No experience with replacing the exhaust manifold on the 4.0. The typical failure is cracking. Supposedly the 4.0 exhaust manifold after about 2002 or so was one of the better, more reliable pieces. What has happened with yours?

If you think its cracked based on sound alone, I'd encourage your to check the bolts holding the cats to it. Mine have loosened several times over the years.

 

Thanks. It's making a flakey rattle that is mostly on startup. I'm also smelling exhaust. My manifold is original and never been touched. However...

History - a couple of years ago #2 and #3 injectors went beast mode from their wires touching each other while I was on a trail. I got off the trail and ran for home 120 miles away. I have always suspected that raw fuel was dumped into the exhaust manifold and pre-cat down stream. I imagine it superheated everything. Until lately, I haven't had an issue except for a P0420 code which pointed to the pre-cat and the rattle exhaust smell being from the exhaust manifold. That's a bummer because the exhaust after the manifold was newer leading up to the injector fiasco. We won't talk about the PCM the injector issue fried as well.

I'm thinking the worst case scenario is exhaust manifold replacement - rattle, smell. And maybe the pre-cats - P0420 code. I'm not sure if I can get the Magniflow pre-cat part without buying their whole exhaust.

 

If I had to replace my exhaust manifold I’d do a Banks header set up.
You can go to Irwindale and pick it up from the factory.

 

Thanks Bob. Appreciate that. I’ll check that out. I know the bolts are difficult enough with a stock replacement. Any experience with the Banks and installation?

 

Thanks Bob. Appreciate that. I’ll check that out. I know the bolts are difficult enough with a stock replacement. Any experience with the Banks and installation.

Sorry, not on a Jeep 4.0.

 

So, I upgraded to a AFE Header/Manafold. Its a good product, but before I go to a new manifold, a few things to check.

On the LJ I am working on I pulled the intake and exhaust manifolds. The bolts/studs that hold on the manifold were all but rusted away. The manifolds are held on by common nuts and cone washers. The washers can expand and contract as I understand. So after many years these washers loose their ability to do their job and the bolts/studs deteriorate as well. I know mine were not serviceable again after I pulled them off. They were all but rusted through.

My thinking is this may be your issue more than the actual manifold being cracked. It is at least worth checking before investing hundreds into a next stainless steel header. I would go ahead and pull a bolt or two and see if they seem to be doing the job. Might even order replacements all around and just do that first without taking anything off. This would be fairly straight forward except for the front and rear nuts.

As far as doing the whole job, it's a pain in the ass. You may as well do the cats while you are there, heck just a new exhaust, you will be taking most of it apart anyway. I would take the hood off, or at least prop it on the windshield, take the fender off and even remove at least the upper DS control arm for extra clearance. I did mine while converting to a 3 link front so this stuff was out of the way, so guessing here on a stock rig.

Oh, one more thing I ran into, the DS hit the new AFE setup on close to full bump. I have not figured that out yet, I also have a 60 up front now. Ill figure that out when I get back to the jeep project. Moved into a new house a few months ago and the jeeps have taken quite the back seat to everything else.

So, basically, make sure the fasteners holding on the manifolds are in great shape, then go from there.

 

Good advice on the bolts. I was going to ask about removing the fender to make things easier. I had it off when I did the AEV fender thing. I have an aftermarket exhaust that is jointed under the oil pan. I grabbed the engine side and man handled it. It did move. I also noticed that its natural position rested against the oil pan. That bothered me, but I saw no scuffing. You may be right about those washers.

 

The connection to the cats is set up to move a bit as well. You can tighten them down in different positions.

 

The good news is that the exhaust manifold looks in good shape (OE 2004) and firmly attached. All bolts were tight with only one moving 1/4 turn.

The bad news is that the forward precat donut shaped screen was detached and warped inside the precat void. The rear precat looked remarkably new. Even the damaged one looked new as I looked at the screen as I shook it in place to view it. This was five years after installation and a 120 mile run for home with #2 and #3 injectors spewing fuel. The sound I was hearing was the donut shaped screen bouncing around. The smell of exhaust and shift of the pipe against the oil pan was from a slightly loose connection at the precat exhaust manifold connection.

The exhaust manifold is a two piece design. Each piece feeds its own precat. When my #2 and #3 injectors grounded out they spewed fuel and hell into the forward exhaust manifold and into its dedicated precat.

Magniflow does not sell the precat section of the 458027 exhaust I own. They we’re going to offer some type of warranty until I dug up my receipt showing five years have passed. I have to buy the entire exhaust that I paid $900 for in 2016, but now is sold for $2800, but I did find it at one source for $2100. It’s got to be a Nazifornia thing.

I guess I should count my blessings that I had a year or two of good smog checks after my injector fiasco. And my PCM is indeed throwing a legit code as opposed to a faulty PCM code.

 

The good news is that the exhaust manifold looks in good shape (OE 2004) and firmly attached. All bolts were tight with only one moving 1/4 turn.

The bad news is that the forward precat donut shaped screen was detached and warped inside precat void. The rear precat looked remarkably new. Even the damaged one looked new as I looked at the screen as I shook it in place to view it. This was five years after installation and a 120 mile run for home with #2 and #3 injectors spewing fuel. The sound I was hearing was the donut shaped screen bouncing around. The smell of exhaust and shift of the pipe against the oil pan was from a slightly loose connection at the precat exhaust manifold connection.

The exhaust manifold is a two piece design. Each piece feeds its own precat. When my #2 and #3 injectors grounded out they spewed fuel and hell into the forward exhaust manifold and into its dedicated precat.

Magniflow does not sell the precat section of the 458027 exhaust I own. They we’re going to offer some type of warranty until I dug up my receipt showing five years have passed. I have to buy the entire exhaust that I paid $900 for in 2016, but now is sold for $2800, but I did find it at one source for $2100. It’s got to be a Nazifornia thing.

I guess I should count my blessings that I had a year or two of good smog checks after my injector fiasco. And my PCM is indeed throwing a legit code as opposed to a faulty PCM code.

You might try taking it to a muffler shop and Just have the mini cats replaced. Lexus uses the same cat so they are readily available. That’s what I did when mine failed, it was about $750.00 and CARB certified.
Arce Muffler in Whittier, not far from you.

 

Will do Bob. Thanks.

 

Definitely do check a muffler shop. I had both of mine replaced after a head rebuild a couple years ago and it was only $500-something installed for both. They did use Magnaflow, too, but maybe not the same part # as yours?

- DAA

 

Commiefornia is a whole different beast when it comes to exhaust (emissions) stuff. Replacements have to be CARB certified and they do check serial numbers during smog checks. I had to take mine to a “Star” certified station last time it needed a smog check, regular smog station wasn’t good enough.
You are fortunate to live in Utah.

 

I drove by a shop today that is going to remove, repair, install, and check for leaks for $630. He had an "I want to help attitude." My job is to put everything back together and drive it to his shop. He has to "dance" for California and verify the vehicle for CARB (California Air Resources Board) rules to make sure he puts on the right precat. I'm still pleased I pulled everything apart because I saw my exhaust manifold was good, I saw the actual problem myself, and you guys were able to bring me to the best solution.

Much appreciated. I'll do a short follow up after the repair.

 

Sounds like a bad cat to me. Pouring gas down and super heating - seems like you made a raspy glass pack out it. My Uncle would tell me the thing back in the days was to take a New glass pack and cat, fill them with water and stuff potatoes on both end to rust them out on the inside on purpose before installing them. Made them extra loud and noisy. Maybe the same effect you got by dumping raw fuel down the manifold? Didn’t read every post after the first few, maybe you got it figured out by now.

 

Yeah, the forward one downstream of the hell. The precat is ordered and will arrive in about a week.

 

Good update - it’s been a week since having the forward precat cut off and replaced by welding with a CA approved precat. All is good and warrantied…..unless I ground another set of injector wires 😁

 

Took this picture of the welied/replaced precat. It’s a whole other world with that front driveshaft removed.
Note to self - there’s that access I needed to reach that O2 electrical connector by the firewall.