Hey guys. I have an alternator problem that no one around here can figure out, so I'm throwing it out to you guys. Please bear with me, it's kind of a long story. Over the past couple of weeks, my alternator gauge has been slowly moving into the red (on the low side), until it finally went down too far to ignore. Took the alternator off, took to Advance Auto to have it checked. It was bad. Ordered a rebuilt one (that's about the only kind you can find now) off of ebay. It came yesterday, I put it on....and same problem. So today I went and bought a rebuilt one locally, from Advance. Put it on.....same freakin thing! Here's what it's doing. The volatge is fine in park, at least most of the time. But when you have a load on, like the a/c and the cooling fans, and put it in drive, the alternator doesn't put out at all, it just reads the battery voltage. So I drove the car to Advance to let them test it on the car, and altho it tested fine in park, when you put it in drive they get the same thing....no voltage being put out by the alternator, and my gauge goes down into the red. And when I got home, I tried my remote start. It would start, but the low gauge reading made it stop every time (it has to be at a normal level for it to stay running or it automatically cuts off). Anyone have any ideas at all on this? I'm really stumped!

 

Does it do the same thing in drive when the a/c and cooling fans are NOT on? I know there is a wiring harness going into the tranny on the passenger side but not sure if there is anything in the tranny that could cause such a draw of power. A motor on a fan could be going bad causing it to pull down the amps. What are the rpms of the engine doing when the guage is going into the red?

 

If you have a bad alternator, and it made the battery bad, or the battery was bad already, you would strain the new one to deal with the weakened battery, and will end up with a bad alternator again... Or it could be a bad alt. too. The former seemed to be what happened to me. Did you have your battery tested? Everyone ought to consider getting a plug-in battery charger which tells you the charge % and power level.

Also check your belt and tensioner, to ensure that's working well as they are key to the alternator working and battery charging.

 

the ignition switch may be failing. the alternator needs to have power going to the little wire that plugs into the back before it will kick in. check it to see if theres any damage to it or if its shorting to ground. may be that when its put in gear the motor pushes on it and grounds it somehow. check the wire for power when the motors running and in gear.

 

Thanks for the responses guys! The battery was tested at the same time the alt. was....battery is excellent. RPM's are normal when the volts go down. I just got up and I'm going out to work on it some more. First I'm gonna check the tensioner, I know if it's freezing up it would cause the problem. Then I'm gonna take the alternator off and take it down and have it tested to rule that out. I'll check the other suggestions as well, and I'll update later on today. Any more suggestions, please feel free to leave them. Thanks guys.

 

Ok here's an update. Alternator bench tested good, close to 15 volts. I also put a new serpentine belt on just in case the other one had stretched a bit. Here's what the car does. If the car is in park, when the cooling fans come on high speed, the gauge shows right at 13 volts. In park, the rpm's are about 750. In drive or reverse, when the fans come on high speed, the gauge drops in the red zone. In drive, the rpm's are about 650. If I hold the brake and give it gas to get the idle up to 750, gauge goes back up to 13. So the problem seems to only occur when the car is in drive and the fans come on high speed. So does this tell me that one or both of the fans are going bad and drawing too many amps, or the idle speed in drive needs to be adjusted up a bit? I assume the idle speed is computer controlled, so I'm guessing the fans?

 

unhook the wires at the fan and try it, if no change pull the fuse/relay for the fans and see if the discharge problem goes away. dont let it overheat so the fans are the only thing it discharges with? headlights, stereo, heater fans, they dont make it fail? do you have underdrive pulley's on the motor?

 

No underdrive pulleys. All stock except for an SLP fan control switch. And before anyone asks, the voltage drop occurs when the fans come on whether I turn them on manually or they come on automatically. But I can sit at idle with the headlights on, stereo and radar detector, and a/c on max with blower fan on high, and the voltage only drops when the cooling fans kick on. Assuming that it's one or both of the cooling fans, is it best to just buy the whole setup (both fans and motors in the housing that just slips in), or just try to find new motors for them?

 

i would sure consider taking the switch outa the circuit to make sure theres no short or its not wired wrong. with that kind of discharge (its sucking up the 40-70 amps the alt is putting out and draining the battery) i would suspect a short and/or stuck relay. the motors should be really hot after doin that if its the fan motor failing. if its the wires the motors would be cool to warm and the wires heated to the problem area. like i was saying if the wires are the problem i would think if you unplug the fans at the fans the problem would not go away. could be wrong though. lol. the relay may not come on without a completion of the circuit or draw of power from the motors, that i dont know. easy way would be to pull the fans, take em in to be tested. alt shop should be able to run a amp draw test on em. should be able to pick up a fan setup used or change the motor. cost probly the same sense the fan setup would be used.

 

Thanks craby. I am going to check and make sure my relays and wires are good, and try and check the things you said. But I think if it is one of the fans, I am going to buy the whole setup new. I'd hate to spend $100 on a used setup that's 10-15 years old and probably have the fans or motors go out again sooner rather then later. I see I can get the whole setup new for around $160. I'll post whatever I find as I'm working on it today.