SW86 Posted March 12, 2012 Share Posted March 12, 2012 any draw backs? some say you need the back pressure. some say you don't. some say it has nothing to do with back pressure but more of catching extra gases from the motor. either way i don't have emissions down here and I'm sure mine is clogged up after 23 years of use. I'm about to re-route the exhaust and if i can loose it, i will. its mainly a trail rig soooo yeah... thoughts? Link to comment Share on other sites More sharing options...
AMCJeepMJ Posted March 12, 2012 Share Posted March 12, 2012 I bought my MJ with a straight pipe in place of a cat, and it is street legal on my side of the Cascades [no emissions or state inspections (you should see some of the barely-running heaps on the road around here)]. I have never run it with a cat, and do not know the difference in performance. Perhaps someone else can chime in with the pros/cons of running without? Link to comment Share on other sites More sharing options...
dasbulliwagen Posted March 12, 2012 Share Posted March 12, 2012 I have a gutted and sleeved cat on my 2.5 and noticed no loss in torque and maybe a slight pickup in high end power. I need the appearance of a cat in my area, so thats why it is the way it is. I think youll be OK. My boss's 88 4.0 MJ is missing the guts in the cat, and his runs fine as well. Link to comment Share on other sites More sharing options...
Jeep Driver Posted March 12, 2012 Share Posted March 12, 2012 No cat here either. And better for it. Link to comment Share on other sites More sharing options...
btm24 Posted March 12, 2012 Share Posted March 12, 2012 Gutted mine a while ago, runs fine don't think I see any power ganes or any thing but it works Brandon Link to comment Share on other sites More sharing options...
SW86 Posted March 12, 2012 Author Share Posted March 12, 2012 i guess it won't be getting replaced then. Link to comment Share on other sites More sharing options...
carnuck Posted March 12, 2012 Share Posted March 12, 2012 I have a gutted and sleeved cat on my 2.5 and noticed no loss in torque and maybe a slight pickup in high end power. I need the appearance of a cat in my area, so thats why it is the way it is. I think youll be OK. My boss's 88 4.0 MJ is missing the guts in the cat, and his runs fine as well. Same thing on my 4 and 6 cyl rigs. External part is there, but the internals ended up in the old muffler. As long as it's injected and tuned, it passes fine. I've even dialed the fuel back a bit because they wasted up tp 20% of the gas by overfuelling to feed the cat. Wonder where the new cars "suddenly" got a boost in fuel economy? There you have it. Link to comment Share on other sites More sharing options...
nicholasdances Posted March 13, 2012 Share Posted March 13, 2012 Just removed my cat a month ago and put in a glasspacK. Runs better then it did before and sounds great. Haven't noticed any drawbacks yet. Link to comment Share on other sites More sharing options...
Truckcom Posted March 13, 2012 Share Posted March 13, 2012 How do you dial back the amount of fuel ? Link to comment Share on other sites More sharing options...
skidoo_j Posted March 13, 2012 Share Posted March 13, 2012 I have a gutted and sleeved cat on my 2.5 and noticed no loss in torque and maybe a slight pickup in high end power. I need the appearance of a cat in my area, so thats why it is the way it is. I think youll be OK. My boss's 88 4.0 MJ is missing the guts in the cat, and his runs fine as well. Same thing on my 4 and 6 cyl rigs. External part is there, but the internals ended up in the old muffler. As long as it's injected and tuned, it passes fine. I've even dialed the fuel back a bit because they wasted up tp 20% of the gas by overfuelling to feed the cat. Wonder where the new cars "suddenly" got a boost in fuel economy? There you have it. What did you do to Lean it out? Did you alter it on the renix system? Link to comment Share on other sites More sharing options...
carnuck Posted March 16, 2012 Share Posted March 16, 2012 Adjusted the MAP sensor on Renix. Had a buddy with a 3 gas analyzer help me. That should read "Put an adjustable MAP sensor in so I could dial it back. Link to comment Share on other sites More sharing options...
Paul Bruchal Posted March 16, 2012 Share Posted March 16, 2012 Mine was clogged so I gutted it, welded it back on, PASSED Inspection. I THINK I get better MPG with it. Link to comment Share on other sites More sharing options...
Comanche County Posted March 17, 2012 Share Posted March 17, 2012 I would not do this, unless I'm way out in left field here, the engine programming relies on the function of the cat. It will effect the engine's performance in that if there's no functioning cat the fuel mixture will be affected. So get a high flow aftermarket cat or a new stock replacement. Most experienced techs or emissions guys know the sound of a hollow cat anyway and you're risk getting a failure at emissions as well as a potentially poorer running MJ. Contrary to popular belief the engineers who designed our trucks were not stupid and much smarter than most of us "tinkerers". When it comes to the engine monitoring system, don't leave it to chance, stock isn't such a bad thing. Link to comment Share on other sites More sharing options...
dasbulliwagen Posted March 17, 2012 Share Posted March 17, 2012 I would not do this, unless I'm way out in left field here, the engine programming relies on the function of the cat. It will effect the engine's performance in that if there's no functioning cat the fuel mixture will be affected. So get a high flow aftermarket cat or a new stock replacement. Most experienced techs or emissions guys know the sound of a hollow cat anyway and you're risk getting a failure at emissions as well as a potentially poorer running MJ. Contrary to popular belief the engineers who designed our trucks were not stupid and much smarter than most of us "tinkerers". When it comes to the engine monitoring system, don't leave it to chance, stock isn't such a bad thing. I'm not trying to say youre wrong, and I know they were designed a certain way for a reason, but the experience of myself and others shows no loss of performance or reliability doing this. And there isnt an inspection station anywhere that will gamble the cost of inspecting the inside of a cat. Now if our trucks had an after cat monitor, this would be a different story. In that case, having the guts inside is mandatory to keep the CEL off. I know it is better to keep everything intact in most cases, but this isnt one of them. Link to comment Share on other sites More sharing options...
Harley Posted March 17, 2012 Share Posted March 17, 2012 I would not do this, unless I'm way out in left field here, the engine programming relies on the function of the cat. It will effect the engine's performance in that if there's no functioning cat the fuel mixture will be affected. So get a high flow aftermarket cat or a new stock replacement. Most experienced techs or emissions guys know the sound of a hollow cat anyway and you're risk getting a failure at emissions as well as a potentially poorer running MJ. Contrary to popular belief the engineers who designed our trucks were not stupid and much smarter than most of us "tinkerers". When it comes to the engine monitoring system, don't leave it to chance, stock isn't such a bad thing. I'm not trying to say youre wrong, and I know they were designed a certain way for a reason, but the experience of myself and others shows no loss of performance or reliability doing this. And there isnt an inspection station anywhere that will gamble the cost of inspecting the inside of a cat. Now if our trucks had an after cat monitor, this would be a different story. In that case, having the guts inside is mandatory to keep the CEL off. I know it is better to keep everything intact in most cases, but this isnt one of them. :agree: These trucks were designed in a different era. Our systems are alot more simplified than they are nowadays and that's how we can get away without a cat. I have yet to see somebody at a smog station know the sound difference. All they know is what the computer screen tells them, pass or fail. Beyond that they don't know much.....at least from what I've seen in this region anyway. Link to comment Share on other sites More sharing options...
Comanche County Posted March 17, 2012 Share Posted March 17, 2012 You guys might be right, but I think spending the dough for a high flow cat is the better option than drilling or doing without a cat. I don't have emissions testing here so there's no worries, but I wouldn't chance it if I lived in an area that had it. Its also illegal. Its a potential emissions rejection waiting to happen, then you're just left with a headache for a marginal performance gain. Unless its just an off road only rig, then go for it. BTW, :D all you guys are eco-terrorists and you should expect a smelly horde of coffee sipping trustafarians (trust fund babies with dreadlocks) setting up camp in your front yards anytime now, you bunch of dirty polluters.... :thwak: Link to comment Share on other sites More sharing options...
SW86 Posted March 17, 2012 Author Share Posted March 17, 2012 mines an offroad "mainly" rig. random trip to the store happens but I'm not worried. so many guys running without, ill be fine. if any hippies want to show up here, ill pull a cartman and bear mace their asses :D Link to comment Share on other sites More sharing options...
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