'96 rodeo alternator woes

[tkw829]

As mentioned in the subject, I have a 1996 rodeo and here is the problem I'm having:

I purchased an amplifier, stereo and speakers to redo the stock sound system. Everything pretty much works fine except when I do a sudden acceleration of the vehicle. When I do this, the voltage meter drops to around 12V and the amplifier drops the volume of the music(music also becomes distorted temporarily). I have had all the wiring inspected several times over with no problems found. I installed a capacitor with no luck. I replaced the battery with no change in the problem. I had the alternator tested and it passed with flying colors. The only thing I've come across that seems to be related is the behavior of the alternator during sudden acceleration. There is apparently a feature in the rodeo where the computer? drops the voltage output of the alternator during acceleration to reduce load on the system. From what I could find out about this feature, the voltage is not supposed to drop below ~12.8V. My guess is that maybe after all the wear (120,000 miles), the drop is no longer at 12.8V but might be lower. I have no idea how to fix that if that is the problem. Any suggestions would be appreciated.

[2eyefishclaw]

get yourself a capacitor

[tkw829]

already got a capacitor. Unfortunately, it didn't help. I think this is partly because if I suddenly accelerate and the voltage drops, it can take some time for the voltage to go back to 14.4V based upon when I ease of the accelerator pedal. As far as I know the capacitor can only handle brief drops whereas more often than not I see extended drops. Turning on the headlights resolves the problem completely, I just don't care for that solution.

[Ramblin Fever]

I know you said you had your alternator tested, but did you test it under load?

I endured pretty much the same agony all summer long, on my 97 Rodeo, but without the upgrade in stereo system, however, your symptoms mimic the exact symptoms I had. And the end result was a new BOSCH alternator.

My alternator failure was not "obvious", because when tested at Autozone or on my home volt meter, it was totally fine. However, flip on the stereo, A/C, in combination with a green light, and a light foot, and all volts drop to 11-12 for few seconds. While this occured, the A/C would shut off, and stereo would dim.

I lived with this all summer because everything checked out fine, all connections, with the exception of a corroded positive battery cable, which was replaced with no difference in volts, new battery, and even a new "remanufactored" alternator. Turns out that under load, the reman. alternator was not even putting out half of what it should.

Funny thing was, like you, when I'd turn on the headlights, volts stayed exactly where they should.

I'll tell you these trucks are VERY picky about having a good clear travel of volts, and whenever anything's just a little under par, i.e. battery, alternator, starter, they will sense it sooner then most vehicles. Chances are, when you installed that stereo, your alternator was already on the weak side, now it's probably on it's way out.

Let us know what you find out

[tomlcollins]

2eyed, any ideas on what the connection between the headlights and voltage readings would be? that's kind of crazy...

[tkw829]

Thanks ramblin, I think that's what I needed to hear. I've spent so much money on batteries and things to improve the connections for the stereo that I was afraid to spend money on anything else and be back at square one. I'm going to get a Bosch alternator at NAPA and report back with what happens. As for the headlight idiosyncrasy, I think when you turn on the lights, it creates a continuous demand and the alternator increases output appropriately. This is a very oversimplified explanation, because I'm technically challenged.

[2eyefishclaw]

stay away from a/m alternators its rare to find a good one

[upallnight]

There is a technical service bulletin issue on this. My Rodeo does the same thing voltage drop during a sudden acceleration, but remain constant if the lights are on. The dealer changed the alternator once and I change the alternator this summer. still having the problem so I drive with the lights on.