[Erikka84]

Hi,
Was wondering what could cause a thump thump type feel when accelerating and feels almost like outta gas unless I lift off gas for a minute. Car also sounded funny in the rear with spongy type brakes before this happened. Brakes no longer spongy or sound from rear since thumping started...help?

 

[Joseph Upson]

Welcome to the forum. A clearly discernible video/audio of the noise, along with a detailed description of the basics of your car, is necessary for anyone to have a reasonable clue, given so many problems can present with that description.

You may also be able to stop by a local shop and find someone that can take just a minute to listen to the car and possibly give you insight as to what the problem may be. If the engine light is on and I'd be surprised if it is not, autozone and advance auto parts will scan the car and give you the codes they find for no charge.

 

[Mullah88]

Does the thumping happen when you let off the gas and the transmission down shifts? And thumps when you step on the gas

Sent from my SM-N920T using Tapatalk

 

[TheFlash]

inspect the drive line for broken bolts or bad U joints. If all is good continue looking for the problem. Take two aspirins and get back to us.

 

[tiernan263]

Hi,
Was wondering what could cause a thump thump type feel when accelerating and feels almost like outta gas unless I lift off gas for a minute. Car also sounded funny in the rear with spongy type brakes before this happened. Brakes no longer spongy or sound from rear since thumping started...help?

 

[tiernan263]

I have the same thing on 2008 CTS 3.6. I have On Star so called them and they quickly tapped in to the car's computer and said that (in my case) #5 plug is misfiring. If you have On Star then you may want to try the same thing.

 

[Joseph Upson]

I have the same thing on 2008 CTS 3.6. I have On Star so called them and they quickly tapped in to the car's computer and said that (in my case) #5 plug is misfiring. If you have On Star then you may want to try the same thing.

Welcome to the forum and very good on that association as I did not associate the thump, thump with the very characteristic persistent cylinder misfire that gives that sensation.