Featured Sound system is causing transmission shifting problems.

[bananapehl777]

Hi all,

I am having some issues with transmission in my Subaru, and it's actually been a problem since I've had my audio system installed, I just didn't think it was due to the aftermarket audio system (I replaced valve body and have done countless fluid changes, had it diagnosed by dealers and other shops and they could find nothing wrong with the transmission, put $2k down the drain trying to figure it out). The big issue is that when I am accelerating and moving through the gears (like moving on from a light), the transmission will shift very weird -- like someone who does not know how to shift a manual; it feels like the computer messed up how to shift the gear appropriately and the car bucks. It does this only when I have my system turned on full tilt and playing bass, it will never do it if I have the system turned down or off. I've posted about my setup in the past, from this thread: https://www.caraudio.com/threads/ho-alternator-idle-conundrum.608986/. Everything is still pretty much the same now. Here is a diagram of how the subwoofer amplifier and important electrical wiring is. All electrical connections (grounds, battery conditions) are freshly cleaned, corrosion free, and are stripped of paint. All wires in diagram are 1/0 AWG except for the labeled 4 AWG. Battery voltage can dip into the mid 13s for a very brief moment when engine is revved around 2-3k RPM when bass note starts, then immediately jumps back to above 14 V.

I have set the amplifier gain using the multi-meter method measuring voltage across the subwoofers while playing a 40 Hz test tone (V = sqrt(Power*Resistance) - 34.6 V = sqrt(1200 W * 1 ohm)), so I don't believe I am clipping the signal.

I am at a loss what to do especially since I want to put a bigger system in someday, and it prevents me from really enjoying the system's full capabilities to the point where I don't turn it up at all because I don't want to damage the transmission. I have heard I need a cap or that I should bypass the grounds to the body and instead run dedicated ground wires, yet the car audio shop I go to said not to. I am assuming most people are able to drive their cars normally with these big systems installed playing at full volume and have no drivability issues? What am I missing?

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[dragon.breath 10+ year member]

I would suspect that a wire for the transmission control got disconnected or damaged during the stereo installation. It could even be that a pinched wire is getting vibrated by the subs and is causing the problem.
Without being there when the car is having the problem, I don’t think anyone can be more exact.

 

[Jimi77 Premium Member]

Are you experiencing a voltage drop when the ****** "skips?"

 

[1aespinoza Premium Member]

What am I missing?

You may be having an issue with the ground wire that goes to the ecu or bcm. Re enforcing those may be the answer.

 

[metalheadjoe 10+ year member]

I suspect it's an ignition problem rather than a transmission problem.
Start with the basics: plugs, wires, coils, check engine codes.

Does the problem change depending on how hard you accelerate?

 

[Roy Gallimore]

Did you ever find the issue I’m having the same thing going on my buddy that owns the audio shop said it could be the battery. Since I’m using so much more power the alternator could be overworking to “pump more juice” if you will because I feel it only happens when I’m driving with the bass.

 

[Cee]

Did you ever find the issue I’m having the same thing going on my buddy that owns the audio shop said it could be the battery. Since I’m using so much more power the alternator could be overworking to “pump more juice” if you will because I feel it only happens when I’m driving with the bass.

LOL January? Ya this OP isn't replying back. So many incomplete threads on forums with posters who never reply back with a conclusion. Good luck.

 

[bananapehl777]

Did you ever find the issue I’m having the same thing going on my buddy that owns the audio shop said it could be the battery. Since I’m using so much more power the alternator could be overworking to “pump more juice” if you will because I feel it only happens when I’m driving with the bass.

 

[bananapehl777]

So far, after installing a dedicated 0 AWG OFC ground from the front to the rear battery, and grounding my subwoofer amp to directly to the rear battery (using 4 AWG, that's all the amp will accept) I have not had an issue with the transmission shifting weird. I still want to install a super cap at some point, but I am happy with results for now.

 

[Jimi77 Premium Member]

I was thinking Big 3....

 

[Old_Slapper]

Like Jimi77 said, I was just about to ask if you did the big-3. That would cause that problem.

 

[ThxOne Premium Member]

Ahhhh yes... I had a Jeep Grand Cherokee, 1995 that had this problem. My voltage was dropping into the 9v range on hard sustained bass notes. Jeep would buck and hesitate. Turned the volume down and she was fine. I upgraded the alternator and installed a 10F stinger capacitor and it never did it again. I suspect the alternator was the help I needed. Voltage stayed above 11v after that.

Edit: my 2006 Elantra did this as well but only for the overdrive as the overdrive was electronically activated.

 

[Old_Slapper]

After installed a new sub in my kids ranger and wired it to 1 ohm, the extra power draw would cause my son's engine to die when he cranked it up. I added a 2 awg to the alternator, battery to block, and battery to chassis. Now it stays above 12v. We already installed a 250a alternator about a year ago. I just held off on upgrading the wiring, under the hood, because I was too lazy.

 

[bananapehl777]

Like Jimi77 said, I was just about to ask if you did the big-3. That would cause that problem.

I was thinking Big 3....

Big 3 was done when I first got the system installed.

I would like to report that the dedicated ground between the two batteries did not fully help the issue. The voltage was still very easy to drop during any bass note if played at full volume. This is was observed by the fact that all lights in the car would literally "strobe" to the bass notes. My Accessport also would easily see voltages dipping down to the high 12s for split seconds even if my engine speed was >1500 RPM. It was my hunch that these system voltage fluctuations, caused by that current hungry sub amp, were messing with the automatic transmission shifting as I mentioned originally. Because again, they never happened if music wasn't loud.

I did solve this issue permanently though. Two weeks ago I installed an XS Power SB650 super cap bank in place of the rear D3400, right near the sub amp. This cap can easily give the amp the current it needs as quick as it needs it, so system voltage remains very steady. IT MADE A WOLRD OF DIFFERENCE. No more strobing headlights, no more transmission issues when stopping or going from a light, voltage on my Accessport never dips below 13.8, and it doesn't even fluctuate much at all when heavy, separate bass notes are played. I finally have confidence in my electrical system after like 6 years of having it.

Next project is sound treatment with Resonix, which is proving to be quite the task . Hence why I have not put too much effort into the wiring organization back there, everything will be coming out.

 

[Jimi77 Premium Member]

Big 3 was done when I first got the system installed.

I would like to report that the dedicated ground between the two batteries did not fully help the issue. The voltage was still very easy to drop during any bass note if played at full volume. This is was observed by the fact that all lights in the car would literally "strobe" to the bass notes. My Accessport also would easily see voltages dipping down to the high 12s for split seconds even if my engine speed was >1500 RPM. It was my hunch that these system voltage fluctuations, caused by that current hungry sub amp, were messing with the automatic transmission shifting as I mentioned originally. Because again, they never happened if music wasn't loud.

I did solve this issue permanently though. Two weeks ago I installed an XS Power SB650 super cap bank in place of the rear D3400, right near the sub amp. This cap can easily give the amp the current it needs as quick as it needs it, so system voltage remains very steady. IT MADE A WOLRD OF DIFFERENCE. No more strobing headlights, no more transmission issues when stopping or going from a light, voltage on my Accessport never dips below 13.8, and it doesn't even fluctuate much at all when heavy, separate bass notes are played. I have finally have confidence in my electrical system after like 6 years of having it.

View attachment 70699

Next project is sound treatment with Resonix, which is proving to be quite the task . Hence why I have not put too much effort into the wiring organization back there, everything will be coming out.

Congrats. That was a tough problem to figure out. Luckily the solution was easy enough.