A little electrical story/help please

[Bobmiddle]

Ther is a little bet of a story behind it I hope some one can help.

It all started with a squeeling noise coming from what I thought was a belt or idler pulley. Took her ( 03 MM a?b? built 05/03) in to the L/M dealer that I had been going to since I bought it. Thought it would be an ez fix. The service writer called me back and said it was the alternator making the noise and to replace it and the belt it would be $700:eek:. I asked what the price of the alternator was he said $420. I grew up around cars so I asked all the right ?s is that new or rebuilt or do you have a auto electrical shop that you use to rebuild. He said that is the cost for a rebuilt one. I than made a call to a local ford dealer for a price quote on the alternator $220:confused:. I called the L/M dealer and said don't touch it I'll pick it up. When I picked it up there was no more squeeling for about 2 days. Meanwhile I was doing research on up grading to a 200amp alternator. If I have to get a new one might as well upgrade. I found a Co. (Lincoln Auto Electric) on line that sells 200amp 12v unit for the MM. I talked to the guys there to make sure it was a direct fit. He said all I needed to do was fab up a secondary led wire to the battery. So I told him to send it out and got the wire and a new belt (gatorback) to do the swap out my self. (F@#$ the L/M Dealer). The next weekend I had the alternator in my hands to do the swap. Took the old one out and set it side to side with the new one to make sure it would fit. Holes and bracket were all in the same place looked good except it was 1in. deeper......... did not fit. I found this out after having to take out the fan housing and cooling system tubes ( I dont know exact name) It hit the front of the intake manafold. It was about 1in off and I had to work in the AM so I put it all back together with the new belt. I put the new belt on because if the dealer was going to screw me it might not even be the alternator. I have not heard a peep since. But today a hot day in Las Vegas about 110 I was sitting at a stop light with the a/c blasting I look down and my volt meter is at 11v? And now that is my question WTF? I did a little problem solving if I turned the a/c off it shot up to 13v and if RPMs were at or over 1000 volt meter read 13v with or w/o a/c. I am thinking it is the alternator going out like the dealer said. From what I have read on this sight you guys know your stuff. What should I do?

[Drewstang]

11V is okay with a load on the engine like A/C. The fact that it shot up to 13V at 1k suggests to me the alt is not bad. You would need to load test the charging system to be sure. Auto Zone used to do this for free.

[Smokie]

My opinion is indeed you have a bad alternator, an alternators output is not always all or zero, I suspect you have one diode that is bad or it's breaking down under load.

If you have reason to distrust the reading on your gauge get a volt meter and read directly from the battery, with every OEM accessory on, your voltage should not drop below 12 volts in idle (during testing, I don't mean let it idle for an hour) in Drive.

If it drops to 11 vdc you either have a bad alternator or battery.

[larryo340]

^^^^^^+1
You should test the voltage at the battery terminals with a multi-meter, at idle it should not drop below 12V with all on as Smokie said. If you give it a little throttle it should be in the high 13V or even 14V. If not it will drain the battery slowly.

[MM_BKK]

Sounds like from your original squealing problem was you had a bad belt. The dealer wanted to charge you $700 to change it and as a bonus they'll throw in the alternator. WOW! What a deal! Good thing you didn't take them up on that offer. You shouldn't have anymore squealing from the Gatorback belt that you put on.
As for 11V reading on the factory Autometer gauge, don't trust that gauge. The gauge is strictly for show, especially the oil pressure gauge. On my car, sometimes it would show 10V and if I tap it, then it would jump to 13V. Get a Scangauge II, it's much more accurate.
If your Battery light did not light up, your voltage is ok. The Battery light will light up when your system voltage drops below 12V.
The factory tune has the idle set low (about 550 rpm). When you're idling in gear with lights on, AC max, your voltage is going to be lower than 13V naturally. When your rpm is at 1000 and your voltage went back to 13V is perfectly normal.
Your original alternator is probably ok. If you have doubts, take it to somewhere to have it checked. Most parts store have a bench testing set up that can test your alt in a few minutes.
I would say if you're reading at least 13.5V at the battery with a digital voltmeter with the engine idling and all acc. off, your alt. is ok.

[magindat]

True, stock gauge is BS. Either replace it with autometer lite or an Aeroforce scangauge.

Many have complained (and I do, too) of low volt at idle. I turned up my idle in drive to 900 and it helps.

[Bobmiddle]

Thanks guys that will help