hello all... fisheye here... couple of months ago i had the resonator on my car deleted.. then i put a magnaflow on there and noticed immediately loss in power. i assumed it was the resonator, being that there is less back pressure in the exhaust now that it is removed... couple weeks later my CEL came on... it was the ECT sensor. replaced it and code went away but the code still comes on when i drive late at night on the freeway on a cold cold night... the coolant temp gauge stays on cold when im driving fast on the freeway on cold nights but when i exit and drive in city it warms up again and i guess the ecm is blaming the coolant temp sensor... couple weeks after that i noticed a loud noise that sounded like an exhaust leak... after all these problems occured i decided its time to put the resonator back... so today i finally had the time to put the resonator back and had the "exhaust leak" checked out... turns out that exhaust leak is actually a shattered catalytic converter. F*CK MY LIFE!!
so now that the resonator is back i still do not feel any power gain... i still feel like the car has lost some power... could it be the shattered cat? is it dangerous to drive like that? will i pass smog? any advice is appreciated thanks!! oh and btw the exhaust guy said it'll be $280 to replace 1 cat parts and labor... is that cheap??

-Fish

 

Sounds like classic failing-thermostat behavior. Replace the thermostat and you should be good-to-go. Should get your power back too (cold engine = reduced power).
BTW the ECU has no way to blame the thermostat, since this behavior is only reported by the ECT.

 

thanks man i kinda suspected the thermostat as being the problem... and i never said the ecm blamed the thermostat.. i said it blamed the coolant temp sensor...

 

so what happen to your cat it crack? like the shell? or the rock inside ?

is it a 1.8t? i well take ur cat if u dont need it i need to make a test pipe ahaha

 

everyone else seems to have the right idea. I wouldnt suspect the resonator/muffler combo for the loss in power. I was running essentially the same setup. mag muffler w/ res delete and there was a small loss in low-end grunt but nothing to write home about. there wasnt much of a change at all aside from the noise.

 

Just for the record, I hit a rock with my 93 B4 years ago. CAT rattled for a while till it overheated and the CAT goodies melted into a ball and blew back into the muffler. At that point, I had very little power, and not only had to buy a CAT but a muffler too.

If you really think the CAT is bad, so something about it.

 

New thermostat and a test pipe

 

sorry for the super late response... i been busy at work...

so i finally got the cat replaced... the rattling noise is gone... but i still have that loss in power that im worried about... im pretty sure all i need to do is slap the stock muffler back on and get rid of the magnaflow... but i dont wanna give up the magnaflow because it just looks so good on the car... kinda sucks having a v6 12v cuz theres literally no performance upgrade out there that i know of thats bolt on or legit... :'(