Help! What does your Cat look like?
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New User
Joined: Jan 2001
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From: TX
Help! What does your Cat look like?
I failed emissions testing with my customized '90 EFI Bronco. The Air pump is sending air into the exhaust AFTER the cat. Is this right? Diagrams and descriptions I've seen lead me to believe that it should be injecting fresh air INTO the cat. Is mine backwards?
Senior User
Joined: Jul 2003
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From: Nashville
Yes, the air should go in before the cat. Idea is to provide oxygen and make the catalytic reaction more effective. EFI 300's did come with a dual convertor setup on some years, and the air tube does connect between the small front "pre convertor" and the larger rear cat. In the factory EFI Y pipe, the front "pre convertor" serves as the 2 into 1 collector. So...if you have only one cat, and it has two inlets/ one outlet, then that's just the pre-converter. You'll need to either bolt in a second factory style convertor, or get a new Y pipe designed to replace the factory dual setup with a single cat. The Y pipe runs ~$50, and that would let you use an aftermarket high flow converter
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New User
Joined: Jan 2001
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From: TX
Excellent!, That's it then. It's a '90 4.9L with only the front "pre-cat". So it sounds like the thing I need to do is get a Y pipe and a high flow cat. Should it still pass emissions w/that set-up? And any comments on where to get the components?
Thanks a bunch
Thanks a bunch
Senior User
Joined: Jul 2003
Posts: 311
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From: Nashville
Most auto parts stores can order the y-pipe, it's Walker #45166, about $50. Walker also makes high flow cats sold under the Dynomax name. Jegs or Summit would probably have the best deal on one, but shop around and see. As far as whether or not it'll let you pass smog...dunno...but this will at least put the exhaust system back to a "legal" stock replacement setup.
Not sure if the Y pipe has an air pipe fitting, if not you'll need to either weld one in or get a cat with the air tube connector built in.
Not sure if the Y pipe has an air pipe fitting, if not you'll need to either weld one in or get a cat with the air tube connector built in.
Elder User
Joined: Jul 2004
Posts: 911
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From: Northern Virginia, USA
Doug84- What exactly failed on your emissions? My 88 4.9 failed today, blowing TONS of NO2. Hydrocarbon and CO were way low though. I'm going to pull codes tomorrow and play with the EGR.
Also, is the Walker Y pipe "better" than the factory pipe? Mandrel bends? No kinks?
Also, is the Walker Y pipe "better" than the factory pipe? Mandrel bends? No kinks?
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New User
Joined: Jan 2001
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From: TX
HC 2190 over the allowed 162 FAIL
CO 11.65, 2.01 allowed FAIL
NOx 830, 2198 allowed PASS
I'm gonna put a new universal cat on today and retest tommorrow or Mon. I'll let you know
CO 11.65, 2.01 allowed FAIL
NOx 830, 2198 allowed PASS
I'm gonna put a new universal cat on today and retest tommorrow or Mon. I'll let you know
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Elder User
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From: Northern Virginia, USA
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Post Fiend
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From: Northern California
My 1981 with the 4.9 had both, the small one plugged, sooo...
I just had the small one up front gutted, and had a new multifunction universal cat installed where the big one under the cab, before the muffler was. It passed with flying colors!
Another thing most people forget is to change their oil before a smog inspection. Dirty oil can make you fail, HCs as well.
I just had the small one up front gutted, and had a new multifunction universal cat installed where the big one under the cab, before the muffler was. It passed with flying colors!
Another thing most people forget is to change their oil before a smog inspection. Dirty oil can make you fail, HCs as well.
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