irocz_ca

would like to test the alternator while it is still in the car to see whether it is becoming faulty or not. any suggestions? thanks.

VampireHunterC

Drive to Autozone or somewhere and they will test it for free.

17camaro83

start the car and disconnect the battery if the car still runs then the alternator is good if not then start looking for another one.

Danno

If you own a TG and if you don't own an inexpensive digital voltmeter get one. With the engine running at the battery terminals you should have somewhere between 14-16 volts depending on the battery condition. Never run the vehicle with the battery disconnected, it is a very DANGEROUS way to see if the alt has any soup.

17camaro83

I've seen people test the alternator like that but hey, if it's dangerous it's dangerous so scratch what I said

87TA 305TPI

when my alternator went out, to make sure that was my problem i disconnected the battery while it was running and it died out, so you should be able to check it that way

theCure

did you disconnect the negative or positive or both?

Omar

DO NOT DO THAT! You risk frying electronics when you do that.


Besides that, you disconnect the battery, you kill power to the ECM, and the car will die every time, regardless of whether the alternator is good or bad.

The correct way is to take a voltmeter and check for 13.5-14.4 volts while the car is idling, preferably at 1K rpm's.

88TPI406GTA

Omar is the only one that isn't smoking crack here. Use a voltmeter and check the alternator output at 2000 rpm...in most cases, the output at idle is minimal on most cars. The voltage should be between 13.8 and 14.4 volts at about 2000 rpm. Any higher voltage than that and you will cook the battery over time from overcharging. I used to work at an auto parts store and I also have a father who is an EE to verify my info.

The car is not designed to run off of the alternator. It is designed to run off of the battery with the alternator charging the battery. In most cases the amount of power needed to run the car is less than what the alternator is putting out, so no problem.

As for disconnecting the battery and running the car

I once bought a Turbo 350 from a junkyard. The guy went to a stack of transmissions and TASTED the fluid from each one (to determine how burnt the fluid was) to find a good one. This guy was a grizzled biker so I thought it was par for the course.

You tell me, is that the right way to tell if a trans is good or not? No.....

17camaro83

first off crank is good j/k
seriously the only reason you should check the car by disconnecting the battery and letting the car run is if you just hate the car and want bad things to happen to it.... Yes I did mention about disconnecting the battery while the car is running and it figures I wasn't correct on that matter. just wanted to clear things up a bit

Danno

As I dust off my old sheepskin I hesitate to even post this. I too, have seen it done. Most newer alternators have incorporated into the hybrid module regulator a simple resistor bridge along with a zener diode to detect overvoltage conditions i.e., intermittent cables or possibly a battery on it's way out that is developing high internal resistance. The problem with this type of diagnosis is that the moment the battery is lifted off when the alt is running it may or most probably will surge because of lack of a load(battery). This can cause a catastrophic failure of the pass transistor in the regulator module and this will allow the field to run wide open thus generating voltages well beyond the ability of the ECM and related electronic components to handle. The ECM uses the very popular three terminal voltage regulators along with zener diodes to protect from overvoltage but they probably will fail with an alt running at full bore with no load. As I said before the best investment is a decent digital voltmeter. They pay for themselves many times over and eliminate a lot of guesswork when trying to diagnose a problem. I can't emphasize enough the importance of a properly charged and known good battery. With high output alternators the battery is smacked with high current charging until it comes up to terminal voltage and this is very bad for battery life. Many times the charging system is overlooked as a maintenance item, but a healthy battery and good cables are a must. These cars are getting old and they need to be really gone over to insure reliability.

17camaro83

Holy crap, you know alot about this stuff danno, are you like ASE or something?, man that's really really cool.

Danno

17, I hope the moderator doesn't mind but this whole thing brought about some funny memories. That guy who saw it done was me, and it was my car. I was working and going to college at night and my ride at the time was a 65 Chevy Impala SS with a 396 and a powerglide. After work I was heading to school when the old big block cranked slow needing a jump. I stopped at the service guy up the street who did minor things for me because the 18 hour days did not afford me time to do much else. Old Harry had a Sinclair station complete with the dinosuars on the pumps. He looked one year younger than *** and had a pipe in his mouth all the time and when he spoke he would blow all this hot ash out. I told him the problem and he proceeded to get his diagnostic tool out. It was a light bulb attached to a block of wood with two wires with alligator clips attached. I left the car running and he popped the hood and attached the bulb to the battery terminals. He then yanked the carb linkage and the bulb got brighter as it revved. He the yanked off the battery + terminal and wrapped it in a rag, then took off the neg. The car continued to run, he then came out with a new battery and installed it. I got to school late and afterwards I talked to my instructor as we walked to our cars. I told her about why I was late for class and explained about Harry's troubleshooting technique. She abruptly spun around and looked at me like I was nut's. She then proceeded to inform me that although it was not course related I had better give her a good reason why this was not a good idea. The following week she and her husband invited me out for pizza after class and I gave my various reasons which evidently satisfied her. Even got an A in her course. The fact that her and her husband rode motorcycles and we often took Sunday rides together had absolutely NOTHING to do with it. I wonder if old Harry was still around if he would use that old bulb to work on a TG. My backround is in electronics, specifically communications and broadcast. Since cars went to electronic management it was right up my alley. Maybe we should suggest a board for funniest stories, I'll bet it would be a hoot!