Been noticing lately my 97 mark 8 has been losing power gradually and found some posts about a rotten egg smell and clogged cat at wot, sure enough tested it out last night and after red lining it at wot got that nasty smell so looks like my 3rd cat is clogged, my question is what's the best way to resolve this ? I figure a 2.5" xpipe is one way or just two 2.5" test pipes will fit in place of the 3rd cat? Power difference between those 2 resolutions? Got test pipes already so thinking of trying that if not maybe ordering a cheap xpipe off ebay, How concerned should I be about the 2 near the manifold too?
3rd cat clogged
- Thread starter mmikeman
- Start date
I would figure out WHY they are producing the sulfur smell/getting clogged. The smell doesn't necessarily mean they are clogged.
It's due to your engine pumping unburned fuel through them that is producing the smell.
For me the problem was a stuck IMRC plate on drivers side.
Figure out why you're running rich is my suggestion and solve that issue, then do the test pipe if you so desire.
It's due to your engine pumping unburned fuel through them that is producing the smell.
For me the problem was a stuck IMRC plate on drivers side.
Figure out why you're running rich is my suggestion and solve that issue, then do the test pipe if you so desire.
87TTOPGT420
Dedicated LVC Member
Same issue, cat was plugging up had cat removed added universal hpipe car had much more response
ford nut
Local nut case
If they stick it should throw a code with no ce light.
Check codes.
Yep, my regular ELM327 wouldn't pick up the stuck IMRC code.
My SCT X3 found it though.
Lownslowlsc
Dedicated LVC Member
A stinky third cat isn't all that uncommon. I've had a stinky #3 since I bought the car, only happens sometimes at wot and at 65mph+. It runs great and gets the mileage it's supposed to.
thaywood
Dedicated LVC Member
Cut that 3rd cat off and put an H- or X-Pipe in there. My '97 LSC had a stinky 3rd cat at WOT that drove me nuts. Replaced with an H-Pipe and no more stink. It also felt more powerful and gas mileage improved marginally. Plus I got about $80 bucks for that cat at the scrap metal yard 
My buddy at the shop in town is getting me a good deal we couldn't find an h-pipe for cheap anywhere however picked up two test pipes were going to bend to put in place of the 3rd cat and he's going to hollow out the other two near the headers to be safe, the 2 pipes were only $20 not the best way to go but def cheapest, I'll post results my only fear really is that I might need o2 sims if I set off a check engine light somehow, I got the LSC so looks like true dual exhaust straight back, if we can find some magnaflows I may throw them on too
Work got done today , noticed no more smell better response with 3 rd cat gone, then my buddy decided to hollow out the other 2 to avoid problems down the road...noticed decreased gas mileage in town slightly better mileage on high way back to same power I started with, probably will need the o2 sensor simulators I suspect its running lean from no cats
The rear O2's only tell you whether the cats are functioning properly.
Your front sensors are what communicate with the PCM to adjust runtime parameters and have nothing to do with the cats.
ford nut
Local nut case
What would the symptoms be of a stuck IMRC plate and where is it located?? might have this issue, noticed now after the mod my exhaust is making a strange noise like its clogged or restricted from the tailpipes, I also cleared the code using ODB2 software via android called torque, starting to notice power loss as well and loss of torque off the line I'm thinking maybe the o2's arn't working period for some reason