| Author | Message | ||
     Todd Phenneger (Toddp) Member Username: Toddp Post Number: 184 Registered: 10-2002 |
Heya guys, I have a really wierd Alternator Problem. First a quick history of the problem. Vehicle is US Market 1994' Discovery V8. 80k miles, New Magneti Marelli Alt from Dealer before I purchased car. 125,000 miles. - Last Tuesday Christmas Eve the 24th. Alternator Dies. Tach was jumping around all day then went totally bad. I had battery checked, battery is 2-yr old Intersate and is fine. Sourced a rebuilt Beck/Arnley unit from NAPA for $300 and put it on. Great, Alt works so I head 300 miles accross the mountains. 2 days later the alt dies again, slowly, takes about 1 day to fully die. Oddly enough both times the Alt died the Charge light never came on. Wierd. Well, Spokane Napa has one alternator available so I have it shipped to me and swap it in. Now tis faililng as well. Syptoms, WHEN the alt works I get 13.8 - 13.9 Volts output. When its NOT working I get nothing. Just battery voltage whatever that happens to be. I can see when it dies by watching the tach signal as when the Alt is not charging the tach reads 0. I have checked groudns, and voltage drop accross the ground and power wires. I get about 50-70mv on the ground and about 250 - 300mv on the power wire depending on load. 300mv with stereo on, lights on, fan on high, defroster on, aux lights on etc. That seems withing spec, I have not had an opportunity to check voltage drop while the Alt is NOT working however. Does anyone have any ideas. WHats going on? ANY Ideas are welcome. Thanks Todd Phenneger (stranded accross the mountains) | ||
| Chad Meyer (Ccdm3) Member Username: Ccdm3 Post Number: 187 Registered: 07-2002 |
I used a rebuilt alternator before and had the same problem. I now have a new genuine one with no problems. FWIW | ||
| Todd Phenneger (Toddp) Member Username: Toddp Post Number: 185 Registered: 10-2002 |
I had some more time to probe around with the DMM both with the Alt working and not working. What I have found is that all grounds, and power wires appear to be good. However, the brown wire that goes to the center terminal on the alternator changes. This is above the output for the tach but below the primary +wire that goes to the battery. When the Alt is working it gets +12v. When its not working it sees about 0.6v The values are with the ignition in ON position. Doesnt matter if car is actually runnign or not, I get the same readings. I can only assume that this wires is a keyed signal wire that tells the alt to turn on. However, in my Crappy Haynes Manual that I have with me the wiring diagram differs from what I show. It doesn't even show this wire or the Tach wire on the wiring diagram. Wierd. So, where does wire feed from, what fuse is it on and is there an underdash connector anyone knows of where I can test as well? Thanks a bunch for any help Todd (still stranded in spokane, with 10" fresh snow and no rover to play in it with) I did get SOME playtime though after buying a battery charger adn charging for a few hours outside the Hotel. :-) | ||
| Chris Browne (Chris_browne) Senior Member Username: Chris_browne Post Number: 515 Registered: 02-2003 |
Todd: I've not yet had to change out the alternator but from reading this list for a few years, seems that the rebuilds out there aren't worth the money...so get a brand new one from the dealership | ||
| Dave Thomas (Dthomas) New Member Username: Dthomas Post Number: 23 Registered: 11-2003 |
The BOSH rebuilt Marelli is about the only 'reman' that I would go with. Its first rate. | ||
| Todd Phenneger (Toddp) Member Username: Toddp Post Number: 186 Registered: 10-2002 |
UPDATE! I'm on third alternator. But this time right after replacement we checked the entire charging system. (much easier inside a shop when its not 0-degrees "f" outside. :-) Seems there was about an 800mv Voltage drop accross the wire from the Alternator to the Battery. Fuse was fine but somewhere after the fuse there was a lot of resistance causing the alternators to heat of massively and frying them. So, after adding a 4-ga power wire from battery to Alternator, the 3rd unit seems to be working fine now, is not overheating, and I'm getting better voltage at the battery. Moral, when you change out your failed Alt make sure to check the voltage drop across your power and ground wires. Supposedly about 100mv on the ground and 300mv on the power wire is the upper limits. That is with alternator on and fully loaded. IE...lights on, stereo, rear defroster, heater fan, etc all on high. I was showing about 50mv on the ground side (fine) and about 250mv on the power unloaded but obout 700mv when then alternator was working hard. Thanks Todd |
