I noticed that the charging system voltage on the 2000 crownvic had been a little low recently. I found that the voltage measured directly between the alternator output post and the alternator case seemed good which indicated that the alternator itself was working properly.

But the voltage at the battery was too low. and i was getting a 1.5 volt drop if i connected one lead of a voltmeter to the alternator case and the other to the negative battery terminal while the electrical system was under high load.

Knowing that the alternator acquires it's ground path through the lower mounting ears and that rust doesn't conduct electricity very good, i pulled the alternator off the engine to inspect the mounting surfaces for possible sources of excess resistance.



a closeup of the road salt crust and rust scale that had formed





the mounting ears on the back of the alternator are rather corroded too



i rotated the alternator mounting bolts in the engine block mounting holes numerous times to mechanically break away the corrosion on the bolts. and then pulled them out completly so i had better access to clean up the rust on the engine block.





then cleaned up the back of the alternator with a wire brush



and cleaned up the engine block itself with a wire brush

before





after




removing the corrosion in between the alternator and the engine block lowered the voltage drop from 1.5Volts down to 0.7Volts. this resulted in significantly improved battery recharge characteristics.

there have been scattered reports of people on this message board getting several "bad" alternators in a row from the auto parts store. if you've got corrosion like pictured above, you can install all the alternators you want and still not have the charging system work properly.

eventually, you might get one of the new alternators to charge. each time you turn the mounting bolts, you mechanically break a little corrosion away from the mounting bolts that provide a ground path. and each time you slide the alternator ears onto the engine block, you mechnically break away a little rust from the engine block too. after changing out the alternator several times, you might have accidentally removed enough corrosion to make stuff work again. however, it is much quicker and much less frustrating to attack the corrosion directly in the first place.

the alternator in the pre-2003 cars can compensate for a voltage drop across the positive output wire feed. you will loose some charging capacity due to the excess resistance, but charging system voltage will stay reasonable.

however, the alternator cannot compensate excess resistance in the ground path of the alternator. all the measurements that the voltage regulator makes are against the grounded alternator case. if there is a big voltage drop in between the alternator case and the negative battery terminal, the alternator voltage regulator knows nothing about this issue which could let the battery voltage drop significantly below where it should be.

Very good job there. Maybe use some dielectric grease to keep the rust from forming again?

I wonder if extra ground wire mounted to alternator case and one of the engine grounds would help with your remaining 0.7V drop?

it helped with mine i ran an extra 4 ga wire from alt case to battery neg


i will be upgrading to 0 ga next year with a few other things


nice work on the grounds 2v but what about putting grease there like 1 man army said?

^^ x2 I have a wire connecting from the alt > right head > Batt

i made big progress getting the charging system voltage closer to where it should be.

but the 00' crownvic still has excess resistance somewhere between the negative terminal of the battery and the grounded alternator case. i'm getting voltage drop readings of 0.7V on the negative side of the alternator return path when i load up the electrical system and let the car idle. my 1998 crownvic only has a 0.3V voltage drop across the ground side of the circuit when the electrical system is really loaded up.

at some point, i'll probe around a little more with a voltmeter to pinpoint where the problem is coming from. i'm suspecting the culprit is something with the battery cable harness or the big ring terminal that attaches to one of the transmission bellhousing studs.

installing an extra ground cable to the alternator could help too. this 2000 crownvic still has it's original all-plastic intake manifold from late 1999 installed. so no grounding action goes on through the intake manifold like you'll find on cars with an updated intake with the metal coolant crossover.

The word "dielectric" means "insulating", so you shouldn't use it on ANY electrical connection. The correct grease is ELECTRICAL grease.

Better to run it straight to the battery (-) terminal. But there's a risk... If anything ever happens to the main ground cable, all the current will flow thru the aux, which might overload it & set it on fire. So use a big one - close to the size of the stock ground cable.

This is the same reason you don't want the coolant crossover to act as a ground. It'll electrolyze the coolant, causing corrosion in the cooling system, as described in the TSB in this caption:

Nice job on the mounting.

One further thought (maybe you've already done it) is to clean the threading on both the bolts and the block really good, as well as the front face of the mounting ears and the bottom of the boltheads. Lots of available electrical contact to be made there... And it could be argued that that is where most of the grounding occurs.

Just out of curiosity.
Since the Alt acquires it's ground path through the lower mounting ears, what would happen say if you replaced the engine at some point but painted the block as oposed to just throwing a bare metal block and components in a car as the factorys do now?.
Would the Alt be able to get a decent ground through the paint or would you hae to grind it off at that section to obtain a good ground.
If I ever have to replace a motor, I'd paint everything 1st is why I'm asking....

You would want to grind off the paint for a good connection.

Paint is a VERY good insulator.

Most paints are insulators. However paints from this source are conductive. Just don't howl about prices since I know they are not cheap.

http://www.2spi.com/catalog/spec_prep/cond_paints.php

Stalag

Instantly went from 12.4V at idle to 13.8 & climbing! Do you think ANYONE has that kind of paint on his alternator or block? And if he does, do you think he'll be reading this thread?