Alternator acting crazy

[Josephus]

Hey guys, first post.

I'm helping a buddy fix his '89 Ranger. 2.9V6

It was obviously not charging the battery, so we pulled the alternator and took it up to Advance to bench test it. it tested good.

Btw, we determined it was the alternator because the battery reads 12.6V with engine off and 12.3V with engine running.

So I put it back on the truck to try a few more tests. I decide to use the haynes manual tests to try to find the problem. These tests are very similar to the tests in the Tech Article on this site.

The manual indicates that I should do the S/I Circuit test based on previous test results. (will post if necessary)

This test is pretty convoluted with all the jumpers you have to add in. One of which is jumping the "F" post to the alternator housing.

At some point I have to turn on the engine to idle, and now the belt is SQUEELING. First time that's happened and I took it as a good sign. Volts across battery is around 13.3

I cut the engine, tighten the belt, remove all the jumpers, and restart the engine. Volts across battery are back down to 12.3

I started thinking about the "F" jumper. I reinstall it with the engine running, the RPMs go way down to a true idle and now voltage across the battery is up to 14.5V

When I reinstalled the jumper, it was only temporarily with the engine running. Just a second or two. Once the engine idled down (i'm thinking because of the alternator load) I removed the jumper and the voltage stayed high and the rpms stayed low.

So what is going on with this "F" post? Any alternator experts out there?

Also, the voltmeter in the instrument panel reads NOTHING. I'm going to try to trace the continuity while this post bakes.

Thanks in advance,
J

 

[AllanD]

The "post" that you jumper to ground is supposed to "full field" the alternator, bsically bypassing the regulators control and forcing the alternator to it's maximum output.

Alternators aren't "rocket science"

With the engine running set your digital multimeter to AC volts range (yes, really)
and measure the voltage across the battery... If there is more than 0.15AC volts that is a cause for concern.

If the AC volts is greater than 0.3 volts replace it.

But to me the real test would be to take it off the engine and remove all four screws that hold the Voltage regulator to the alternator and actually LOOK at the brushes.

If the brushes are worn down to the hole for the assembly pin you need new brushes.

AD

 

[Josephus]

someone want to tell me why i'm reading 25 VAC? with the engine off? with two different multimeters on two different vehicles?

sheesh.

 

[AllanD]

Either the battery is dead leading to rediculous readings, OR you need to get out your "multimeter adjustment set" which consists of an 18" length of railroad track
and an 8lb sledge hammer.

Unless it is a Fluke or simmons multimeter which in either case it needs to go in for service.

AD

AD

 

[Josephus]

Ok, so just based on what DOES make sense, the F post grounded causes the alternator to come to life. Do you think the regulator is bad? Or could it be some kind of wiring issue?
J

 

[Josephus]

Battery is fine. Truck cranks fast.

Here's another question. How is the "I" terminal used on the alt? Some websites call it the "excitor". Some have it going to "hot in run". The Haynes diagram seems to have it going to a voltmeter and then ground. Is that right?

Thanks,
J

 

[doorgunner]

My '89 I-wire went to the dash Alt. light...the light causes the alternator to get "excited" which makes it put out 13-15 volts...then the light goes out once the alternator puts out the proper voltage...

 

[BRUTUS_T_HOG]

Hey guys, first post.

I'm helping a buddy fix his '89 Ranger. 2.9V6

It was obviously not charging the battery, so we pulled the alternator and took it up to Advance to bench test it. it tested good.

Btw, we determined it was the alternator because the battery reads 12.6V with engine off and 12.3V with engine running.

So I put it back on the truck to try a few more tests. I decide to use the haynes manual tests to try to find the problem. These tests are very similar to the tests in the Tech Article on this site.

The manual indicates that I should do the S/I Circuit test based on previous test results. (will post if necessary)

This test is pretty convoluted with all the jumpers you have to add in. One of which is jumping the "F" post to the alternator housing.

At some point I have to turn on the engine to idle, and now the belt is SQUEELING. First time that's happened and I took it as a good sign. Volts across battery is around 13.3

I cut the engine, tighten the belt, remove all the jumpers, and restart the engine. Volts across battery are back down to 12.3

I started thinking about the "F" jumper. I reinstall it with the engine running, the RPMs go way down to a true idle and now voltage across the battery is up to 14.5V

When I reinstalled the jumper, it was only temporarily with the engine running. Just a second or two. Once the engine idled down (i'm thinking because of the alternator load) I removed the jumper and the voltage stayed high and the rpms stayed low.

So what is going on with this "F" post? Any alternator experts out there?

Also, the voltmeter in the instrument panel reads NOTHING. I'm going to try to trace the continuity while this post bakes.

Thanks in advance,
J

1. At the voltage regulator connector on the alternator, verify the Yellow/White (Y/W) wire maintains full battery voltage with the regulator connected and the engine running. If the voltage drops, locate and repair the voltage drop in the circuit.

2. If the voltage is steady at battery voltage on the Y/W wire, verify with the regulator disconnected and using a Digital Volt-Ohm Meter (DVOM) that the Light Green/Red (LG/R) wire shows battery voltage key on. If the wire does not show battery voltage, check the battery light on the dash to see if it is still on with the alternator disconnected. If so, repair the short to ground in the circuit.

3. If the LG/R wire shows battery voltage as it should with the regulator disconnected, check the White/Black (W/BK) wire from the regulator connector to the main alternator connector to make sure the wire shows good continuity from one end to the other and no continuity to ground with both connectors disconnected.

4. If all wiring is OK, verify all connections to the regulator are good and tight. If the connections are OK, replace the defective alternator and recheck operation.

In my experience is it a loose or corroded terminal in the White/Black wire connector, the fact that the alternator works at the parts store and when full fielded backs up that suspicion

 

[BRUTUS_T_HOG]

http://therangerstation.com/forums/showthread.php?t=114311

 

[doorgunner]

1. At the voltage regulator connector on the alternator, verify the Yellow/White (Y/W) wire maintains full battery voltage with the regulator connected and the engine running. If the voltage drops, locate and repair the voltage drop in the circuit.

2. If the voltage is steady at battery voltage on the Y/W wire, verify with the regulator disconnected and using a Digital Volt-Ohm Meter (DVOM) that the Light Green/Red (LG/R) wire shows battery voltage key on. If the wire does not show battery voltage, check the battery light on the dash to see if it is still on with the alternator disconnected. If so, repair the short to ground in the circuit.

3. If the LG/R wire shows battery voltage as it should with the regulator disconnected, check the White/Black (W/BK) wire from the regulator connector to the main alternator connector to make sure the wire shows good continuity from one end to the other and no continuity to ground with both connectors disconnected.

4. If all wiring is OK, verify all connections to the regulator are good and tight. If the connections are OK, replace the defective alternator and recheck operation.

In my experience is it a loose or corroded terminal in the White/Black wire connector, the fact that the alternator works at the parts store and when full fielded backs up that suspicion

Ahhhhhhhhhhhh....something even I can comprehend!

 

[Will]

If it's a 1989 alternator then stop wasting your time poking at it with probes and overhaul it. It's like trying to discover the exact reason an 87 year-old marathon runner is no longer competitive. Interesting academics but a complete waste of time.

 

[Josephus]

It's a new alt.
Got it working by giving it battery voltage. Now to find a permanent solution...
I put it in series with a 220 ohm resistor to test it. I'm not too keen on just wiring it straight to the batt. Where's the alt light wiring?

J

 

[straycat]

If it's a 1989 alternator then stop wasting your time poking at it with probes and overhaul it. It's like trying to discover the exact reason an 87 year-old marathon runner is no longer competitive. Interesting academics but a complete waste of time.

A stupid waste of time. 2 years ago my wife's Corolla was hard to start one morning. Battery was dragging. I told the with I thought it was the battery (5years old). I took it to my Goodyear shop and they ran a complete free diagnosis on the battery and alternator and told me it was the battery. I bought a new battery and the total time with me driving there....25 min. and $72 for a 5 year battery. No pro-rating either with the new one. It fails, I get a replacement for free. And........ I had a free bagel and a great cup of free coffee. Cain't beat that.

 

[BRUTUS_T_HOG]

It's a new alt.
Got it working by giving it battery voltage. Now to find a permanent solution...
I put it in series with a 220 ohm resistor to test it. I'm not too keen on just wiring it straight to the batt. Where's the alt light wiring?

J

im sure it would be just as much effort to just fix it correctly. where did you have to add battery voltage to get it working?

 

[Will]

It's a new alt.
Got it working by giving it battery voltage. Now to find a permanent solution...
I put it in series with a 220 ohm resistor to test it. I'm not too keen on just wiring it straight to the batt. Where's the alt light wiring?

J

New as in brand new? Or new as in "rebuilt"?

The alternator in my Chevy diesel ran up the white flag. I bought a rebuild from NAPA and installed it. It didn't work. I took the NAPA alternator apart and it was nasty inside. It was really nasty inside. It was nothing more than a used alternator with a half-assed clean and paint on the case.

After a bunch of ugliness, I bought a new Powermaster alternator and it's been a sparkling performer.

I want to describe to you the starting system on a 379cid diesel with 22:1 compression. It's a big heavy motor with a lot of mass to rotate, and rotate against 400psi of cranking pressure. Plus, rotate fast enough so that you actually get to 400psi so the air is hot enough to set the fuel on fire. You have a serious array of cables and a pair of 1000 cranking amp batteries and also glow plugs, which are like 8 toaster ovens, to feed. After it starts the alternator has to thump out the amps to top 2,000 cranking amps back up because you might only be driving a block before you turn it off and do it all again. Some half-assed painted and re-shelved alternator isn't going to cut it. Most of the time when average people replace a part the part wasn't even bad. These low-end "rebuilt" parts bank on that. They do $10 worth of refurbish on every single part and then sell it for $70. On the rare occasion it doesn't work, they give you another shitty part to try. It's no better than taking an alternator off of a car in the junkyard. They should all be in jail.

My point is--is it NEW? Not unless you paid a couple hundred bucks for it.

You are describing a problem, but we don't have physical access to the machine.