Silverado sound system help

rockhardchevy · April 11, 2005

Allright first time poster, just getting started. I have my subs and amp in my truck. I'm running the amp off a distribution block (also have a smaller one for 6x9's), and i have a digital readout cap too. My whole system, no matter how loud i had it would get quieter and start crackling before, and the voltage, according to the readout, would drop from the normal 14 or so, to 8, and the cap would start beeping. It did this whenever i turned it on, so i pulled the fuse. So, i redid my speaker wire, and it works pretty good, except, when i apply the brakes moderately, or hard, the subs and 6x9's loose volume, and start crackling before, but as soon as i let up on the brakes, they run great. Anyone know why, or how to fix it? Also, my 6x9's crackle when i turn it up, and my subs are pounding, but they are only 2 months old, so they can't be blown (i think). Grounds are all tight, fuses good, everything seems allright. Thanks, i appreciate all the help i get!

masterp2 · April 12, 2005

Sounds like it's time for the alternator upgrade. Looking at the year of your truck, I think soon it will be history anyway.

Yes, that's why you are getting 8V at idle, you are demanding too much. Brake lights go on, zapping the overhead. That amp is pulling 20-40 amps if you have it cranked. A 90 amp alt, several years old, at idle, maybe delivers 40 (for the whole car).

That's my vote. You could replace the battery with a yellow top, battery may be on last legs too.

Wingnut · April 12, 2005

Hey, welcome to the forums

It sounds more like a problem with the trucks electrical system, not the stereos.

You might want to consider a bigger alternator, and perhaps a second battery.

Just curious, but where in the heck did you squeeze 6 x 9s in there?

masterp2 · April 12, 2005

finally I beat someone.

rockhardchevy · April 12, 2005

Thanks for the advice so far...

Well, i just put a new alternator in a month ago, stock sized though, with a lifetime warranty too. The battery is old though, i may swap it.

I've had this whole system in my old 92 Grand Prix since october, and i transferred it into my new Silverado about 2 months ago. It worked great till about a week ago, when it started acting up. Grrr!

One more thing i noticed when i was driving to work today... The voltage drops only when the truck is driving, and i hit the brakes to slow it down. Not when i'm just idleing, and hit them. It also is only dropping voltage to the subs, cause my cap readout drops, but my guage on my dash is still good.

O and my 6x9's are mounted in boxes on my rear seat right now, but soon i'm going to cut a hole in the side panel itself through the exhisting speaker grilles in the rear, and mount them onto it, and take the 4x6's in the rear out. Seen it done like that a few times.

masterp2 · April 12, 2005

Start at the system roots. Measure the voltage across the battery with and w/o brakes on. Perhaps you have a short with the brake harness that is draining the system. Disconnect the 6x9's and repeat, are they possibly faulty and drawing down the amp, etc. You can figure it out.

But my bet is still on the alternator, even moreso since you said it was new. We never pay attention to capacity when replacing parts, and frequently the cheapest option is worse than the core. Also, if new (rebuilt more likely) it will sink or swim in the first few weeks. Check what capacity it was, then call GM with your VIN to see what the truck came with.

Keep in mind, if you just replace the battery, everything may seem "fixed" while the fresh battery will mask the problem for awhile, until the battery can't take the constant charge cycling any longer.

As for the problem at speed only ??????????? Sorry, can't think of why.

Can you duplicate the problem at idle when you throw all lights/ accessories on?

dbcomm · April 12, 2005

Had almost the exact problem in my Tahoe last year. Everything worked fine until I would come to a stop sign, or occasionally at idle. I would notice my voltmeter at 14-16 volts while driving, and then while stopped it would intermittently drop to 10-12. You could be experiencing the same thing. Try "two-footing it". Take it on the freeway and apply the brake slightly while keeping a steady speed. See if the same thing happens. If it does, I'd say short in the brake circuit (or worse). If the voltage stays steady, check out what my problem was:

It turned out there was a lot of carbon buildup in the throttle body. Took it in, had it cleaned out, and it cleared up all the electrical problems I was having. I now take it in every 15k for the same service.

masterp2 · April 12, 2005

It turned out there was a lot of carbon buildup in the throttle body.

That makes no sense to me ????? please explain the relationship between electrical performance and carbon in the HP tract.

Wingnut · April 12, 2005

finally I beat someone.

<{POST_SNAPBACK}>

At least we agreed this time.

April 12, 2005

I'm running the amp off a distribution block (also have a smaller one for 6x9's), and i have a digital readout cap too.
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More info please;

I'm concerned about the "distribution block" comment.

Did you run an amp power cable direct to the battery or pull it off something already in the truck?

Are the 4x6's and 6x9's powered from the amp or the head? If they are off the head you may want to consider running a better power cable for the head.

At any speed other than an idle a stock system should power an 1800W amp just fine. If not (and assuming you are direct to the battery) you have either a battery or an alternator issue, either of which should show up in the charge meter.

JMHO

dbcomm · April 12, 2005

It turned out there was a lot of carbon buildup in the throttle body.

That makes no sense to me ????? please explain the relationship between electrical performance and carbon in the HP tract.

<{POST_SNAPBACK}>

Basically, what I was told, is that when the buildup reaches a certain level, the the computer (erroneously) tells the engine to idle at a lower lower RPM, and it had a DRAMATIC effect on my overall vehicle voltage. I thought it was the typical dealer BS, but it was under warranty at the time so I had them perform the service. My voltage problems were gone. No more headlights dimming at the stop sign, or other oddities. There are several bulletins regarding this on the web.

rockhardchevy · April 12, 2005

I am running a 4 guage directly off the battery, and have a distribution block, with 2 8 guage outputs. I am running only the 6x9's off the small amp, the 4x6's are run off the headunit.

O and i ran it out on the highway, and when i give it gas, and put on the brake at the same time, it doesn't cut the system out, its only when i let off the gas, and apply a descent amount of brake, and like dbcomm said, sometimes at idle.

I might check with the local mechanic about this throttle body buildup thing.

masterp2 · April 12, 2005

The alt absolutely should provide enough juice for the lowest idle speed the vehicle will ever see. many vehicles have stock alts that barely keep up with the stock truck. Add a bunch of load to it, and you have a power deficit, pretty simple. It's not the battery. Even with a shot battery, the charging system runs the vehicles electrical system

The simplest start is checking the charging voltage. You evidently don't have enough juice. It happens to a lot of people who accessorize or undersize there charging capacity.

Pull off the alt, take it to checker and have them load it. They have a nice little machine that will tell you all about the alt performance...

You have to start somewhere...by getting dirty. Since you have already confessed that the system is under voltage, your problem sounds classic. Most stuff needs 9-11 volts to run properly, it is damaging your stuff to run less than 11V.

BTW, I have a harley dresser that does exactly the same thing you describe. The radio cuts out when I hit the brakes, YOU HAVE AN ALT ISSUE! Get more capacity.

mmmikkke · April 12, 2005

I'd check to see if somehow your body-to-frame ground is corroded or disconnected, and the way to do this would be to wire a volt meter up with one lead going to a body ground (like your amplifier's ground), and the other wire going to a frame ground (run a special wire out the window and to a bolt on the frame, or to the negative terminal on your battery). If you ever see voltage between the two, that would explain the problem.

The instrument cluster is probably wired to a frame ground, and that would explain why it doesn't see the voltage sag. But your brake lights, and the audio system amplifiers probably are wired to a body ground. A weak or corroded body to frame ground strap, coupled with the increased load of having the brake lights on, coupled with the body moving slightly on the frame when braking, might cause the problem.

masterp2 · April 12, 2005

Are you saying your dash gauge doesn't drop below 12V at idle??????????

This is frustrating. Shut off the motor and stereo. Guage reading? Turn on ignition and all lights, what does the gauge read? Turn off lights. Start motor. What is new gauge reading. Turn on stereo, motor running. Reading? Crank stereo. Reading? Now step on brakes. Reading?

The answers will define your problem.