Vehicle Jerk to Subwoofer Beat While Acceleratng

I have a 2011 Range Rover Supercharged (full size) and for like 5-6 years I didn't have any problems but now when I am accelerating, the vehicle slightly jerks when the subwoofer hits. If I am driving at a constant speed, you can feel the vehicle lose some power as if you let off the gas and on again very quick or quickly tapped the brake; you can also see the bump in the RPM on the gauge as well. When climbing a hill, it is very noticeable too.

We first thought it was an old battery problem and replaced the battery; that didn't help. Next, we found out the alternator had issues and that was replaced with a new one; that didn't help with the jerking.

I am about to purchase a new capacitor, likley a 3 farad and installing that to see if it gets better.

Does anyone have any idea where the problem might be?

The set up is as follows:

2 Alpine Type X suboofers
2 Alpine PDXM12 1200W amplifiers
1 Farad Pheonix Gold Capacitor

Thank you.

The vehicle has keyless push start

If you're using a factory alternator (150A), you're trying to use more power than it can provide.

I'm in no way affiliated with this vendor, but here are some available high output alternators:

https://www.qualitypowerauto.com/item_379/Land-Rover-Range-Rover.htm

(never tried them, just found them in a Google search)

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My ex once told me I have a perfect face for radio.

I have considered purchasing a high output alternator but it just doesn’t make sense since everything worked just fine before with the factory alternator and battery for several years..

You have 2 amplifiers that can pull 100 amps a piece, and your factory alternator is only rated at 150 amps.

If you turn off the system and/or remove the main fuse under the hood, does the problem remain? How about at lower volume levels?



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My ex once told me I have a perfect face for radio.

With the sound system switched off or at low volume, it is fine and no jerking or anything

Well, there you go. Until you get a higher output alternator, keep it at lower volumes. You might even consider removing one of the two amps and wiring your two subs in series to alleviate your demand on the alternator.

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My ex once told me I have a perfect face for radio.

As I mentioned before though, I never had any problems with the factory alternator for several years.. I also replaced it with a new factory one recently..

jasdip wrote:

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As I mentioned before though, I never had any problems with the factory alternator for several years.. I also replaced it with a new factory one recently..

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There's your problem. Make sure your belt tensioners are properly installed. Did you do it yourself or have it done? If you had it done, go back to the shop and talk to them.

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Support the12volt.com

Do we even know for sure it is electrical? It could be caused by the vibration of the subs. The only way I see to figure out which is to mount a charged battery and temporarily connect the amplifier power wire to the new battery. You will have to ground the new battery and the only connection to the positive terminal will be the amplifier power wire.

DYohn] wrote:

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jasdip wrote:

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As I mentioned before though, I never had any problems with the factory alternator for several years.. I also replaced it with a new factory one recently..

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There's your problem. Make sure your belt tensioners are properly installed. Did you do it yourself or have it done? If you had it done, go back to the shop and talk to them.

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It was done by the Land Rover dealership, I still have warranty on the truck..

Ok, so I did some testing with a good friend of mine (whose pretty good with sound systems and electrical stuff) and here is what we found:

With the sound system off:

Battery: 14.3v
Amplifiers, capacitor, circuit breaker: about 14v

With sound system on and bass turned to full and volume blasted (lowest values which were hit):

Battery: 13v
Rear Fuse Panel: 11.2v
Amplifiers: under 12v (between 11-12)

We also noticed that the system was installed with a 4 gauge wire which was not even independently run to the battery in the front, it is piggy-backing off the rear fuse box power which also has a 4 gauge running to the battery. When I was at land rover today, the service manager confirmed that everything behind the fuel tank and a lot of stuff related to fuel pumps, injectors, etc. are controlled from that box and it's basically a small computer which also needs power and, as we suspected, that could likely be causing the jerking.. See image: https://www.dropbox.com/s/wwku1vfuj10kdc2/IMG_9160.JPG?dl=0

The service manager did say that people normally run a second battery in those trucks.. and the Bentley's and others come stock with 2 batteries as well and one runs the electronics..

My friend said that he feels that the capacitor is probably shot as well and replacing that with a higher powered one (he suggests 10 or even 20 farad, even though I think a 3 farad would suffice) may help with the issue but recommends also running a 0 gauge power wire to the battery (adding a second battery is ideal of course but that is way too much more work/cost)..

Let me know your thoughts..

Just an update (very late but finally got back to this):

I ran the 1/0 gauge wire directly from the battery to the back and connected it into the capacitor (I replaced the original capacitor a while back with the current one). I tested the sound system and the jerking did not go away. Almost no difference after bypassing the rear fuse box.

Next, I installed a second battery in the back, after fully charging it first. I connected the batteries in parallel (I did not put a fuse/circuit breaker between the back battery and the amps just for testing, but there is one between the first main battery and second). I do notice a decrease in the jerking when the bass hits but it did not go away. It is probably at least half of what it was before the second battery was installed. The bass also seems to be louder/stronger with this set up as well (hopefully its not just in my head).

I am thinking about permanently installing the second battery in the back to lighten the load on the factory electrical system. If I do, should I be adding any solenoid in the setup, or fuse between the second battery and amps, or anything else to ensure proper charging and safety? I don't ever listen to my music without the truck running so I am not worried about draining the battery with the engine off.

Second, since there is still jerking when the bass hits, any idea what the problem could be at this point? Would a high output alternator solve this issue? Would it be able to solve the issue without installing a second battery?

P.S. I am going to disconnect the power wire from the main battery today so I run on the second battery only and see what happens

Another update:

I did some further testing yesterday, I disconnected the main battery from the second battery just to test what would happen with the sound system running from only the second dedicated battery. The result was that the truck was still jerking when the bass hit. The only relation to the truck the sound system has with that set up is that the ground wire on the second battery is still connected to the chassis. The lights still very slightly dim (same as before) as well. Does this change anyone's opinion about the suggestions?

By the way, I also took the power wires out of the amp connectors since they were showing some corrosion. I decided to cut the ends, strip them back, and connect them again. I saw that both the ground and positive wires going into the amps are corroded. They are green around the outside perimeter of the wire. The center in pretty clean. The speaker wire appears to be similar from what i can see through the clear jacket but I haven't taken those apart and stripped them back. These are about 9 years old. I was thinking to replace all of the wiring perhaps and replaced the soldered "Y" connections to the amps with power distribution units while maintaining 4 gauge all over and eliminating the 8 gauge. See image attached of one of the positive 8 gauge wires going into the amp. Could this be causing a problem? The ground wire to the chassis looks good however.

Have you done the “big 3” upgrade or checked your factory grounds up front? You should have a fuse on the 1/0 gage power wire under the hood. From there the 1/0 connects to your capacitor, then splits off to your amplifiers? You should have a 4 ga power and ground wire running to each amp, preferably with a fuse block between the cap and amp.