing down, go back to normal again? Would a ground come and go like that? Also, I though about checking the battery with a hydrometer to see if a cell is bad. It IS a new battery, so I doubt that I have a bad cell.........but even if I did, would a bad battery cell make the alternator act like this........when it works and then not?

 

The A/C and all other accessories were off when I did this last drive. The left cooling fan does come on and go off (as usual), but when it did, the voltage on the system did not vary. When the cooling fan came on, the voltage stayed the same as it was, and when the cooling fan went off, the voltage stayed the same as it was.

I did not notice any "heat shield" above the alternator when I replaced it.
I suppose I could fabricate one. What material can I use?

Does anyone have a photo or schematic of this heat shield around the alternator?

 

That schematic is not of my '95 F355, and that component doesn't look like my alternator.....it looks too long. Is that schematic of a 348? I do not have that "adjustable" slotted bracket for tensioning the belt.......I have an adjustment bolt on a tensioning pulley.

 

Yeah, that does look like an A/C compressor. What can I use for a heat shield? .040 or .063 aluminum maybe? Also, would not having a heat shield cause this "7-mile" then "all hell breaks loose" thing I'm experiencing? I guess after driving 7 miles, the heat gets to the "breaking point"? :-(

TBA, what do you think about the direct ground cable idea that No Doubt has? Also, what do you guys think about checking for a bad battery cell?

How do I check the amperage while I'm driving the car? How do I check it when I'm not driving the car? Since this problem is "intermittant", won't a test of anything show up "good"?

 

I can't see the heat shield in your schematic (the one you fixed). Am I blind?

 

I see the ground strap....which I have on my car. I will do the "direct to the battery negative post" thing that you suggest. I will also fabricate a heat shield of some sort. (I don't see it on your schematic, by the way). Is the heat shield an original Ferrari part, a later "fix it" Ferrari part, or do people fabricate their own?

I will also check the ECU behind the passenger seat that TBAKowsky suggested. Anything else that could cause this "intermittant" problem?

 

Yes, it is a four-wire alternator: B+ (4-guage battery cable), then a 3-wire
plug. I assume IG (Ignition) , S (Sensing) , and L (battery light).

Would splicing in the S wire to the B+ wire "fry" the S wire?
How do I tell which of the three smaller wires is the S wire?