Cat Removal

[cham]

Anybody have experience with removing those pre-cats?  My cats are starting to choke the engine out and I can tell the engine is struggling at highway speeds.  I've had P0430/420 codes intermittent for a while now. 
 
What techniques are there to make life easier?  I've been soaking as many bolts as I can get to with penetrant for a good while.  I'm curious if the 6 bolt heads on the upper face/side of the cat are accessed from underneath or engine bay side.  I saw a video of someone removing the entire exhaust manifold and cat as a unit for the driver side; but that looks next to impossible for the passenger side.  
 
I'm willing to remove the down pipe off the bottom of the pre-cat as well so I can lower the cat down and out.  The FSM diagram makes it look like the bolt heads would be accessed from underneath shown in the figure below.  Also it looks like for that upper six, some of the fasteners its a stud and separate nut where as some were just bolts. I'll probably have to remove those cat heat shields first before anything can be done.  
 
My question is, can all of this be done from underneath or will I have to remove the exhaust manifold and come from the top engine bay side?
 
 

Edited April 11 by cham

[hawairish]

I did everything from the bottom (3.5L). In fact, only way I could really even get up there was with the lower cats off (or resonators on some models).  
 

Getting the head shields off the uppers was the tough part…a few 10mm are in very tight spots. Some sheared off due to rust. Penetrant wouldn’t hurt.  Once the shields are off, you’ll still need/want socket extensions and wobbles to give yourself leverage below the chassis…working space is still tight. 

 

Access to the RH upper O2 sucks.  All others are easy (LH upper from the top).
 

I can’t remember if everything was nuts, but I want to say some were bolts. I know I sheared a couple on the drivers side and had to pull the exhaust manifold off to repair. Passenger side is a nightmare…fortunately didn’t have to remove that manifold and didn’t shear any. 
 

Also, I basically needed to remove the entire exhaust system to pull the uppers off. There wasn’t enough slack in the hangers to pry things backwards, so I removed everything starting from the rear. 

[cham]

Hey hawairish nice to talk with you again!

I was planning on removing that resonator/rear cat section with the downstream O2 sensor to give room for the pre cat egress. You’re saying that’s still not enough room?


Yeah I certainly am worried about shearing off those upper 6 pre-cat fasteners. If it happens on the passenger side I don’t see how there’s anyway to remove the exhaust manifold on that side haha.

Ive also wondered if maybe I should give that exhaust manifold a fresh new gasket. Are our exhaust manifolds and gasket (3.5L) ever known to crack or leak? I might do a smoke test once I remove that lower resonator section just to see if I have any manifold leaks and see if it’s worth it.

Curious what an exhaust shop would charge and if they’d do it right.

Did you replace the studs that connect the pre-cat to the manifold or just the nuts?


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[hawairish]

Even with the lower cat+pipes off, the proximity of the manifold/upper joint to the chassis still makes accessing all the nuts (6 per side) difficult. That’s where the extensions are needed, mainly for the ones at the top or towards the chassis. 
 

I replaced what I could with what I could on hand. I think in one case that meant replacing a bust stud with a bolt after extracting the stud and re-tapping the hole (holes…pretty sure I re-tapped everything).

 

Can’t confirm if leaks are common. Mine seemed ok, but I did replace the gasket on the drivers side. I absolutely avoided doing anything on the passenger side. The heat shield blocks everything, and just gaining visibility to things seemingly required pulling the steering pump and reservoir, among many other things. Right now with my SAS project still underway, I have those components out and it’s still largely out of sight. I expect the coolant pipe also obstructs things, so that’d have to be drained. I’ll try to get a pic of things tonight since I have things cleared out of the space. 

[cham]

31 minutes ago, hawairish said:

Even with the lower cat+pipes off, the proximity of the manifold/upper joint to the chassis still makes accessing all the nuts (6 per side) difficult. That’s where the extensions are needed, mainly for the ones at the top or towards the chassis. 

Noted, I want to take off that resonator/rear-cat section off anyways to see if the pre-cats have broken apart and maybe lodged pieces within the resonator.  But removing the entire exhaust would be nice so I can test for leaks off the vehicle.

 

I'll try working at the bolts when the exhaust is warm and giving the bolts heads a nice whack before unscrewing to maybe free them up.  Would you advise for or against an electric impact with extensions?  

 

Also I've got some pretty bad valve cover seepage onto my exhaust manifold/cat heat shields.  The VCs are the next job after this but I wanted to address the cat issue first.  If lets say I shear the heat shield bolts and can't get the shields back on during re-installation, will that increase my chances of a fire hazard since the oil will be dripping right onto the exhaust manifold?  So far I haven't had any smoke just burnt smell after driving.  

Edited April 11 by cham

[hawairish]

I’d advise against impacts unless you ended up needing to just shearing something on purpose. I prefer to feel those out, even stopping to reapply penetrant. 
 

For the heat shields, there are a few screws that hold them on, so even if you shear a couple you might be okay. Obviously oil on a heat source is not ideal, but worst case might be a large hose clamp securing the heat shield. 

[cham]

Yeah I saw some posts of people using an electric impact in its lowest setting and being careful with great success.  I might try it on inconsequential stuff first. 

 

You're right, worse case scenario I can just use hose clamps in the mean time while I order the valve cover parts.  Going to try to get them from oversees since they are a fraction of the cost for OEM, just might take a while.  

[cham]

@hawairish did you reuse the "washer" and "mesh washer"  in the exploded diagram screenshot in my original post?  Maybe replacing just that washer gasket would suffice and not the mesh?

[hawairish]

Mine didn't have the washer or mesh washer, and it didn't look like anything had been replaced previously...stock manifold and uppers as far as I could tell.  I looked for those items, too.  The upper had a lip that seemed to fit well into the manifold opening, and sealed fine when bolted together.  Looked on RA and couldn't find suitable replacements, and sure as hell wasn't paying $20/ea x 4 items to replace items that weren't there and didn't seem to present a problem.  

 

But, looking at RA now, I see a Fel-Pro mesh washer (p/n 61339) is on closeout for $3.33/ea that I don't recall seeing previously apparently because it only shows up in a search by OE p/n, and not by my application.  Fel-Pro 60835 reads like it might be the washer ("Converter; Manifold To Converter") but it has no matching OE p/n and zero specs...it looks too small and of one OE p/n it does list, it returns as a match for the gasket that goes between the upper cat and lower cat/resonator.

 

Looking at a pic of the washer, it's hard to tell if it crushes; looks like it has squared edges.  Frankly, I'm not even sure what the mesh accomplishes, but maybe I'll pick some up.

[cham]

That's interesting.  Do you think maybe the washers were crushed so much they were kind of stuck in the rim of the converter and/or manifold? Like as if they looked apart of the converter or manifold?
 
This is straight out of the 2002 FSM; you can see it specifies the exact alignment of the washer and mesh washer:
 
 

Edit:

 

Just found what you were talking about.  On RA looks like Fel-Pro 61339 is the "Mesh Washer" and 60835 is the "Washer".  I can tell based on the photos.  Also looks like the Fel-Pro "Mesh Washer" does reference the correct OEM P/n.  They look identical to the OEM parts found on NissanPartsDeal.  Can you attest to the quality of Fel-Pro for something like this?  Or should I probably leave the factory washer/gaskets alone and reuse them if they are there?  And I agree, no way I'm paying $90 just for these gaskets.

 

 

Edited April 13 by cham