signs of a failing altenator?
 

weird situation here. with all accessories off. The car idles at about 700-690 rpms and feels "lumpy" with minor pops pops.. so i was like...shit... apex seal... HOWEVER.. when the head lights are turned on the car idles smooth as a mofo with only very minor miny pops. the idle also goes up to 820 RPMS.. I then disconnected the battery when the cars running and the car runs fine.. as soon as i flip the headlights on.. Instant stall.. IS that normal? Shouldnt the altenator be able to supply the demand? IF i tap the break the car trys to stall as well.. The thing that dosent make much sense to me is why the car idles so much better with the Friken headlights on.. :/ Help.

eletrical sh!t will act bonkers with a failing alt. warnings with come on, and the car will want to stall.

Make sure you have GOOD connections on ALT. before buying a new one.

here is a hint, you can take off the alternator and take it to any Checkers or local automotive store and they should beable to have it tested for free and/or diagnosis it for free. same goes with starters.

good luck

before you do all that, just do a general check

bust out your dmm (digital multimeter) and with the car running, check your battery with the probes

should read 14 point something if its getting a good charge

thats a good start before you go nuts with ripping stuff apart and having people charge you to do the same thing

When you disconected you battery did you disconnect both terminals? If you did then thats the problem there. You should only disconnect the positive side. If you disconnect the neg. side you are taking away a major ground.

If you did disconnect correctly then yes, it should be your alternator, or as someone said you may have a bad connection to the alt.


The reason your car idles better with the headlight on is because once you turn them on you increase the load to the alt. there by increasing the rpms that your car is running at. You should have the same result by keeping your headlights off and barely pressing on the gas to increase rpms by about 100rpm.

If that doesnt work... sorry but im out of ideas.

Thanks for the help guys, I love this forums.. Replys with helpfull advice QUICK :D...

Anyway, i didnt disconnect both terminals, I only disconnected the positive side. Ill check the terminals tomorrow when i have more daylight.. i think im feeling to sick to go to work anyway ( cough cough ) :).

Anyone got any other suggestions.?

I think lots of times alternators are replaced and are not the problem. Simple test, Run the engine with everything off. Measure the voltage at the battery. It might be between 13.5 /14.5. Then turn on the loads. Measure the voltage at the battery again. It should be over 13 volts. If not the battery plays a big part in what the alternator does. If the battery is sulfated/has resistance in the core it will effect the voltage regulators signal and change output voltages as well as smoking alternators. The signal from the battery can confuse the regulator and cause the alternator to work harder than it should thus burning it up. The best test for a battery I found besides load and electronic resistance is battery capacity test. I learned this in college 25 years ago from my tune up teacher.
Connect the battery to a charger. Charge at 20 to 25 amps. Normally thats what charges use. Watch the voltage rise from 12.? and up. If after 3 minutes the voltage is above 15.5 volts, replace the battery. I also keep the charger on for a while longer maybe 30 minutes and if the voltage reaches 16.0 also replace the battery. I 20 years of tune up and electrical work to back up this testing. I use the new testers and often they don't detect faulty battery's but this one always does. A battery (12volt) has 6 cells each 2.1 volt. If one cell is bad the voltage will read 10.5 and larger capacity battery's will still start a fuel injected car at this low voltage because they have so much amperage as back up. A correctly charged battery will read 12.6 or a bit higher. Sorry for going on but this is really important stuff.
The FD also has a electrical load sensing module and should compensate for these loads and if it is a skew the idle speed wont be adjusted by the computer and the alternator speed will drop and so will output. John

check the connecters, lots of cars that i have worked on actually had rotted connecters on alts.. The alt should put out around 17.5 (not sure if thats for all cars), the alt should be able to power all the acc. in your car and still charge your bat..

17.5 if it is full-fielded. above 13 with everything on as jsj said.