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Replacing a Cracked Exhaust Manifold on a Jeep TJ Wrangler 4.0L Engine

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My 1998 TJ exhaust has been getting louder and started to backfire a bit.  It got really loud the last several days and when I crawled underneath the Jeep to take a look I found a pretty sizeable crack in the header.  

 

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How do people choose a replacement header?  There seems to be the ~$170 models,  ~$400 models which include the Mopar replacement model, and $500+ models with coatings and etc.  Is it a case of "you get what you pay for?"  How about the gasket between the manifolds and the head - is it important to use a brand name here?  

 

And when it comes to replacement, I was thinking I would try it myself.  I've had the fuel rail off when I replaced the cylinder #1 injector, and I've replaced the power steering pump before, so those parts of the job are familiar.  What will be new is breaking loose the intake and exhaust manifold nuts and bolts.  

 

With that in mind, a few questions...  

Should I plan to replace the threaded studs with bolts?  They are original and the Jeep a 1998 that has 258,000 miles.  Is it a big worry if one of these breaks - or is it straighforward to turn the stud out with a vice grip and replace it with a new one?  

How tightly do you torque the nuts when you put the header and intake back on?  

Any tips for cleaning the old gasket off the head?  

Is there a seal ring that goes between the header and the exhaust pipe?  

 

Just trying to figure out which one to purchase and size up the job.  I just have basic hand tools, novice skills, and my Jeep is my daily driver.  

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I went with a Borla header on the '99 Jeep XJ Cherokee. Banks also has specially "tuned" headers that many like. Fit is important. Route wires carefully to the O2 sensor and crankshaft position sensor.

Many, including the factory shop manual, suggest the complete removal and installation of the exhaust and intake manifolds as a pair. I found it easier to loosen the intake and exhaust manifolds, then stretch and tie the intake away from the cylinder head, using plastic rope.  The serpentine drive belt needs removal for the power steering pump clearance.  (The pump and bracket can be loosened from the intake manifold if necessary.)  The intake tube to the throttle body will likely need loosening.  I carefully watched the throttle linkage, hoses, fittings and all other attachments as I moved the intake manifold away from the head.  By not completely removing the intake, I saved considerable time and labor.  I moved the intake just enough to provide room for gasket removal and installation of the Borla header from the bottom side.  This worked for me on the Borla header installation.

 

Answers to Your Questions:

 

1) This installation involves both intake/exhaust manifold bolts and nuts/studs.  The threaded studs may or may not need replacement.  I would use a suitable thread penetrant spray on the nuts before removal to offset risk of snapping a stud.  These are tough, graded steel studs, and unless excessively corroded, you should be able to reuse the studs and even the nuts.  Use good judgment here.  Removing studs could be difficult with the intake manifold tied away from the head, you might find yourself completely removing the intake system.  Vice Grips work, though my preference is to double nut the stud and turn the inner nut outward to remove the stud.  If the threads are broken off the stud, Vice Grips can grab the remaining shank of the stud.  A stud that breaks within the head surface is a very difficult proposition to drill and "easy out".  The steel in the stud is very hard, and you must stay on center to avoid damaging the head threads and casting.

 

2) Torque nuts and bolts to factory specification.  The below PDF is the entire rundown on intake and exhaust manifold removal/replacement (the combined removal by factory method) plus the torque specifications.  Nuts have differing torque in various positions.  Note the illustration with the stud numbering sequence.  Read over the factory method in case you need to remove the entire intake manifold.  On the Borla header installation, I avoided this laundry list of steps by moving the intake manifold outward and securing with plastic rope, gaining just enough room to replace the intake/exhaust manifold's one-piece gasket and to slide the new exhaust manifold up into position over the studs:

 

1998 Jeep TJ Wrangler Manifolds.pdf

 

3) Modern manifold gaskets do not require great effort to remove from the casting.  A putty knife should remove any loose or remaining gasket, do not scratch the intake manifold aluminum

 

4) Depending upon the header kit, you may not have a gasket ring at the end of the header.  Borla uses a pipe-to-pipe, slip-on stepped pipe size arrangement and furnishes a connector pipe.  Clamps were exceptional quality and grade.  Banks has its approach.  See if you can find kit installation details and parts illustrations at their websites.  A stock replacement header would be Mopar OEM replacement parts much like your current setup.

 

This is not a monumental job.  The biggest concerns are the bolts, nuts and studs plus getting old exhaust pieces apart without damaging any parts that need to be reused.  Other forum members may have additional information and experiences to share.  The original header is a failure prone piece, and cracking is quite common.  Yours lasted longer than many do.

 

Moses

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Moses, thanks for the tips.  I spent some time this evening putting liquid wrench on the fasteners.  The ones underneath the manifolds are pretty tricky to reach!  

The Borla looks like it requires cutting the pre-CAT pipe - is this readily done with a hacksaw or sawzall?  The installation instructions make no mention of it.  I wonder if it's easy to get it cut to the correct length?  

I also saw JBA and and Banks headers that were direct bolt-ons, but the warranties among these three were quite different.  Borla = 1 Million miles, JBA = 1 year, Banks = 5 years.  

 

The crack is now a nearly separated pipe.  When it goes, it goes quick!  Other than noise and fumes, what risks are there with driving it this way?  

 

Also I noticed that the upper lip of oil pan had caught some drips of coolant.  Is it terribly concerning to have some coolant weeping on the manifold side of the block?  Is this a head gasket that's beginning to fail?  Is this a sign that it's time to overhaul/replace this engine or part with the Jeep?  The overflow bottle has coolant in it.  

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Glad to share my experience, jj_jeep...I like the Borla, it has a very substantial flange, no frills.  Not partial here if you can find a suitable alternative.  JBA and Banks could be good prospects with the fit you describe.  Use your judgment here, and let us know what you wind up doing, including installation details, maybe a few photos to help others in our forum community.  This is a common issue.

 

If your system requires a pipe cut, it can be done with a hacksaw and patience.  Sawzall would be choppy, and you need a smooth cut.  There's actually a tool for this: a chain cutter for muffler work. This one seems decent quality and price: http://www.amazon.com/GearWrench-2031DD-Exhaust-Tailpipe-Cutter/dp/B000M93OUM.  There's also a cutoff wheel, air driven.  I have a good one that's been very helpful over the years.  Here's an example at Summit Racing:  http://www.summitracing.com/parts/kti-88255.  The Jeep TJ exhaust system pipe to the cat could be stainless steel, and if so, it's quite hard and best done with a sharp cutter or an abrasive wheel.

 

As for the crack, I'm a TIG welder.  If finances were tight and the crack area were accessible and readily cleanable, I would stainless steel TIG repair the piece.  What the heck, right?  A quality TIG weld would exceed the factory weaknesses and buy time.  If there's much corrosion and the need to remove the piece for the repair, that might be different.  I have a great deal of confidence in TIG fixes if done correctly. Judging by your useful photo of the crack, this could not be welded/repaired in position.  The manifold would be removed for the cleaning and weld.  Position is critical, the piece must have the same shape after the weld/repair.  You might discuss this crack with a muffler shop that does custom installation welding, including stainless pipe and MIG process.  They may have an in-position repair solution for your header crack, though the response will more likely be similar to my comments.

 

Metallurgically, heat cycled stainless steel is either intact or cracked.  There's little risk of another crack forming at this location if TIG'd correctly with stainless filler.  (The factory assembly method is likely wire feed MIG stainless.)  Perforation with stainless is unlikely, fatigue is the common failure.  Following the repair, another fatigue crack might occur away from the weld later, possibly the heat affected zone (HAZ), though not necessarily if the piece cools properly during the repair process.  Stainless is hard and not ductile enough to tolerate continual expansion and contraction cycling.  On the other hand, it has substantial resistance to high heat over time and will not expand much in this application.  Stainless is definitely a good alternative to other types of tubular steel.  For emissions engines with catalytic converter systems, stainless steel works well.  A cast iron manifold would glow red from emissions A/F ratios and lean burn temperatures.

 

In driving the vehicle with this damage, beyond the obvious carbon monoxide poisoning risk, one concern would be valve warpage.  This occurs if the leak is close to the cylinder head.  When shutting down the engine, ambient or cold air can "scavenge" into the exhaust port under particular conditions and warp an exhaust valve(s).  This is highly unlikely if your crack is any distance from the head, which it appears to be in your case.  The crack is perpendicular to the flow, and scavenging this far from the head would be unlikely. 

 

The coolant weep could be blowing back from hoses, radiator or the water pump. More likely, it could be a freeze plug seeping, certainly not uncommon at this mileage.  Find the source, it's not the oil pan region itself and must be migrating from elsewhere.  If it is a freeze plug, this would be readily accessible with the exhaust manifold removed.  Changing a freeze plug is not difficult when done correctly.  We can discuss that repair.

 

Moses

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Bought a Dorman.  It was ~$215 so toward the lower end for cost and my local auto parts store got it for me in a day.  With the mileage and age of this vehicle I was OK with sacrificing performance and quality for lower cost.  Also, as you troll the net about the manifold cracks, it's not clear that any of them eliminate the root cause of cracks.  Whether myth or reality, people claim cracks on the Banks and Borla and Dorman.  People also claim the aftermarket are the best ever.  No clear answer so I picked convenience and price.  

 

Moses, with your method of easing the intake away from the head just enough to do the job...  did you still have to pull the fuel rail and injectors?  

 

Off to the garage...  

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jj_jeep...I did not remove the EFI components.  Just use good judgment and do not stress parts.  For your application, watch the cables, wires and hoses.  Go slowly to avoid stressing parts, disconnect any susceptible part and identify it with masking tape and a Sharpie if necessary.  Move the manifold(s) just far enough for removal.  If for any reason you do remove the fuel pressure hose, use the proper release tool at the spring connector.  Lisle and others make inexpensive spring release tool kits for A/C, fuel and other pressure/spring connections.  Do not force this hose connection apart, you will create the need for a very costly repair.

 

Glad you found a cost-effective solution.  I've had no trouble with the Borla, it's quite hefty and well-flanged.  The issue overall is metallurgy and stress.  Heat cycling stainless steel is a dicey proposition over time.  Any tubular manifold would eventually fatigue and crack.  I like the Borla for its thicker tube walls and smoother bends.  I noticed on your OEM manifold, as with my XJ Cherokee, the tighter end bends look susceptible to cracking.  And they do!

 

Please share your installation details and how well the Dorman replacement manifold fits...

 

Moses

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Half way.  Old is out.  Everything is cleaned up ready for new.  Thanks for the tip, Moses.  I did not disconnect the fuel rail or fuel injectors of the fuel line - grateful for that.  I wasn't looking forward to lining up 6 injectors back in the intake and fuel rail and stuffing that back together.  

 

The old header was broken on both pipes - The second one was hidden by the first one so I didn't see it until it was out.  I think the hidden one has been cracked for a while because I've looked for cracks before but couldn't find them.  

 

Anything else to do before reassembling?  

 

Header carnage

 

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Zip tied intake manifold with fuel system still attached

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Cylinder #1 - interesting to see it after all the cylinder misfire MIL's.  

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No obvious head gasket concerns or coolant leaks that I see.  Possibly leaking at block heater, but hard to say.  Liquid wrench ran down side of block when I was spraying manifold bolts.  

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post-27-0-04045300-1412465826_thumb.jpg

 

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I am pleased that moving the intake manifold out of the way and plastic tying it to the core support rod did the trick, jj_jeep!  This is such a time and labor saver.  The complete removal of the intake manifold and keeping track of all the components can be a major chore.  The old exhaust manifold is suitable for framing or hanging on the garage wall...Just kidding, it's truly ready for scrapping!

 

From the great photos, your freeze plugs look shot.  You need to replace these plugs while they're easily accessible.  By now, you've discovered the coolant leak, right?  For those unaware (Florida and Southern California Jeep owners), the last freeze plug looking device with the electrical connector is the block heater.  Is that your leak source?  It looks so, but this is the more costly piece to install.  If the heater unit has a cinch/expander bolt, try carefully tightening the expander.  This may reseal the plug.  If you're not confident of the seal, and if you use the block heater, price a new heater unit.   (Here's the best deal I could find for a genuine Mopar assembly: http://www.amazon.com/Cherokee-Engine-Heater-Mopar-82201506/dp/B007NPL3OM.  There are aftermarket units available for much less.  I'm use an aftermarket Kat block heater on the Cherokee, no trouble to date, though the Mopar unit is more rugged.)  Each of the other freeze plugs is a typical cup type.  Since you are likely going to replace any suspect plugs, I'll share my technique: 

 

1) Take a blunt or rounded punch and tap just inboard of the cup lip (on the dished area).  Do not punch a hole through the cup, you want to rotate the cup in the block bore and avoid driving the cup into the cooling passage if possible.

 

2) Whether the plug drives into the passage or rotates as desired, I grab the cup edge with a channel lock pliers.  Prying carefully, avoid scratching or marring the cup bore in the block, rock the channel lock's head to apply leverage.  (Pry against the block and not the bore.)  Cup perpendicular to the block now, pull the cup outward through the plug bore.  Do not leave broken cup pieces in the block, they will obstruct coolant flow.

 

3) Take crocus or emery paper (preferred for a corroded surface) and clean up the plug bores.  Avoid gouging or making deep scratches.  The new plug must seal completely in the bore.

 

4) I coat the outside edge of the new steel cup (not brass at this mileage, steel is stiffer and holds shape better than brass) with traditional Permatex Super 300 Form-a-Gasket sealant or equivalent.  I do not use RTV sealant here.  Coat evenly and apply a thin additional film around the block freeze plug bore.  You don't want excess amounts, as this will wind up in the block and can migrate and clog the radiator tubes.

 

5) There are freeze plug driver tools, usually with a swivel head.  I've done just as well by starting with a plastic sand filled head hammer, tapping side to side until the cup is clearly going straight into the bore.  Often, a heftier hammer and block of wood can drive the freeze plug into the bore evenly.  If not that easy, try an impact socket with an O.D. that fits just inside the cup edge.  Drive straight and avoid distorting or badly nicking the cup dish.  Avoid distorting or denting the cup's raised edge.  If unclear how deep to set the plug, note the OE installation.  I seat the cup edge even with or slightly deeper than the inner edge of the chamfer at the block bore.

 

This is a much easier task now than with the manifolds in place!  Regardless of the life left in this high mileage engine, you need dependability.  These freeze plugs are on their way out and could spring a substantial leak at an inopportune time or place. 

 

Share some pics with us.  It will be interesting to see how close to failing these freeze plugs turn out to be.

 

Moses

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Looks like freeze plugs (called expansion plugs on Napa website) come in deep cup and shallow cup.  Can either be used?  Any reason to pick one over the other.  2" diameter is what website says for 1998 Jeep Wrangler and that's matches my best estimate with a tape measure.  

 

Would you expect the block heater to come out like a freeze plug?  Reason I ask is it looks like it has a flange on it that might prevent it from rotating in the bore?  

 

Going to attempt this.  Might have to borrow a car - not sure I can get this all done before work in the morning!  But don't want to tear this all apart again if I can avoid it.  And don't won't to be stranded later by a blown freeze plug.  

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jj_jeep...Should be deep cup and readily available.  Remove your old ones first and compare depth of edge with new plugs.  Both types should be at the local NAPA store if reasonably stocked.

 

The block heater has an expander that loosens with the bolt in the element's center.  Loosen the bolt (not completely, or you may be digging parts out of the block passageway!).   The replacement unit uses an O-ring, and if the OEM has the O-ring, you may be able to "repair" your existing heater if the element still works.  The leak could be a loose or deteriorating O-ring.  I'd take the unit out if it's leaking and go from there.  You may be able to simply replace the O-ring with a reasonably heat resistant and anti-freeze suitable O-ring.  I looked in the Mopar parts catalog, they do not show a replacement O-ring.  You'll have to play this one out and see what's in there.

 

Do not attempt to "rotate" the block heater as you would a freeze plug.  It will come out and go back into the bore straight, just as you suspect.  It can be indexed if necessary but not pivoted.  Do not hit the heater element with a punch or hammer!

 

Moses

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Finished Sunday evening.  Went surprisingly well.  No broken bolts, bloody knuckles, or left over parts!  I've never replaced freeze plugs or an exhaust header before.  Aside from the number of steps, it was fairly straightforward.  I took a few pictures along the way that I'll post when I have more time.  It's amazing how poorly the Jeep ran when the header had only a small crack (which quickly became a big crack and then completely broke).  With the new header, the engine is smooth and quiet.  It feels like a turbo was added.  

 

I had to buy a bigger hammer and then the freeze plugs were easy.  A couple blows on a short socket extension held against the plug and they popped right out.  

 

It was very clear how the block heater went in once I had the new one in my hands.  It's more like a bath tub drain plug because it has an O-ring that seals it.  And then there's a piece on the back that's like a drywall anchor that folds out once it's in the wall cavity.  This is what the bolt pulls against when you tighten it up.  This is also a convenient place to drain the remaining coolant from the block.  

 

This job definitely built off of other work I had done before (replace serpentine belt, power steering pump, injector, flush and fill coolant).  It would have been more intimidating had I not done these building block pieces on previous occasions over the years.  I used every length of socket extension I own to get the manifold bolts in.  

 

Appreciate the advice Moses - it's also a confidence boost to know that knowledgeable help and advice is available on your forum.  More to come...  

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jj_jeep...You know, that cracked manifold would make the engine run poorly.  The dilution of exhaust and poor back pressure distorts the oxygen sensor readings.  It likely did smooth out, and your "knocking" or ping should be gone if that's the case.  Fuel efficiency might even pick up.  The cracks were not minor and affected some cylinders and not others.

 

Very pleased that the job turned out well.  The photos will be helpful to others.  You're building on your automotive/Jeep skills and becoming quite proficient here!  Who knows, that high mileage 4.0L may still have some life left.  You certainly gave it a boost!

 

Moses

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