Exhaust manifold replacement: what else should I do at the same time? Share some wisdom & save me some time

TRevs

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Fist thing I noticed when I test drove the YJ was a high pitched whistle with certain throttle positions. I figured it was a TB or vacuum leak, but a few weeks after I bought it I noted huge cracks in the exhaust manifold.

The parts are here so I’m starting now, and I’m just wondering if there are any other maintenance items that would be good to do at the same time since the left side of the engine bay will be completely disassembled and the fuel system is depressurized etc.

Suggestions welcome!

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machoheadgames

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I didn’t really do anything special when I did mine. There’s not much on that job that removing parts gives you access to. Maybe motor mounts if those are in bad shape. If so then I’d do new mopars.
 
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TRevs

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Great to know!

Is throttle body cleaner ok for the entire manifold and fuel injectors? Brake cleaner?

It’s ok to reuse the injector O-rings?
 

doc-ketamine

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Post pics as you’re going. This is next on my list and I’m a little nervous myself. I have an 89 4cyl with exhaust manifold leak 👍
How does one know if they have an exhaust manifold leak, or a leak somewhere else along the exhaust? I wonder if I have a leak but am not sure how to check. Passed emissions inspection though.
 

Flyer58

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How does one know if they have an exhaust manifold leak, or a leak somewhere else along the exhaust? I wonder if I have a leak but am not sure how to check. Passed emissions inspection though.
If it's between the engine and catalytic converter I've seen a little black soot in the area. After the CC it's usually cleaner but you can hear a leak once you get away from the engine. A good sealed exhaust system is usually quiet.

The inlet pipe into the muffler seems to be a weak spot. It looked like a previous owner tried to weld mine together without much luck or skill. It was loud.

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bushyeyed1

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I would suggest checking out the motor mounts. It will be at least easy to replace the drivers side without all the stuff in the way.
 
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I would suggest checking out the motor mounts. It will be at least easy to replace the drivers side without all the stuff in the way.
I did order new motor mounts since RockAuto recommended it, but when I got a good look at the existing ones the rubber looks good. I may just return the ones I purchased...
 
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How does one know if they have an exhaust manifold leak, or a leak somewhere else along the exhaust? I wonder if I have a leak but am not sure how to check. Passed emissions inspection though.
I've had a noticeable whistle at certain RPMs in certain throttle positions. It could be any number of things, but when I got a look at the exhaust manifold from underneath it looked like there were at least two visible cracks with what appeared to be JBWeld applied by a 3-year-old.

I'll post photos on my build thread of the old manifold after it was removed.
 
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How does one know if they have an exhaust manifold leak, or a leak somewhere else along the exhaust? I wonder if I have a leak but am not sure how to check. Passed emissions inspection though.
I can also smell exhaust when idling, for example at a red light. The entire exhaust system looks rusty. I can also hear air leaks around the muffler. The entire exhaust from manifold to tailpipe is being replaced.
 
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Post pics as you’re going. This is next on my list and I’m a little nervous myself. I have an 89 4cyl with exhaust manifold leak 👍
I can't say anything about the 4cyl, but the bolts weren't as hard to reach and break free as I'd been led to believe.

I'll post what I have on my build thread.

 

bushyeyed1

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The passenger side is a little thicker. If you’re looking to spend some money for a better upgrade there is brown dog industries. I couldn’t get myself to spend the extra $100 though. I Just got mine from autozone I believe it was a dorman. You will definitely be able to tell if your motor mounts are bad. The thing about any old vehicle or motor cycle is fighting the urge to replace stuff while you’re in there. Here is a phot of how bad my driver side was when I just recently changed it.
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05B7C61F-B7FC-4E0F-BA10-7A66B9292A75.jpeg
 
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I can't say anything about the 4cyl, but the bolts weren't as hard to reach and break free as I'd been led to believe.

I'll post what I have on my build thread.


@disaster06 , If you haven't already, download the FSM for your model year from the Resources section. Those things are worth the price of the Supporting Member fee, and then some (but don't tell @Chris ).
 

Flyer58

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I don't know if all 2.4L are the same but my 92 had this cheesy motor mount lift under the standard mount on the right side. All I can guess is some design engineer had the wrong measurement and added this to correct a problem. Anyhow, it's junk and often cracks, as mine did.

I has the channel and plate materials to replicate the Brown Dog base.

Cheap OEM part
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Fabricated lift.
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TimberTim

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How does one know if they have an exhaust manifold leak, or a leak somewhere else along the exhaust? I wonder if I have a leak but am not sure how to check. Passed emissions inspection though.
exhaust leaks between the combustion cylinder and the O2 sensor will not pass a smog check . The 02 Sensor sees the fresh Oxygen entering through the cracks by way of the Venturi Effect and adds more fuel to the mixture to compensate for the misinformation. the results are a rich fuel mixture which can be smelled when the engine is running. Doc, I'll post my Smog Check readouts when I have more time.....Tim
 
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TimberTim

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Fist thing I noticed when I test drove the YJ was a high pitched whistle with certain throttle positions. I figured it was a TB or vacuum leak, but a few weeks after I bought it I noted huge cracks in the exhaust manifold.

The parts are here so I’m starting now, and I’m just wondering if there are any other maintenance items that would be good to do at the same time since the left side of the engine bay will be completely disassembled and the fuel system is depressurized etc.

Suggestions welcome!

View attachment 120688
straight edge the mating surface of both your exhaust and intake manifold. I found both of mine to be out of tolerance and used my 48" floor mounted Belt sander to dress the mating surfaces. cranking down the bolts to seal a crooked exhaust manifold is a prim reason for a cracked exhaust manifold ! Not to worry if you've already installed your manifolds, you can address this concern when you remove you manifolds to replace your Expansion Plugs ( Freeze Plugs) That you should have done when you had the manifolds off in the first place !!!!!
 
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TRevs

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straight edge the mating surface of both your exhaust and intake manifold. I found both of mine to be out of tolerance and used my 48" floor mounted Belt sander to dress the mating surfaces. cranking down the bolts to seal a crooked exhaust manifold is a prim reason for a cracked exhaust manifold ! Not to worry if you've already installed your manifolds, you can address this concern when you remove you manifolds to replace your Expansion Plugs ( Freeze Plugs) That you should have done when you had the manifolds off in the first place !!!!!
I’ve never looked into changing expansion plugs. Is that a difficult job? They are the 5 discs on the left side of the block?
 

TimberTim

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I did order new motor mounts since RockAuto recommended it, but when I got a good look at the existing ones the rubber looks good. I may just return the ones I purchased...

I’ve never looked into changing expansion plugs. Is that a difficult job? They are the 5 discs on the left side of the block?
No it's not hard at all .yes the discs, on my "91" the large ones were 2'' AND THE SMALL ONES under the Exhaust Manifold Gasket on the Head were 3/4" . Drain coolant and simply drive a flat screw driver thru the Brass freeze Plug and pry out old plug. Clean the block opening with a wire wheel and sand paper until shinny . Put a light film of RTV Sealant on the edge of the freeze plug ( this will seal any imperfection and act as a lube for installing). Gently tap the plug with a hammer until starts and it stays in the hole by its self. then place a piece of flat stock over the plug that covers all edges of the plug, our use a large socket ( upside down) that covers the whole plug and gently tap, tap, tap, the plug into the whole, Don't Bam, Bam, Bam, the plug. set plug depth to just a hair below the chamfer on the block. this should cost around $20 Bucks....Tim