I usually come to this forum about my Bronco. But when I saw this section it reminded me of a problem I have been having lately with my Mustang. It's not a truck but just pretend for a moment.
Well I have been having problems with the radio cutting off at idle. It also does it when I hit the power windows or wipers or any extra load. I have a Kenwood CD reciever, 2 Alpine amps (20x2 RMS) a Kenwood (50x2 RMS) and an electronic x-over.
These were never a problem before with the stock alternator but I have since added a Holley electric fuel pump, and a Crane ignition system. I can easily tell that the pump puts a major load on the electrical sys. The alternator is a heavy duty model, part of GT package but I think it is only about 75-85 amps. Do I need to upgrade? The battery is a new Interstate Megatron with 1000 ca's and 90 reserve minutes(an awesome battery in my opinion). Do I just have something wired wrong? I've been doing stereos for ten years now and I haven't seen anything like this.
Oh! One other thing. that Kenwood amp seems to cut out when I turn it up.(the volume). I have it pushing two JBL 8's. I consider this to be a simple job for the amp, but when I turn it up some on a heavier song it starts to cut out on the bass notes. Is that clipping? I have a 7 gauge cable powering it, is that too small? Any ideas I would appreciate cuz it drives me nuts!
Thanks
Brandon

 

Brandon, When you say the radio cuts off at idle, so you just lose sound, or does the radio power off? If it does this everytime you hit the power windows or anything electric, I am unsure as to why it would do this. I have seen things run much slower and quieter due to having too much electrical drain on the battery and alternator. Are you amps all fed seperatley or do they share the 7 gauge power wire? Did you jump the remote wire to all three amps, or did you run it through a relay first? I have run across you problem with the clipping before. Many thngs can cause it. Check your grounds. MAke sure they are in excellent condition. Are you running this amp bridged? I have run acroos the problem when bridging amps too low that they heat up to fast, then shut down, and instantly start back up again. Don't know if any of this is going ot help you or not.

Good Luck

Murph

 

Hi
I would also pop out your subs and just make sure your positive and negative speakers leads are not touching . Also are your amps bolted directly to the floor or something else metal that is in direct contact with the frame because this can cause a ground loop.
tonka

 

that alt should be a 100 amp unit, plenty for what you have IMO, as far as the deck i would say lose wire as your not running out of power since you have that also awesome to me megatron with plenty of reserve at idle, and the amp 50x2 ? what eights ? i think the amp is shutting down its just working TOO HARD imo

 

Does it happen at speed, or just at idle? If it's just at idle, you can have your alternator pully replaced with a smaller diameter set. If it happens when the engine is at speed, you have problem with current drain! I would suspect the electric fuel pump, since it didn't do it before.

 

It only happens at idle. I can hit the gas and it will come back on. The whole thing cuts off like it has lost all power. i think the amps stay on but not the radio. I haven't even had the alternator checked yet. Could it just be a bad diode? It seems to charge the battery ok. The radio just turns off when it idles. Especially when the lights are on. Evne in the daytime, if I let it idle for long enough, without touching the windows or anything, it will start to blink on and off. I may have the alternator checked first and then I may check into the smaller pulley. Where would I find one or who makes them?
Thanks for all your help so far!

Brandon

 

You could just check with your local outo parts store for a larger aftermarket alternator. Or you could go online to Jegs (www.jegs.com), or Summit (www.summitracing.com) both these places sell larger aftermarket alternators.

Good Luck

Murph

 

do you have a voltmeter? what is it reading if you do? I tkae it since you haven't mentioned it, you don't have "power pulleys" on your 'stang, but I know mine create the same problem. At idle the alternator doesn't produce the same amount of amps as it does at peak output, remember it's a product of a reciprocating assembly. 100 amps maybe at 3000 engine RPM, but idle is considerably lower. The site below (from Powermaster) has a little table at the bottom that helps figure amp load. they've got some other stuff you might wanna look at too.

http://www.powermastermotorsports.com/Racing/Delco_Late_Style/Which_Alternator_Do_I_Need_/which_alternator_do_i_need_.html

1989 F-150 : 5.0, shorty headers, Flowmaster cat-back, K&N filtercharger intake, March pulleys, "Multi-brand" performance ignition, soon to be Mass-Air...doesn't know she's not a Mustang

 

The best solution is to have your stock alternator pullies replaced with smaller ones. If you go to a high power alternator, you might still have the problem since any alternator, at idle, will only put out "so much" power. If it's spinning faster at idle (smaller pully set), you should be fine.

P.S. Yes, I have had this same problem. I replaced alt. with a 125 amp, aftermarket unit. Same problem! had a set of small pullies installed on my old alt. and re-installed it for a test, and yes, it's still on there. Sold the expensive high amp unit.

 

I also have the same problem. The smaller pulleys make sense but I do have one question. At high RPM's will the extra speed on the alt cause any damage?

 

Ok, here is your problem. A car audio reciever has a typical operating range of 11-14 volts. When your running your vehicle with all of the extra and aftermarket electronic devices, the alternator is not able to keep the battery at a constant 12v. When it dips below 11v or so, the radio cuts out. This would be at idle when your vehicle is not spinning the alternator very fast. The solution would be to get a higher output alternator installed. As far as the amps and subs go, the 50X2 amp should be ok for two 8" subs - IF you dont have the gain turned all the way up. If the bass sounds too punchy, or weaker at lower frequencies, then a more powerful amp would be in order. The 7awg wire should be fine for the amps you currently run. If you get a larger amp however, you will need a thicker gauge wire.
Hope this helps!

-Wiggs