Perfect fit -- well made, great price
By Jeffrey K on September 16, 2019
I have a 2004 Jeep Wrangler Unlimited with an automatic (LJ, if you will) and the factory cats were shot. It took about 230,000 miles to kill them, so I can't complain. I read various reviews and settled on Flowmaster because of the positive comments, and am very impressed with the construction, quality, and fitment. The upper assembly with the mini-cats bolted into place with absolutely no trouble -- everything lined up perfectly. You'll need new exhaust flange bolts because the stock bolts have too small of a head for the flange holes... that, or get some washers. I used M10x1.5-40mm full-threads with washers and they fit perfectly.. 40mm was just right, but 50mm might be easier and there's room. The Flowmaster exhaust flanges are thick, flat steel so a 17mm hex head fits with no trouble. The stock exhaust flanges have a lip, thus the smaller heads on the stock bolts.
A few hints:
1) Get a can of Liquid Wrench, PB blaster, WD-40... whatever you prefer... and soak the old bolts for a little while. Keep a torch handy and use it if the bolts don't break free. Heat helps significantly.
1) You don't have to completely remove the skid-plate. Simply remove the transmission-to-skid-plate bolts and the skid plate bolts on the passenger side, then loosen the bolts on the drivers side to let the plate hang loose. This will give you plenty of room to access to the rear cat/muffler bolts. Make sure you support the transmission first -- I used a floor jack gently snugged under the driveshaft near the front universal... don't jack up the Jeep -- this isn't jack point, just support the transmission.
2) I was able to remove the stock assembly and install the Flowmaster assembly without removing the front drive-shaft... there is room. It would be easier to reach all the exhaust flange bolts with the front driveshaft removed, but it's not absolutely necessary.
3) While you've got everything removed, take this time to replace the pre-cat O2 sensors on the exhaust manifold -- they're easy to reach with the mini cats out of the way. While you're at it, install new O2 sensors on the mini cat assembly before you bolt it to the engine. I taped the O2 sensors wires to the pipes to keep them out of the way while fitting it to the engine. Spend the money on quality O2 sensors.. I used NGK and have no problems.
4) Loosely bolt the mini cats the to exhaust header -- one person can do it, but an extra set a hands might help. Then slide the rear cat onto the hanger, then slide it onto the mini cats pipe, then loosely bolt the rear cat and muffler together. Now tighten the mini cats assembly to the engine, then tighten the rear cat to the muffler. I have a stock muffler and cat and muffler flanges lines up perfectly.
5) Before you put the skid-plate back, install the exhaust clamp at the rear converter/muffler junction.
It's not a fun job, but it's doable on ramps in the driveway. What made the difference was the exactness of fit ... I didn't have to hammer, bend, twist, or deform anything to get this unit installed -- everything lined up and fit like a glove. Plus, the price was right. I couldn't be happier, and engine power has been restored.
What was in the box:
front assembly with mini-cats, rear cat, an exhaust clamp, and a warranty card.
Things you'll need:
new O2 sensors, sensor-safe anti-seize, new exhaust flange bolts (flange head or use washers), one day, a patient spouse, and several beverages of your choice.
You can't go wrong with these. Good luck!
