replacement cats

[bigjoe]

I failed the sniff test today. My NOx are too high, almost double. I think my cats are bad. The previous owner installed the SHO SHOP y-pipe so I have no idea how old it is. I will see if my cats are rattling when I have time, but until then...where can you get a set of replacement cats for these y-pipes, or do you have to buy the whole thing over again? Are the cats hi-flow because they are special, or are they just bigger around? If they are just bigger, I can find a replacement cat easily. I have to get the car to pass soon, (the terms of my probation say I can have no violation at all and my sticker is out) so any help quickly would be cool.

Thanks,
BIGJOE

 

[Mr Anonymous]

Where you already have the SHO Shop y-pipe, cat replacement should be relatively easy since their pipes are straight-in/straight-out, so any generic aftermarket replacement that's the right size should fit pretty easily. Easiest thing to do would be to call SHO Shop and ask for the specifics on the cats (like tube size, overall length) or just measure yourself when you check them. You can usually find the generics on eBay in the $40-$50 a piece range.

Unless the SHO Shop pipe has more than 100K on it, I would suspect that your high NOx might be from another source. How's the general overall maint. of the engine?

 

[bigjoe]

the car has only 90k on it total, so the cats can't have that much. The motor is in good shape although the 60k hasn't been done. But I think the HCs are way too low to be that kind of stuff. lean burn causes hotter chamber temps and therefore higher NOx (poor main. generally sees high HC). Could a vortec 73mm mass air with the 24lb sample tube cause it to run lean???

BIGJOE

<small>[ April 02, 2003, 01:24 AM: Message edited by: bigjoe ]</small>

 

[sdpatt]

Vacuum leaks are also the cause of high NOx. The non-California 3.0L engines do not have the EGR systems that were added to combat the NOx. This is causing them to have a tougher time meeting the lower NOx numbers unless the engine is in excellent condition. Mine included.

<small>[ April 02, 2003, 07:54 AM: Message edited by: sdpatt ]</small>

 

[Mr Anonymous]

bigjoe:
the car has only 90k on it total, so the cats can't have that much. The motor is in good shape although the 60k hasn't been done. But I think the HCs are way too low to be that kind of stuff. lean burn causes hotter chamber temps and therefore higher NOx (poor main. generally sees high HC). Could a vortec 73mm mass air with the 24lb sample tube cause it to run lean???

BIGJOE

The C&L (aka Vortech) 73mm MAF with the 24lb sample tube will definitely cause a lean mixture. See this thread: http://www.shoforum.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=17;t=004725

I would recommend reinstalling the stock 55mm MAF when you go to have it re-tested. I would even recommend cleaning the MAF sensor elements when you swap the housing, see this article: http://www.gatewaycleanair.com/mechanic/air4_4/dirtymaf.htm (try to get some electrical contact cleaner at Radio Shack, avoid using carb cleaner). In addition to the MAF and checking for vacuum leaks as sdpatt suggested, you should also check for codes to see if there are any sensors indicating an out-of-range condition which might be effecting emissions.

I think with some attention to maintenance you could probably bring it back into emissions compliance. Again, I would tend to doubt the cats would go bad this soon, but it won't hurt to check them for rattles.

 

[bigjoe]

Thanks guys, I forgot about the vac. leaks I'll check it out. I'm tending to agree that the cats are too new, I don't have a stock MAf, but I'll figure somthing out. Thanks for your imput.

BIGJOE