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Discussion Starter #1
So ive been having some trouble for quite some time.

Bad MPG - 11 city 13 highway cruising at 65

running rich - bullydog shows 12.5 at cold idle, warm idle, and through most of the powerband

Then one day on the highway I gave it a little gas to pass someone. All of a sudden i lose all power and car starts shaking a whole lot. I had to get it towed home. I took the cats off and this is what i saw. Also a pic of my spark plugs to help diagnose.

After gutting the cats all seems to be well but im still running rich and no codes are thrown?? Should i do idle relearn, idle air, and ecu reset?

Also what are some suggestions to help with backpressure to get back some torque. hiflo cats welded in place of the primary gutted cats? or resonator before of after the flowaster.



 

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Discussion Starter #3
volant intake. airflow snorkel. IMS. flowmaster. bullydog is set to stock right now and it has a narrowband sensor. dont exactly know what the difference is but i know wide is better.
 

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Wow !!!! I am not a certified mechanic but I would do an oil change asap to remove any particles that might have been sucked into your engine. How many miles on your truck, how long have you had bad mpg?
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Discussion Starter #5
oil change needed to be done anyway so that was done today as well. im only at 77k... the mpg is hard to tell since it got bad. with front and rear bumper + winch, sliders, full skids, lights, snorkel. there is bound to be a decrease in gas milage. if i could just get 15 going 65........
 

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I don't mean to hijack but I have a question - I've heard a couple stories about this happening without any codes thrown beforehand and doing serious hell to the engine. I have 100k on my X and don't know if the cats are original. Are these something that should be changed preemptively before any codes are even thrown?

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Thats messed up luck, lol. Knock on wood.....
I mean I've replaced several engines for customers, not on my own rig. Usually cats break down after an owner drives around for weeks, months, sometimes years with a check engine light on and fuel trim maxed out just destroying their cats. Often a person has it coming to them, after refusing to do some basic repairs. Sort of a pay a little now, or a lot later karma type things. Not saying this is always this case, just more often than not.
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You're gonna wanna pull your resonator pipes off too and tap them clean. When the cat breaks apart, it packs the resonator full of crap.
 

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Discussion Starter #16
You're gonna wanna pull your resonator pipes off too and tap them clean. When the cat breaks apart, it packs the resonator full of crap.
By resonator do you mean the secondary cats or the resonator after the muffler. The secondary cats are hollowed out not too and after the flowmaster is a dump before the rear axle.



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I've replaced several engines because of it. See it quite a bit working as a tech. Hell, it happened to a guy on here a month or so ago.
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I'm breaking in my new engine as we speak. Had no codes thrown, just a buzzing noise that in hindsight must have been the cat fragmenting, though at the time I thought it was just another noise from the failing motor mounts.

Cat let loose at 75mph and motor was shaking and lurching as I pulled it over. Replaced the cats, ran it for another year but the rings were torched.

Now with rebuilt motor, warranty, and DT long tube headers to prevent this type of failure again..or so I told my wife.
 

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Discussion Starter #19
Since I've gutted them I get a slight increase in mpg. I ordered some magnaflow universal cats and plan to weld those in to create some more back pressure. May get a a new magnaflow muffler and y pipe and go stainless all the way from headers back.


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