Alternator problem, Low voltage, please check my work

[Who]

Alternator problem, Low voltage, please check my work. Saturday morning I go to start the car and I get a sluggish start. I'm on my way to make an errand so I stop by the auto parts store to check the battery. They check the battery in the car with a black box of sorts and they report that the battery is good but it has a low charge and the alternator failed the test. I go home and pull up the TSRM and grab my digital voltmeter. I don't have a ammeter that goes over 10amps so I could not test the output in amps. Belts are tight, no slipping and the contacts on the battery are all clean and tight. All measurements were done at the B terminal on the alternator. Load measurements were done with the high beams on and high heater fan. I checked the dash light and the light does work.

1. Hot engine @ idle 13.29v, 2000rpm 13.8v
2. Hot engine with load, idle 12.29v, 2000rpm 13.35v
3. Grounded the IC at terminal F per the tsrm, idle 13.4v, 2000rpm 13.85
4. 12.16v volts at the battery engine off.

Monday morning stone cold engine and I used a AC digital probe thermometer to roughly measure the casing on the alternator.

1. Cold start, idle, 14.5v
2. 2000 rpm, 14.7v
3. Alternator getting hotter @ 145F, idle, 14.0v

Drove to work hot and humid at 8:00am. Got to love FL.

1. Arrived at work, alt temp 185F, idle no load, 13.8v
2. Arrived at work, alt temp 185F with load 12.5v
3. alt temp 185F, no load @ 2000rpm 13.8v
4. alt temp 185F with load, 2000rpm, 13.8v

Lunch time stone cold engine.

1. 14.5v at idle no load
2. 13.7v idle with load
3. 12.5 volts at the battery with the engine off.

According to the tsrm. If I bypass the IC regulator and your V readings are "less than standard" the alternator is at fault not the IC. My readings are border line. At cold temps my alternator seems OK but as the underhood temps rise and the alternator gets hot my volt readings start to drop near the low side of specs.

My diagnosis... Failing alternator......Maybe? No starting issues for two days now.

Opinions please.

 

[radiod]

My suggestion would be to find an inductive clamp and test the amperage coming out of the alternator, but my guess is it is on it's way out.

 

[figgie]

and it makes sense. If one of the diodes is intermittent or temp sensitive, as it gets hotter, the readings will change.

Before I keep on.

Very nicely done on the troubleshooting. Very thorough and detailed

Change the IC regulators on the ALT. It will fix your problem. That and they are not that expensive.

 

[Who]

Thank you.

I figured it wasn't the IC regulator. Reason being the tsrm tells you to ground out the IC and if the voltage goes up the IC is bad. In my case the readings stayed about the same. I figured that when you ground out the IC the alternator goes "all out" and maxes out the voltage.

On the other hand ...."The devil knows more because he's old (experienced) than because he's the devil." ...Just to verify by IC regulator I need what Napa calls the Voltage Regulator. For example Napa ECHVR572

 

[figgie]

Who

ouch. Sorry about tgat. Not sure why I called it the IC regulator. Lol. Yes the voltage regulator which is that picture you attached.

One thing I forgot to ask you. What type of load is the alternator reading on the sense circuit?

 

[Who]

figgie

Unfortunately I do not have a ammeter large enough. My digital meter only goes up to 10 amps.
I figured I would have to remove the alternator regardless so I put a wrench on the alternator pivot nut last night. As usual the nut wouldn't budge. I soaked it with some liquid wrench but no success. If it wasn't so close to the wiring harness I would heat it up with a torch but it looks risky. I just want to make sure the bolt does not have a reverse thread for some odd reason.

 

[jdub]

Remove the lower bracket bolt and try to pivot the alternator. That might break it free.

 

[3p141592654]

It does look like a weak alternator. Could be worn out brushes which is a cheap fix.

Where is your ground probe connected when you are making these measurements?

You should measure the voltage drop across the major cables in the the charging system to rule out high resistance in any of the 20 year old connections, including the alternator case to the engine bracket (which is made through the pivot mount) and the engine ground straps.

 

[Who]

Remove the lower bracket bolt and try to pivot the alternator. That might break it free.

You were right. I removed the lower bracket bolt and had to use two hands and quite a lot of torque to move the alternator up and down a few times. I put the wrench on it and the nut came loose easily.

It does look like a weak alternator. Could be worn out brushes which is a cheap fix.

Where is your ground probe connected when you are making these measurements?

You should measure the voltage drop across the major cables in the the charging system to rule out high resistance in any of the 20 year old connections, including the alternator case to the engine bracket (which is made through the pivot mount) and the engine ground straps.

I see your point. I measured the alternator all week hot and cold at several different points. Battery, intake manifold, pivot bracket, ground strap and the measurements were within 0.01 of each other.

 

[Who]

Well I measured the alternator output all week. Stone cold in the morning, 14.5 volts. Hot after coming home from work, 13.8V. Car started fine all week and battery is up to 12.75 volts. I removed the alternator this morning and went to the auto parts store. They put it on the testing machine and it passed all the test even under load. The battery tested fine as well. I wish I could of brought the alternator in and tested it hot after a long drive but that would probably be overkill. If its not broken don't fix it they say.

Any suggestion on what to check or replace in that general area while I have the alternator out of the car, vacuum hoses and such, would be appreciated.

 

[jetjock]

I see your point. I measured the alternator all week hot and cold at several different points. Battery, intake manifold, pivot bracket, ground strap and the measurements were within 0.01 of each other.

I'm gonna guess you did that by measuring voltages across positive and negative points and comparing them. If so that's not what 3p is talking about. Drop testing involves measuring across two points in the same side of the circuit path while the path is under load. It's one of the most valuable electrical troubleshooting techniques a person can learn. Fwiw I have yet to see one of these cars where resistance in the starting/charging system was low enough to meet acceptable levels. All required work to get it there.

 

[Who]

^ You guessed right.... Drop volt testing what is that?... I looked it up and I found a lesson on youtube and here as well. Never knew about drop volt testing or how to do it. Noob in training here. Thanks for the info.

http://www.youtube.com/watch?v=v0THDAS1nws

 

[jetjock]

Nice to see someone who takes info and runs with it rather than wanting their hand held. Someone who understands the internet is more than a global pornography network. A Floridian no less. I'm impressed. If only everyone here was the same. Congrats on learning something valuable. Now you too can be amused by those who feel compelled to do the starter relay mod...

 

[Who]

Took a reading on the battery before installing it back in the car and it had dropped to 12.20V overnight just sitting in the back of my Exploder. I got my battery replaced yesterday... Free! Hope that solves the mystery or at least eliminates one possibility.

On a side note there are a bundle of wires that run behind the alternator and under the intake manifold. I touched the plastic loom protecting the wires and it fell apart into pieces. Twenty years and heat does quite a number on plastic. Back to the auto parts store again for some split wire loom. Another possible headache avoided.

Thanks for the help.