Alan

Matt - you had previously said the large alternator terminal was at 0.24v - that is what I'm referring to - was that a mistake...? because if not - its connected to something other than the battery...

Alan

IndyMatt

Alan sorry for the confusion here is the run down on the knowns:

1. Battery Replaced and is known to be good.
2. Voltage ~12V at Starter
3. Voltage ~12V at Large Terminal on Alternator
4. Voltage ~12V at Small Terminal on Alternator, with Ignition On
5. Voltage ~12V at Jump Post
6. No Low Voltage Light On When Car Is On or in Test Mode
7. Small Wire Terminal Grounded Out and Low Voltage Light Comes On
8. Alternator Tested Good at Two Shops, Putting Out Around 14V.

So there are the knowns of the equation, the unknown is why the alternator puts out 14V on the bench but doesn't do crap on the car. I have no freaking clue! I'm lost on this one.

docmirror

I'm not too trusting of the connection through to the exciter circuit. Alan's test usually finds faults in that circuit but not always.

If you have some speaker wire sitting around do this:

Connect one end of the speaker wire(fairly heavy gauge) to the small post of the alternator. You can wrap it around the terminal and use a nut, or use a good alligator clip. Put red lead of your meter on the jump block in the right front of the engine bay, black lead to ground. Start the car, note the voltage. Connect the other end of the speaker wire to the jump lug. Watch the voltage of the meter. It should go from 11/12-ish volts right up to 13-ish volts right away. If not, rev the engine quickly for a few seconds and monitor the voltage on the meter.

Report back.

Alan

This is not correct...

With the ignition on but car not running - this should be <1v not 12v

Only with the car running should this voltage rise to 12-14v (depending on the alternator output).

That this wire is at this high a voltage would explain why the charge light does not come on on the dashboard in bulb test mode...

This still appears to be an alternator issue. They need to test the Exciter Circuit (61) function something is not right with it.

A new regulator & brushes would typically fix this... I don't understand why they wouldn't have seen this - unless they just tested it at speed without conecting the 61 terminal...?

Alan

IndyMatt

Alan this the small terminal disconnected with the ignition on. As for the alternator testing, I think the only think they did was test for voltage output at speed. Meaning they connected the positive and ground spun the alternator and it puts out 14V. That's it as far as I know. I am really really suspecting that it has to be the alternator. Something is up with it.


With that said, would a HO alternator be a good option? I will be running a 320 RMS amp and sub and want the charging system to be able to keep up. Basically I have a 20 year old alternator and it wouldn't necessarily be a bad idea to get a new alternator. Basically I can get the 115A Bosch Unit or go for something in the 180-220 amp output level.

ew928

Did they load test the alternator? Does the current alternator put out close to 100+ amps.
My old alternator was putting out about 60 amps.
Would work Ok in low load conditions but wilted when the AC and headlights were on.
The rear defroster+headlights+AC would bring it to it's knees.

IndyMatt

EW, that is what I am worried about, I don't want the lights to dim and such when the AC and or lights are on.

ew928

Saw a cigarette lighter voltage meter (LED voltage display) at Walmart ages ago and bought it for fun.
Turned out to be a great quick and dirty diagnostic tool. Measure it against a trusty DVM to see how far it is off, and then plug into cigarette lighter and run though the usual gamut of electric loading tests.

A/C on off. Headlights (hi beams + fogs).
Test at idle and at around 3,000 revs.

Something like this unit:
Cigarette lighter voltage meter

Not the most accurate to measure from cigarette lighter socket, but give a rough idea if the electrical system is failing.
Little bit more accurate than the dash voltage meter, I think.

Got so tired of electrical issues that I now run my Passport 8500 radar detector in voltage display mode.
When there's no alerts, it shows the voltage it's seeing from the cig. lighter power supply.

IndyMatt

Not from what I gathered, just spun it and measured the voltage output.

WallyP

It appears that there are two main possibilities here:
- A fault in the exciter circuit.
- Two faulty alternators.

docmirror's test will tell you quickly if the alternator works on the car.

The exciter circuit has a LOT of connections to go bad. The most common problems appear to be the blue wire in the #1 connector in the 14-pole connector near the jump start terminal, and the connectors in the instrument pod.

IndyMatt

One alternator tested twice. Both times it put out 14 volts.

IndyMatt

I plan on running his test this afternoon. Putting on that damn alternator again!

Alan

Wally - I agree and its normally well worth checking - however if grounding the exiter wire at the alternator causes the charge light to come on we can conclude the circuit integrity all the way back to the pod is OK.

If the charge light does not normally come on when in bulb test mode with (61) wire connected to the alternator - then we can also conclude that for some reason the alternator is not providing a ground path through the rotor coil when not yet generating... this is a problem - without this current path there will be no field excitation.

I think its pretty conclusively the alternator here. if the only test they did was a no load high rpm voltage test without checking low RPM initiation - it was completely meaningless for this faiulure mode.

It could possibly detect bad OP diodes (esp. w/ scope) or faulty regulator set point but not much else... in summary it was an insufficient (crappy) test to do - Especially so on a retest !

Always go somewhere that really knows what they are doing - Pep Boys/Checker/Autozone/Kragen type stores are not it - unless you just get really lucky.

Alan

docmirror

Alan, the only reason I brought it up is the inrush on the exciter line. I wasn't trying to undercut your analysis. I expect it'll fail again, but the test doesn't take much time.

WallyP

If the parallel resistor has failed or is disconnected, the light will burn, but there probably won't be sufficient power to excite the alternator.

If there is a high-resistance connection in the circuit, it might be possible for the light to burn, but there might not be enough power to excite the alternator.

The full-power exciter test is cheap, easy to do, and splits the possible problem tree in half instantly.

In addition, he has tried two different alternators, with the same results on both - makes the exciter circuit more suspect to me.

Agreed that the problem could still be in the alternator, and I certainly agree that the next step should be to take the alternator to someone who knows what they are doing. It is always a good thing to find a good auto electric shop in your area, and make friends with them. They can check the alternator, rebuild it, and can often even easily and cheaply increase the max output of the alternator.