Phatmatt

iTrader: (9)

First I have to say this is getting pretty annoying since I've already replaced the alternator twice and the battery & terminals once.

This has started a couple days ago and I have no 'real' idea what it could be. So I'll be driving and my voltmeter says 14V+ as soon as I hit the brakes to come to a stop at a light or stop the voltage will go down to as low as 12V sometimes lower, as soon as I start moving again it will instantly go back up to 14V+

I don't understand why it does this, it wasn't doing it before and I haven't changed anything to the electrical in the car recently.

Other symptoms I'm getting which I think are related are the radio turning off and back on sometimes repeatedly, hearing the engine noise in the speakers, and lights flickering when I hit the brakes. (all this started at roughly the same time)

I have done some research and found out that it could be a worn out alternator belt slipping? Could this be the problem I've been having making me change the alty twice and batt once? I remember when I got the car the mechanic told me I had to change my alty belt, but when I looked at it, it seemed fine to me. I guess he was right

Anyone have another possible answer to this?

LvR

1. @ Idle and no electrical load - what is the battery voltage? (measure on the battery itself)

2. @idle with lights and fan and hazards on - what is the battery voltage? (measure on the battery itself).

3. Same situation as #2 above but measure the voltage between the thick output wire directly on the alternator and the positive battery terminal (black lead on the alternator terminal and red lead on the battery positive post).

4. Same situation as #3 but with engine @3000rpm

5. Same situation as #4 but measure the voltage between the alternator body and the negative post of the battery.

Come back with those 5 answers and we'll take it further and solve it pronto............

Phatmatt

iTrader: (9)

Ok I've done 1 and 2, about to do the rest.

1. 14.26V
2. started at 12.35V and kept going down, I stopped looking at 12.15V

Phatmatt

iTrader: (9)

3. 12.30V - 12.38V
4. 14.25V - 14.30V
5. 13.98V - 14.05V

LvR

From your answers to 1 and 2 its obvious that the alternator is not charging the battery @idle speed (for whatever reason)...............

#3,4 and 5 would have enabled one to determine if the alternator itself was the problem or if cables/connections were the problem. Unfortunately you have not measured correctly due to either reading/understanding problem or a problem with my description of what to measure, and the actual values you posted there must have been taken incorrectly as they don't make sense on a 12V vehicle

Your volt meter should have a red and a black lead. In my original post I said "(black lead on the alternator terminal and red lead on the battery positive post)." and that is exactly what I meant and what you should be doing ............. if you are doing it right you should measure a reading somewhere under 1V for test #3 and #4.

Thats is probably my fault for being unclear:

What you should be doing is just as in #3, @3000rpm with lights and fan and hazards on, put the black lead on the alternator body and the red lead on the battery negative post and get an answer for #5 - it should be also under 1V.

Phatmatt

iTrader: (9)

right, I did it the way you said first but what I was getting I thought was wrong

here is what i got (what i remember) I'll have to redo those tests tomorrow to be more exact.

3. -0.12V
4. -0.31V
5. didn't do

I did it the other way cause I was getting negative(-) readings.

LvR

OK now we are getting somewhere.

The value for #3 tells you that the alternator is producing some current at idle but obviously not enough to cope with the vehicle's electrical load. The #4 value tells you that the alternator @3000rpm is outputting nearly 3 times the idle output current ................... its also telling you that the fat cable between the alternator and the battery has poor connections/terminals on it as that cable with good clean connectors and terminals should produce #3 and 4 readings of under 0.2V (the "-" doesn't matter just so long as you measure the voltage drop over that cable's ends).

I predict that your alternator body to negative battery post voltage measurement in #5 is going to be in the order of 0.3V too.

All of this leads me to believe you have 2 problems.

1. You have an alternator that is not right for the application or its faulty. If you look in the FSM page EL24 you will find that the alternator should be outputting around 24+ amps at idle - more than enough to keep the battery from discharging at idle (assuming you have no stupid lighting system or suspect non-OEM electrical loads on the vehicle) ................ iow if the alternator is working as per spec, you should be able to continue to measure more than 12.6V on the battery during test #2

2. As a result of the alternator not performing to spec, you may (imo you do) have a damaged battery - since a good part of your driving happens at low revs, that alternator is not able to fully charge the battery and its in fact constantly ensuring that your battery gets close to "flat" every time your motor idles with a lot of electrical load.



I would suggest you get the alternator sorted and conduct the tests I detailed here yourself while the person supplying the alternator is present and have him explain why the alternator is causing the draining of the battery (anytime the battery voltage drops under 12.6V its draining).

I would also suggest you remove the cable between the alternator and the battery and ensure its terminals are clean and in good condition and that the cable itself is in good condition too. The same goes for the earth strap between the alternator body and the engine - you really want those voltage drops on those cables during tests #3,4 and 5 to be as close to 0V as possible.

Phatmatt

iTrader: (9)

Thanks, that really explains a lot of things.
I don't have any crazy lighting or nothing of that sort, The only things I have would be my voltmeter that I installed on the cig lighter circuit, and my fog lights (which hasn't been connected for about 2 months or more)

Yesterday I checked the negative cable from the battery to the engine, and cleaned the connectors on those, as well as both terminals on the battery.

I'll try and check those from the alternator, but those are not fun to get too since they are under the car.

Do you reckon that it could only be the wires? or it's really time to change the alternator and possibly the battery again. Cause I would really want to just clean/replace the wires and the problem go away, but I think it's too late for that.


You have been a lot of help to me, much more than I expected of getting from anyone. I can't thank you enough, we need more people like you!

LvR

IMO its too late - you are going to have to get that alt sorted (and make sure you personally do those measurements to confirm adequacy rather than relying on the supplier to screw you over again).

IMO you are going to need a new battery - if not now then in the near future.

The cables will not solve your problem - its basically good preventive maintenance practice only and will ensure your alt and batt last as long as possible.