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RPM fluctuation due to subs?

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luckyg817

New member
What's up guys. Got an 04 with what I thought was a vac leak somewhere but never really dug into it too much since it was only like a 300-400 rpm fluctuation if that. Well today I actually noticed that it was due to the subs I have in the trunk that makes it fluctuate. Weird huh? Keep in mind that it is by no means a big system. It's one 12 with like a 400 watt amp so it's not very loud, just good enough to get some bass inside the car. I started noticing because I thought I felt a small surge this morning on my way to work. I went home for lunch and tested my theory and what do you know. The fluctuation was in sync with the bass whenever it hit. If I turned the volume down, the fluctuation would stop and as soon as I turned up the bass, the fluctuation started up again. Now like I said, it's a very little fluctuation and nothing to worry about really but just figured i'd ask if anybody else has ever heard of or had this issue before. Everything works and runs fine, voltage is good. Any ideas or suggestions?
 


Even if it was a small fluctuation in voltage it would cause that? Voltage would only drop like .02-.04 whenever the bass would hit last time I checked it out. I figured it would do that if the voltage drop was bigger and would drop to below 12 or something.
 
All of my GP's had a noticable RPM dip at idle if I ran all four power windows up simultaneously

The electric system just isn't all that powerful to begin with. If you want to get serious about sound in these cars, you'll have to contemplate a voltage booster and/or a beefier alternator.
 
I'm not trying to get serious about sound anymore. I kinda lost the want to have my bass blaring. I'm good with what I have now, just wanted a little bit of insight but i'll check my ground to the amp. I think I used a bolt to the backseat but didn't sand the area down or anything so it probably is power related like billboost said. I'll check that on Saturday though.
 
sorry but it has nothing to do with grounds/power its your alternator trying to make power it doesnt have, so. think of your alt like a big magnet, the more power you try and draw the stronger the field is gunna become, i do competitions and im running 2400rms or 4800 watts with 3 batteries on 2 12's, i had a 275 amp alternator on a 4 cylinder car lol. when the bass hit it dropped 300 everytime because the load on that alternator and that was with 3 runs of power and 4 runs of ground under the hood from alt to front battery, so a simple way to free up voltage is called a "big 3" so run a 1/0 from batt positive to alternator positive, then a ground from the battery to the frame, and a ground from the engine to the frame, use 1/0 for all of it and it frees up alot of voltage, normally you will see headlight dimming before you see rpm drop that hard on a bass hit with that small of an amplifier, any questions feel free to ask :)
 


You say it's not power/ground related and tell her to do the big three. That's a power/ground upgrade. If she turns off the sound system and the car doesn't do it.. she should check grounds/battery connections etc.

If you tell her to check wheel bearings...I'm going to laugh.
 
well if you want to get technical yes it is power and ground related, not them being loose, but the power and ground not being big enough to support what little load is on it, you have to remember alternators are meant to just put out enough power to supply what the car needs, even a small amp like 400 watts will be too much, a capacitor ( even though they are junk) should help her rpm issue, if not then do the big 3, or get an extra battery.
 
and yes bill if she shuts the system off it wont do it, hell if i turned mine down it stopped, and i had plenty of voltage on tap, i was idleing at 15.8v and if i was at a red light and hit a low note id sometimes see 11v and thats with 3 batteries, a 275 amp alternator, and 4 runs of wire
 
And yet.. I run an amp of much more power w/o the big 3 and without issues on a 125amp alt.

As the cars age, ground and power connections become corroded etc. The side terminal connections from the battery are notorious for corrosion. I have fixed a P0171 Lean Bank One by replacing battery cables on a car w/o any sound equipment modifications. Things like this are why I suggested checking those connections. Checking is totally free, takes a few minutes and a set of eyes.
 
Whoa whoa whoa. I don't know where yall got that I was a chick from but i'm a guy. Haha. Just wanna clarify that real quick before anything else.

Trett93 I see what you're saying but the alternator is brand new and the voltage isn't a huge drop when the bass hits. The lights do dim very little, barely noticeable but I do think it might be the ground to the amp. I'll try that first and if it still continues, i'll ask questions.

Billboost, now that you mention it, I think my wheel bearings might be a little loose. You think that could be the problem?......;)
 


Haha. How dare you??? It's all good man. Yea I was reading and I was like whoa, hold on, stop it. Stop it dammit! All good tho.
 
yes corrosion is a big factor, and doesnt matter if the alt is new, they really arent meant for any extra power besides what comes from the factory, but go ahead and start with power/ground cleanup. ill just sit here and wait :P
 


i dont know much about building l67's or supercharged motors but old 350's and stereo equipment, now youre talking my language ;)
 
Doesn't really have much to do with building the cars. It's more them getting older. If you remove the bolt from a battery cable and slide the boot up, a lot of times you find a fuzzy green corroded cable causing issues. Resistance, bad grounding etc etc.

We will both sit and wait, based on his comment about checking the ground at the amp....I'm thinking he's aware that the ground isn't as good as it should be.
 
lol yeah especially a seat bolt, its a good ground if clean, i used to use the child seat bolt on the top of the trunk in my old sunfire lol, and i can build an l67 but when it comes to what springs/injectors/rockers im pretty well clueless, and its been a while since i installed a cam so cant remember how to do the rocker tightening sequence, dad says just get em snug and run it with open valve covers and tighten as needed lol seems sketchy, and there isnt much space on the back head between my firewall
 
I don't think It's about ur subs drawing to much power at all I have 2 10s with a 900 watt amp and my system just barley makes the power in the car fluctuate so I'd say look through your wiring to see if one of the wires is starting to corrode also clean off the wire going into the alternator I constantly do that with mine as well as the ones going into the battery but again if it's power related u can always wait till night to do the test and turn on ur head lights and see if there is any fluctuate in power
 
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