96 FJZ80 header pipe to 94 exhaust manifolds

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Howardkats

Howardkats

10 Year
Joined
Dec 21, 2013
Threads
9
Messages
40
Location
West Point, UT
Hoping someone has experience with my issue. On my '94 my exhaust is a bucket. I am installing custom sliders and the superwide double phat CAT is in the way. Without concern for the Federal emissions laws I would like to install the '96 inline dual CATs with the '96 front header pipe welding in O2 sensor bungs on the header pipes after the manifolds to maintain my '94 ecm emissions system. I know I will need to lengthen my harnesses for the 2 front 02 sensors. To the point of my question: Will a '96 front header pipe bolt up to `94 manifolds? I know the manifolds are different because of the air injection but I am hoping the output size and angles and flange mounting are the same.
 
well first thing is to get rid of the PAIR system if you dont have emissions and move the O2s up there. then you dont need to weld on new bungs or any of that crap.
 
slow95z said:
well first thing is to get rid of the PAIR system if you dont have emissions and move the O2s up there. then you dont need to weld on new bungs or any of that crap.
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I do still need to pass emissions. Nobodys going to look underneath and know the difference. It just needs to pass a smog test.
 
ahh, well the way you said it made it sound like you could do anything you wanted. why not take it to a shop and tell them what you want? the local places where i live are very affordable.
 
slow95z said:
ahh, well the way you said it made it sound like you could do anything you wanted. why not take it to a shop and tell them what you want? the local places where i live are very affordable.
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I actually did, they wont mod or change anything pre-cat. I can order from Bosal or Eastern the frontheader with the front CAT as one piece, just trying to figure out before hand if it will fit '94 manifolds.
 
Go to a different shop! Go to a locally owned "good Ol boys" shop that will do what YOU want. You can use a single 3-way cat to pass smog. Cheaper and takes up less space under rig.
 
Well I made the plunge and purchased the '96 Front Pipe and it fits the '94 manifolds . . . after some tweaking. I believe the Fedex guy or the handling through Fedex bent the two pipes closer together. They shipped it naked. The two flanges were within a 1/4" of each other. I spread them back apart but I had to grind the weld off the flange and reset the position and re-weld it.
 
02 sensor question: To run '94 02 sensor style I would need to weld new bungs in the down pipe within 8" of the manifolds before it T's into one pipe and put extension harnesses on them which I really would rather not do. Since the '94 FJ's ran an 02 sensor in each front down pipe and the '96's ran 1 front sensor in the single pipe pre-CAT any problem running both sensors in the same pipe Pre-CAT or could I run just one sensor and put a simulator on the other harness?
 
Damn, wish I had seen this sooner, I could've maybe helped.
I did the same thing to my '94 with a Magnaflow cat/ y-pipe. It fit the exhaust manifolds perfectly and the I skipped the second cat and had an exhaust shop bend a pipe and fit a new no-name muffler (sounds really great, actually). I eliminated PAIR so I didn't have to deal with bungs, except for blocking off the single upstream bung on my new pipe. I made a block off plate out of 1/4 for that.
 
AaronM33 said:
Damn, wish I had seen this sooner, I could've maybe helped.
I did the same thing to my '94 with a Magnaflow cat/ y-pipe. It fit the exhaust manifolds perfectly and the I skipped the second cat and had an exhaust shop bend a pipe and fit a new no-name muffler (sounds really great, actually). I eliminated PAIR so I didn't have to deal with bungs, except for blocking off the single upstream bung on my new pipe. I made a block off plate out of 1/4 for that.
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So you are not running any 02's?
 
Howardkats, my O2 sensors are in the manifold bungs that originally were home to the PAIR tubes.
 
Howardkats said:
02 sensor question: To run '94 02 sensor style I would need to weld new bungs in the down pipe within 8" of the manifolds before it T's into one pipe and put extension harnesses on them which I really would rather not do. Since the '94 FJ's ran an 02 sensor in each front down pipe and the '96's ran 1 front sensor in the single pipe pre-CAT any problem running both sensors in the same pipe Pre-CAT or could I run just one sensor and put a simulator on the other harness?
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You're going to want live O2 sensors in each side of the Y, before the cats. The simulators that you can buy for cat elimination give a steady voltage which fools the computer into thinking there's a functional cat in place. The data that your truck is looking for in the upstream sensors (the ones you're talking about) is going to be a dynamic, variable voltage that depends on current conditions. Basically the 02 sensors upstream are used to actually run the truck and the O2 sensors found downstream of a cat (in an OBD2 application, none in our 94s) are used to verify cat functionality.

So to finally answer your question, if you wanna keep PAIR you'll need to weld in some bungs and block that existing one off.
 
I'm paying close attention. I also want to do this at some point. I have a 94 but the motor was swapped with something newer so I don't have the PAIR valve bungs in the manifolds. That sure would have made things easier.

Curious what you work out.
 
just remove the PAIR and relocate the O2 sensors. I bet it will pass fine with out the PAIR. It will also look close to stock. it will be so much better than fabing a spot for O2 sensors. They will bolt right in.

I would also like to know if the later down pipe fits the 94 manifolds. If i got ridof the 94 style cats my sliders would be that much simpler.
 
rc51kid said:
I would also like to know if the later down pipe fits the 94 manifolds. If i got ridof the 94 style cats my sliders would be that much simpler.
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Yes the newer down pipes do fit the 94 manifolds. I just replaced my stock down pipes with the MagnaFlow that has the 95+ part number. Made a blockoff plate for the 02 hole and moving my two 02s up into manifolds where the pair was.
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I never followed up with how my project finished out. I did end up ordering a full exhaust system using the Bosal brand. The '96 down pipes do fit '94 Manifolds. Mine were bent from shipping a touch but I bent them back and they cinched up tight and never did leak. I used a block off plate for the upstream sensor bung and the down stream sensor bung after the post CAT. I ordered 2 Toyota bungs and welded them equal length 8" from the Exhaust manifold. The Bosal system didn't line up well with the rear exhaust mount above the rear axle. I ended up getting a universal mount and bolted to an existing frame threaded hole. They system passed emissions flawlessly, readings were better than I have ever seen it with 194K miles. The truck runs smoother, seems to have a bit more power and no CAT rattles (mostly from less-restriction of old CATs). No check engine lights and the emissions tech never was the wiser for a visual inspection.

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