Exhaust Manifold Replacement: Any How-To? What Else To Do While In There?

[phenryiv1]

I have a crack in my exhaust manifold on my Renix 4.0L '88.  I purchased a Pacesetter header to replace the cracked stock part but I could not find a how-to on any of the XJ sites or in the forums here that detailed the removal of the manifold and install/re-install of the header/manifold.

 

2 Questions:

 

1. Is there a how-to page/post/thread that I might have overlooked?

2. What else should I consider doing while I have the exhaust manifold out and am upgrading?  Obviously the gasket, but anything else?

 

Thanks!

[yxmj]

Might be more of a job than you think.

If the exhaust gasket is combined with the intake gasket. (and i believe it is.....intake has to come off)

There are 2 bolts on the bottom that you will need either 2 sets of hands to get (or one really small set)

[phenryiv1]

Fortunately the MJ is not a daily driver, so downtime is not too much of an issue (other than losing a parking spot in the garage for my daily driver) but I took one look at it and had no misgivings that this was an easy undertaking.

 

I don't have concerns with it being an in-depth job (I rebuilt the motor on one of my projects and did a full rebuild and motor/trans swap on another) but in both cases I had a good guide to walk me through.  I have the FSM for the MJ (somewhere) and the XJ Haynes and Chilton's manuals (hmmm, I just realized that I have those...maybe I should check there) but in my automotove life I am rare to find that books/manuals do a better job of explaining the task than do fellow enthusiasts.

[Keyav8r]

I replaced the exhaust manifold on my 88 MJ with a NOS manifold. The gasket is one piece for intake and exhaust, but that doesn't really matter much as the same bolts/studs hold both manifolds to the head. It is not what you would call real fun. You can do it alone but when you are bolting everything back up an extra set of hands will help a lot.

Park the truck and hit all the bolts and studs, the downpipe studs and nuts, the O2 sensor and the EGR tube (both ends) with PB Blaster and let it soak overnight. Then hit again the next day while you are taking the power steering pump bracket off the engine.

Get the O2 sensor and the EGR tube off before you unbolt the manifolds. Since you are replacing the manifold, and should replace the O2 sensor at the same time, it won't matter much if you round off the O2 sensor and/or twist off the downpipe studs butit will make it easier to get the manifold off if you can unbolt these things. It is important that you get the EGR tube off in one piece because don't AFAIK a new EGR tube is not available from parts stores. Could be wrong about that, but I don't think so.

My job was made easier as I replaced the downpipe when I replaced the manifold (actually, replaced the whole exhaust system). So I can't comment on whether you can get the old manifold off and the new one on without removing the downpipe.

Other than the above, all I can tell you is that it's a lot of wrenching, saying unkind things about automotive engineers and MJs in general, and the occasional busted knuckle.

I highly recommend a good pair of mechanic's gloves and taking your time. If you get frustrated, slide out from under the truck, get a cool drink, rest a few minutes and then go at it again. It's not the worst repair job I've ever done, but it's in the upper percentile.

BTW, while you've got the manifold and downpipe out of the way, it's a good time to replace the motor mounts if you haven't done that.

[phenryiv1]

THAT is what I needed (no offense to previous posters) - the recommendation to do the mounts at the same time.

 

I actually have a mod-rise lift (48" lift with my door open) in the garage so it may make life a little easier versus crawling under the trick.

 

My cat section and muffler are both fairly new so nothing downstream should be too tough to detach.

[Keyav8r]

Forgot to mention - use Never-Sieze on the O2 threads, the EGR tube nuts and threads, and the downpipe studs (might as well use it on the manifold studs/bolts also).

Getting the EGR tube back on took some time. There will be some variation in the exact location of the fittings on the old intake and the new exhaust so it may be hard to get it lined up correctly and the nuts started without cross threading. I didn' t think of this when I did mine, but if you leave the manifold bolts/studs a little loose it may be easier to get the EGR tube on. Use a small wire brush (Harbor Freight special) to clean the threads inside the nuts and on the manifold fittings then coat all of them with Never-sieze before you install the tube.

Do NOT try to bend it to fit. It is 30 years old and has gone through thousands of cold/hot/cold cycles and may be brittle.

[jimoshel]

If I can reach the crack I weld it. If I can't reach it, I forget about it. Hack! Cough!

[phenryiv1]

If I can reach the crack I weld it. If I can't reach it, I forget about it. Hack! Cough!

I was not worried about it either for the last 6-7 years that it had the crack but it failed the required annual safety inspection so I am stuck fixing it.

 

I had wanted an excuse to justify buying a PaceSetter but now that I have one I am still not thrilled to actually do the install.