F355 Newest Alternator situation! - Ideas?

A "dead" connection for your sensing wire is what is killing your voltage regulator...no voltage there causes your alternator to spike to max output, frying the v-reg.

What Wolftalk and others were saying on one of your earlier threads was to connect that sensing wire to the battery output wire (you've always got voltage there) to see if that would bypass your problem.

 

Wow, this thread has gone on a long time! As I can recall, you've replaced the large cable to the starter and added several grounds and jumped the battery disconnect switch. By connecting the sense wire to various points and running the wire back into the passenger compartment, you've been able to bypass the rest of the harness. Is that correct? Have you measured directly off the alternator? Does the battery light on the instrument cluster provide a bootstrap current for charging? You would check that by reading the alternator output voltage after disconnecting the small gauge wire that connects to the battery warning light. I ran across something today on a Mercedes list:

"One problem in putting a warning light here in the circuit is that an automotive alternator, unlike the old DC generators, uses steel in the field pole pieces (the rotor on an alternator) that don't hold residual magnetism, so a "tickler" current is needed to start the generating process when starting the car. Also, if the field circuit opens up, output drops to zero. The GM circuit uses a fairly large shunt resistor across the warning light bulb to assure tickler current if the bulb fails."

So what would happen if the wire to the instrument cluster (battery light) were to short to ground or short to full battery voltage. It might explain the very bright indication and abunch of other stuff lighting . Would the output from the alternator stop, ie drop from 14 to 12.4? Incidently, sometimes the alternator does output 16 volts to charge the battery. So what I would try is checking alt output voltage without the without the battery warning light. Let us know what happens next.

And you've also replaced the battery in case there is an intermittant open. If all else fails, you could bypass the harness and run a positive cable from the alt all the way to the battery and then use it to verify the ground connection to the battery.

I spent a day and a half tracing a problem in a fuel injection system on a 911 and it turned out that the volt meter had too low of input impedance and it was affecting the oxygen sensor output voltage. After getting a 10 megaohm dvm, everything was fine. That which doesn't kill us makes us stronger. Good luck!

Jeff Pintler
89 348(major almost done), 86 TR (won 1st in a car show today)

 

What was the results of your voltage tests while running the car with the fault present?

 

Dumb idea, but I'm famous for them:

Could it be 8 miles, or could it be X minutes ?
(however many minutes it takes you to go 'about' 8 miles)

 

The fault may be a the alt/reg, a battery going open circuit, or more likely a wiring connector issue/hi resistance problem somewere...

The process to fault find your problem in a methodical manner has already been posted. I apologize if what I wrote hasn't been understood.

With it being a continuous fault it is defintly traceable, given a bit of work and some patience.

Good luck.

 

one question, is the RPM gauge connected to the alternator like on classic range rovers? if so, once i had a friend with frecuent alternator problems and after checking EVERYTHING it turn out to be a problem with the dash itself
not likely and a long shot BUT you never know, good luck

 

Just a suggestion but, have you tried bypassing the starter? I don't know if it has anything to do with your alternator, but maybe something to do with the connection there. There reason I'm TOTALLY GUESSING this is because on the early 348s there is a bullet style connector running from the battery to the starter. If the connector somehow were to get loose, or come undone, the car would run on the battery, and not the alternator, until the battery went dead. Ask me how I know. So maybe the path from your alternator to your battery follows the same path as on my 348, Alternator -> starter-> battery? To me it is a dumb way to route power to the battery. Maybe, just maybe it has something to do with the soleniod in the starter that is giving you all the grief, or something having to do with the path the power is following, rather than the alternator itself? It could be back feeding the power or something? Again, totally guessing here?

 

Remember that the cig lighter is probably connected to the fuse panel which connects to the battery through a large gauge wire directly through a fuse. The reason I was suggesting running a fused line directly to the alternator terminal is so you will bypass all of the cabling that ties back to the battery and you could find out exactly what the alt is doing. If you can, you should get a wiring schematic for your car to better troubleshoot where the problem might be. At the risk of being too direct, the alternator does NOT feed the cig lighter socket! You could have a bad fuse panel or bad fuse or bad cable from the battery to the fuse panel. You could also have three problems and they mask the solution to the problem. Also remember that if the alternator sees an open load (or no load as in open wire) it will toast itself. One fun experiment might be to connect an extra load like a fog light to the alt output terminal and aim it so you could see it in the rear view mirror after you verify what the alt is at the terminal. That way if the connection all the way back to the battery had an open in it the alt would still see a load and the alt would output 14 volts (p=ie so i=p/e=55w/13v= 4.5amps). You are fighting a difficult problem. That which doesn't kill us makes us stronger. Good luck.

Jeff Pintler

 

AAAAAAAHHH! Don't give up. You're gonna to have to go through the entire wiring and find where the problem is. Having the dealer do that is gonna cost you some retarded money, and they may not even find anything. If you really are at your wits end, then go get your car and take it to a good auto electric shop and have them trace the problem.

 

Sorry we couldn't help you resolve this. My big splurge was a two post lift and it makes things alot more fun. The delco unit on the TR has one small wire for warning lamp and a large terminal for output (regulation is internal). The nippondenso (sp) unit on the 348 has one large wire to the starter, one small wire(1.5mm) to the bat warning lamp, one small wire to ignition switch (guessing run position) and one small wire all the way back to the battery (connector 85 on the schematic). Boy, I'd sure be tempted to make a small jumper for the "s" terminal (R color code) and connect it directly to the battery. AFTER CONNECTING A FUSED SMALL WIRE TO THE LARGE CABLE BETWEEN THE ALT AND THE STARTER to monitor the output voltage. Looks like there is also a five pin connector (called engine devices connector #115) that the S terminal cable passes through that could be corroded (the wires to the Battery warning lamp and to the ignition switch also pass through the same connector). Alot of times a connector with a poor connection will carry current for a short time, overheat and then loose connection. That is why I'm suggesting jumping the S terminal since the Bat warning lamp works. The "IG" terminal wire goes all the ignition switch (15b) and may have power when the key is in the run position. I would hate to think the previous alternators couldn't be tested properly because of two small wires that need power to charge the battery! Anyway, sorry we couldn't solve this one.
Good Luck!

Jeff Pintler
Darn it!