I don’t know why, but my YJ specifically has always been a pain when it comes to aftermarket stuff fitting properly. There is ALWAYS some snag. In this case, I am talking about the exhaust.
The history of my exhaust is as follows:
- July 2013 - Bought the YJ, with all factory original exhaust. Catalytic converter was rattling (internals break up and then shake around, supposedly common). No loss of performance or anything, just noisy.
- November 2013 - I go out of town for a week on a trip with my mom, and my dad takes the YJ to a local shop and has them replace the cat. Does this as a surprise/gift. I come home to a quiet YJ.
- A week later I notice a weird startup rattle, only when starting the engine. It seemed to be in the cat area and so I took it back to the shop. They said they removed a dust shield or something. I am not sure how a cat has a dust shield (or why it wasn’t removed upon install originally), but that’s what they said. Noise solved.
- April 2014 - factory muffler starts rattling. Not sure why, but it sounded really bad and obnoxious. I couldn’t really see the issue but I suspect the heat shield strapped on top probably was loose and rattling.
- May 2014 - install a flow master 44 muffler and walker tailpipe. Terrible sound, super loud and awful. I couldn’t get the muffler to crimp to the pipe (broke several clamps), so the tailpipe would rattle around. Just horrible.
- August 2015 - got sick and tired of the flow master, so I ordered a Dynomax muffler and tailpipe kit. This one fit pretty good, although sometimes the tall tailpipe hump would rattle against the tub.
- January 2017 - the Dynomax has a raspy sound…turns out the front pipe that connects to the cat broke off of the front of the muffler completely. Kept riding it like this (barely ever drove it) until March 2019.
- March 2019 - installed Magnaflow cat & cat back. It fit mediocrely, it was a pain to get just right, but I got it and I don’t recall it hitting the tailpipe hanger. Didn’t hit the tub or anything else, either.
- I don’t remember why or when but eventually I took the exhaust apart, and put it back together, and on the magnaflow tailpipe, the piece of metal that hangs the tailpipe started hitting the hanger bracket bolted to the frame. Essentially a symptom of the kit being installed too far rearward, because the hanger piece is welded in front of the factory tailpipe hanger bracket on the frame.
- October 2022 - tried a borla kit with magnaflow cat, wouldn’t fit. Trimmed the cat, still wouldn’t fit. Tailpipe hits the fuel tank front frame crossmember. Returned kit. Reinstalled magnaflow that still hits hanger.
- 2024 - tried all walker cat, muffler, and tailpipe. Tailpipe hits tub like the old Dynomax kit did (same parent brand). Took back apart to reinstall magnaflow, ruined all the Walker stuff trying to get it apart (crimped together)
- It’s 2025 now - annoyed with Magnaflow hitting the hanger bracket, so I ordered another borla to try again. WTF - still a problem.
So there are basically 3 components to this problem.
1. The muffler has an enlarged pipe to slide over the cat exit pipe. This means that the muffler bottoms out on the cat pipe. This could be a good thing.
2. The tailpipe has some bends in it that are supposed to put the pipe in the right spot.
3. The tip goes on the tailpipe and is what hangs in the hanger. The tip looks obviously wrong when it’s installed not straight up and down, so you ideally want to get it perfectly straight.
So for the problems. First, you install the muffler onto the cat and it slides on as far as it will go. Right off the bat, this puts the whole kit too far back. The tailpipe will not go on without jamming straight into the frame crossmember for the front of the fuel tank. No matter what you do to the tailpipe (which way you rotate it), it will not work right.
So the solution to that so you can begin to go in the right direction is to trim the cat exit pipe. I measured from the cat body to where the Borla pipe stopped initially (1”) , and cut off that same inch from the end of the cat exit pipe.
Slid the borla back on, and it bottomed out on the cat body. Good. This means it’s as far as it can reasonably go. The only way to go further would be to trim the cat exit more and then also trim the borla entrance some, which I don’t want to do.
Even with this trimming, the tailpipe doesn’t f’ing fit. I can force it to kinda fit, but I have to turn the muffler off of level, I have to really put force into the pipe away from the frame (and clamp it that way), and then even once I’ve done that, the tip still really does not want to sit straight. If I try to turn it straight, it forces the tailpipe back into the frame.
So WTF? What gives? What am I doing wrong? Is aftermarket stuff really just this bad of a fit? There is no reason why my YJ should have this much trouble with this. I’m using stock style engine/trans mounts, I have a stock tub, stock frame, stock hangers. I just don’t understand why I have an issue.
I fired up the engine with the borla stuff in place and go figure, I love the way it sounds. Sounds much quieter and refined than the Magnaflow. I’m tempted to put the Magnaflow back on anyways, because I bet with the 1” trimmed off the cat, I can probably get the muffler on enough to avoid the tailpipe squeak. However, I don’t really want to run the MF because it’s loud and annoying. But maybe it’s my short term solution.
I am tempted to make my long term solution be to install the borla (crappily) and then take it to a muffler shop and tell them to rework the pipe until it fits and don’t quit until it’s done.
I don’t know what else to do. I’m tired of the exhaust either being too loud, rattling, breaking, or just plain fitting so poorly that I can’t install it to begin with. I don’t understand why I have issues and I just want them solved.
I have found a factory 2.5L muffler/tailpipe brand new, but with it being a different part number, I don’t know if it would fit properly. I do know that the borla advertises itself as 4.0L fitment only, so there should be zero excuse for it not fitting.
Pictures for funsies.
