Alternator/Battery Help?

Question

I have a problem with my car. New battery and new alternator just 3 months ago. When I am driving the battery light comes on when I have my foot on the gas and go above a certain rpm, goes back off at idle. Had bat and alt check and both are fine. New alt belt. Monro tested and reved engine, alternator ok at idle but drops like 4 volts with load. Any suggestions since the battery and alternator both new have less than 1000 miles on them. Monro suggested I might want to see an electrician because he thinks voltage is being dropped somewhere. Can someone help me? My car is a 1999 Mercury Cougar.

Answer 1

loose belt is the most common thing here
i test the whole system together test voltage at the alternator and at the battery check amps output at idle and at 2000 rpm also check amps under a load i use a 100 amp battery load tester to do this test the volt drop under load doesnt concern me as youre looking for how many amps it will put out if the volts are high at the alternator and lower at the battery concider running an aditinal 10 gauge wire from the alt to the battery or finding the weak spot in the old wire if you run a new wire make sure to fuse it with a fuse link

Answer 2

Just because a part is new, doesn't mean its not defective. I work in a garage, and I get defective parts all the time. What you are describing is sounding like the alternator, even though it is new. I would look into returning this alternator for warranty (if applicable) and installing a new one. I've seen this quite often when doing AVR tests, the alternator charges at idol, but wont do anything at higher revs. Its an internal problem in the electrical.

Answer 3

Sparky is right. Alternator is what supplies the power to your system thus it is the most important. The big 3 upgrades the current capacity of important wires which improves the amount of power your car has available. A deep cycle battery will be able to discharge fully and still be good unlike a regular battery which will be damaged greatly if you do this. Good Luck!!!

Answer 4

I would suggest that you take a look at your spark plug wires. Look for a white ash spot where the wire is near something metal. I suspect the something electrial is grounding out somewhere in the engine of your car. Spark plug wires fit the description of what you are suggesting, though you might notice a preformance change if the plug wire was grounding out. More current runs through the wires as the RPM increases because it has to generate more spark to brun the fuel, hence the High RPM issue.

Good luck!

Answer 5

The only thing that comes to mind is a loose/dirty drive belt.

Durring lower engine speeds the alternator is easier to turn, but when you raise the engine speed the belt MAY be slipping, and when it starts to slip, it slips a lot and discontinues turning the alternator.

Someone else suggested the voltage regulator.
I'm not much of a Ford man, but that makes sense too.

Answer 6

there was a service bulliten on that car and the problem is in the connector to the alternator. take your car to a electrical specialist and tell them your prob. the connector and maybe a rerouting of the harness will be the cure. I've had to do about 5 of these things and it's not an easy job.

Answer 7

As above, check the regulator. Also check all grounds on the main electrical system. It could be you have a bum alternator, especially if it's a "rebuilt" if nothing else pans out.

Answer 8

On a Mercury, check your voltage regulator, or connections at the regulator.

Answer 9

Try another alternator and check the grounds.

Answer 10

try looking at the voltage regulator