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After Market #1/Pre cat for a 98 Gen 2.5? #1043075
03/02/12 12:21 AM
03/02/12 12:21 AM
OneTime  Offline OP
Joined: Feb 2008
Posts: 120
Phoenix, AZ
My truck is throwing P0421 code that has been ruled out to the pre cat. My mechanic ( a new guy I took it to) said that any aftermarket cats will probably throw a code again and that I need to go with a OEM cat. The dealer wants 700 and aftermarket cats go for about 250. Any thoughts? Brand suggestions. I can live with CEL light if I can just gewt it pass emmsions. AZ emmisions will fail you with a CEL light on,

edit: I have been looking on line for parts and a confused. Are there two cats up front on the Gen 2.5 a left and a right?

Last edited by OneTime; 03/02/12 06:16 AM.

98 Gen 2.5 w/ winter package & 31x10 BFG ATs.
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Re: After Market #1/Pre cat for a 98 Gen 2.5? [Re: OneTime] #1043076
03/02/12 09:06 PM
03/02/12 09:06 PM
TOASTY  Offline
Trail Leader
Joined: Jan 2002
Posts: 6,127
Mesa AZ, US. *****
i have aftermarket cats and have no issues, running Magnaflow high flow units x2 total. They're about $80 each.

1999 Montero Blizzard package

1991 Montero RS
Re: After Market #1/Pre cat for a 98 Gen 2.5? [Re: TOASTY] #1043077
03/03/12 01:31 AM
03/03/12 01:31 AM
fasteddy  Offline
Web Wheeler
Joined: Jan 2001
Posts: 13,649
Helen , GA *****
Have the ohtwo sensors on that bank tested first. P0421 is set when the precat and post cat ohtwo's have a too similar reading, indicating the cat is not doin' it's job. The precat sees a LOT of heat because of where it is, and may have failed, and may not have. I've seen this fixed with a 18mm thread plug fouling thingy from the Help section of the auto parts. It's just an internal and external threaded fitting that goes into the cat bung and then the cat goes into the fitting.

Not responsible for advice not taken...
Re: After Market #1/Pre cat for a 98 Gen 2.5? [Re: OneTime] #1043078
03/03/12 03:42 AM
03/03/12 03:42 AM
MontyMcV  Offline
Trail Leader
Joined: Jun 2003
Posts: 7,340
Cleve-burg OH USA
edit: I have been looking on line for parts and a confused. Are there two cats up front on the Gen 2.5 a left and a right?

The CA emissioned ones have precats coming from each exhaust mani, connecting up as a part of the y-pipe.

Assuming you have the pre-cats, another options would be to gut them. There is spacer to move the O2 out from the pipe a little, or you can get an electric thing-a-ma-jig that manipulates the code to the ECU. I think they can be found on 3SI for ~$50 each. Haven't tried either, but plan to if I keep my 95 and rebuild its bottom half.

Big Truck: 00, 3.5, Endeavor, 5-Spd drive line in hand!
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Her Truck: 03, 3.8, 20th Anniv, 65k
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