Car wobbles when accelerating

Greetings everyone!

So I just received my 2015 Mustang GT PP back from the dealership after a wheel alignment, all new spark plugs and most importantly, my motor replaced (old one had a cylinder 8 misfire with no recourse of fixing).

Strangely enough, the car “wobbles” when accelerating at high speeds and RPM’s. For example, on the highway when I accelerate under high speeds and RPM’s the car has a slight left to right “wobble.” It feels like the car might fishtail until I let go of the throttle which then starts stabilizing the car. I was wondering if the dealership possibly installed the engine mounts incorrectly (Engine has strut bar), or if there’s any other input or advice someone can point me towards.

Additional Info

-Wheel Alignment was completed at dealership

- Car was moderately rear ended causing uneven tailpipes (passenger side hangs lower, but it doesn’t fluctuate or move around)

- Had a serious car accident (hit and run) a few months ago and had the entire suspension replaced, but never had any issues until now

-Tires have low tread but not low enough to destabilize a vehicle like that

What you are describing, sounds very similiar to what a buddy had going on with his gt350 w/IRS. He had a bad rear wheel bearing. It had a lot of play.

Take the car back to the dealership ASAP and describe your symptoms. If it wasn't displaying these behaviors before something was likely left loose; is misaligned or incorrectly installed. Maybe a combination. Either way, get it back to them and have it fixed right this time. Once repaired, test drive before you accept it.

Additionally, tires can be a major issue. Had a shop put a tire on backwards which led to all kinds of handling issues. Noticed it when I took a closer look at the treads. Took them back and had them remount them correctly, problem solved.

DieHarder said:

Take the car back to the dealership ASAP and describe your symptoms. If it wasn't displaying these behaviors before something was likely left loose; is misaligned or incorrectly installed. Maybe a combination. Either way, get it back to them and have it fixed right this time. Once repaired, test drive before you accept it.

Additionally, tires can be a major issue. Had a shop put a tire on backwards which led to all kinds of handling issues. Noticed it when I took a closer look at the treads. Took them back and had them remount them correctly, problem solved.

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^^^ this right here! I had my tires rotated and balanced, and they decided to do the cross rotations on unidirectional tires. The two front ones were backwards and it wandered all over the place. I’m not sure what effect that would have on the rear tires…


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DieHarder said:

Take the car back to the dealership ASAP and describe your symptoms. If it wasn't displaying these behaviors before something was likely left loose; is misaligned or incorrectly installed. Maybe a combination. Either way, get it back to them and have it fixed right this time. Once repaired, test drive before you accept it.

Additionally, tires can be a major issue. Had a shop put a tire on backwards which led to all kinds of handling issues. Noticed it when I took a closer look at the treads. Took them back and had them remount them correctly, problem solved.

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Thanks for all the input guys and taking your time to help me out. So I took it to the dealership, they checked the suspension, motor mounts, wheel alignment etc… and apparently everything is in tact.

I’m posting a picture of the dealer’s diagnoses to gather more input from you guys along with a picture of my rear end collision that made my tailpipes uneven (perhaps the wobbling is caused by the asymmetrical thrust from the exhaust?)

Strangely enough, they test drove it and “found nothing wrong” so I insisted on taking a technician on a drive with me to illustrate the obvious wobbling effect that occurs during high RPM acceleration. Tech said the exhaust was a possibility, but that the wobbling might be occurring because the new motor needs to “open up” still. Does that even make any sense?

Aside from the visual, the exhaust would not cause that. But, maybe you want to get a bit more descriptive of this "wobble".
Is it wandering, vibrating, shaking, or is it something maybe the fly by wire throttle is doing?

Juice said:

Aside from the visual, the exhaust would not cause that. But, maybe you want to get a bit more descriptive of this "wobble".
Is it wandering, vibrating, shaking, or is it something maybe the fly by wire throttle is doing?

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I guess the best way to describe it would be as follows…

When driving you expect the vehicle to remain stable and steady. Now consider how driving the vehicle in a straight line maintains stability and steadiness without any “swaying” or “wobbling” whilst maintaining an accurate responsiveness to the steering wheel. Moreover, with proper wheel alignment and an evenly paved road you could even let go of the steering wheel and the car would still generally follow a steady forward direct momentum.

Consider that description as I attempt to define what I describe as this “wobbling” or “swaying” effect. Imagine the same situation, with all the same exact variables as above except it happens to be an extremely windy day. As you drive in a steady straight line and let go of the steering wheel the wind blows strong enough to effect the vehicles trajectory. It’s that similar type of “swaying” I’m encountering when full throttle accelerating at any gear over 3 at high RPMs. I’d be on the highway, for example, have the car in 3rd gear, hit the gas full throttle and as the car picks up torque and speed it’s as if the car is suddenly being hit with an extraordinarily strong wind that “sways,” “wobbles,” or “veers” the car left and right like a very windy day. Subsequently shifting to 4th gear maintains this “wobble/swaying” effect so long as the speed is high enough but the steering wheel remains completely UNAFFECTED.

I hope the wind analogy helps because I honestly cannot decipher how dangerous this can possibly be. Full throttle makes it feel like I’m suddenly driving through a wind storm

Have a friend video the effect from a follow car.
As u describe it, sounds like car is struggling for traction and the rear moves around

How bad was the rear of the car from the accident? Any pictures? Any picture of the final Alignment Specs?

86GT351 said:

How bad was the rear of the car from the accident? Any pictures? Any picture of the final Alignment Specs?

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I posted a picture of the accident further up in the thread. But here is the before and after alignment specs. Also, why does it say “except performance, track package” I have the performance pack

They could have tried to move the Rear Camber a little more. Yes it's green, however ideal would be -1.5. Negative Camber indicate that wheel at the top is leaning further in than ideal.

86GT351 said:

They could have tried to move the Rear Camber a little more. Yes it's green, however ideal would be -1.5. Negative Camber indicate that wheel at the top is leaning further in than ideal.

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Any recommendation for what I should do?

Those alignment specs even before aligment do not support what you are describing.
What happens if you hold the steering wheel straight, and accel/decel like get on and off the throttle? If doing that makes the car 'steer' with the throttle, you have a lose suspension part in the rear. You should not be able to feel any play.
I would also jack up the rear wheels, and grab the tire at 3 & 9 o'clock, and 12 & 6 o'clock position and see if there is any play in the rear bearings/hubs.
There has to be something lose IMO.

What he said! LOL!

Juice said:

Those alignment specs even before aligment do not support what you are describing.
What happens if you hold the steering wheel straight, and accel/decel like get on and off the throttle? If doing that makes the car 'steer' with the throttle, you have a lose suspension part in the rear. You should not be able to feel any play.
I would also jack up the rear wheels, and grab the tire at 3 & 9 o'clock, and 12 & 6 o'clock position and see if there is any play in the rear bearings/hubs.
There has to be something lose IMO.

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I do hold the steering wheel and experience this “wind” effect. The dealership checked all suspension parts and the wheels and had the car jacked up. They said there was nothing wrong. However, prior to bringing my car in for a motor replacement, they also did a wheel alignment and the car had this problem the very day I picked up from the dealership. Then I brought it back down the next day and explained the issue, they double checked everything and had no explanation for it

I got no other suggestions man, sorry.

Juice said:

I got no other suggestions man, sorry.

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On the alignment spec sheet it says “except performance, track package” but I actually have the performance pack suspension. Do you think that might play a role in this problem? Perhaps they aligned the car in accordance with the regular suspension GT?

Nikotopless said:

On the alignment spec sheet it says “except performance, track package” but I actually have the performance pack suspension. Do you think that might play a role in this problem? Perhaps they aligned the car in accordance with the regular suspension GT?

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I would need to see both specs side by side.
But in general, NO. Alignment issue would behave the same all the time. Camber mismatch from side to side would cause a pull. I seriously doubt you could feel anything from rear camber being out of spec. Unless its out bad, and yours was not that bad.
Toe out may feel like the car is wandering. That is why factory specs some toe-in.
Specs IMO are just guidelines. More negative camber will improve lateral grip, to a point.
I go by tire wear for small tweaks to my alignment after setting the negative camber I want. Tweak toe to help tire wear of slicks on track. And just run it on the street like that.

You keep going back to the same place. I'd try a different shop, preferably one run by a mechanic. Have them check everything over, including the alignment. You must really trust that dealership to take their word that everything is fine.

13v6 said:

You keep going back to the same place. I'd try a different shop, preferably one run by a mechanic. Have them check everything over, including the alignment. You must really trust that dealership to take their word that everything is fine.

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They’re a legit dealership and replaced my entire motor for free so I hope they’d do their job fine. I just don’t understand how this happened right after a supposed wheel alignment was conducted