So I regret that my first as second post on this new account have to be trouble shooting threads alas...

So, yesterday I had the stock muffler on my XJ replaced with the same form factor version of the Flowmaster Super 44. Sounded really good up until I drove 2 hours on the highway today. Once I reach what I believe is 4th gear (low rpm, high torque) the engine starts to rumble and vibrate the jeep. The exhaust also sounds like it's fluttering.

I've read that a leaky exhaust can cause a lack of back pressure which in turn then causes the engine to "stumble" When you accelerate at these low rpms, it's not like the acceleration I used to get and the engine and exhaust flutter in sync. When I floor the petal,however, and it downshifts back into a high rpm low torque acceleration, the sound and ride are both smooth like normal.

When I got off the highway the exhaust started to sound almost straight pipped. Now it's like twice as loud idling. From what I can see at a glance none of the welds are broken but is that a possibility? Am I just overreacting to new muffler symptoms? Is it just a bad exhaust configuration? Anyone have any ideas? I have knowledge but no experience with exhausts. Like I said all the pipes are the same size and same inlet and output location. I will post in a little bit if the cold start sounds normal, until then any help is appreciated!

 

Check the exhaust header, it may have cracked open which is a common thing and make sure the downpipe isn't busted either.

What year is the Jeep?

 

You installed a loud muffler, and you're surprised it's loud?

 

The jeep is a '98 and as far as i can inspect neither of these are busted. Thanks for the suggestion though!

Not quite, I actually like the loudness. I'm just worried about the vibrations, its not a subtle one, its more like a wobble but up and down instead of side to side. I only mentioned it sounding straight pipped because before the 2 hour drive, it didn't sound like that.

Its still vibrating after about 250 miles of highway driving. Although it may be getting better, I can't really tell. Could this be due to the lack of buildup in the new muffler?

 

I would assume the new muffler should tone down after a while due to carbon build up, but the vibrations, maybe a loose shakle?
Back pressure isnt much of an issue, I run straight pipes and I dont have that :/

 

I have the same muffler. around 1500rpm the frequency just likes to resonate the whole truck, there not much you can do. Look all the way down the pipe and make sure all the hangars are good and its not contacting anywhere.

 

Hmmm thanks for the replies. Hopefully it'll work itself out in the next couple of days. The vibration isn't so much of a sound vibration like what you're talking about sounds like. It's more so almost like one of the tires is off balance or something. It's low frequency, probably about 8-10hz, and pretty aggressive (my seat squeaks from the movement and the steering wheel seems to vibrate the most noticeably.