The exhaust manifold on my 91 4.0L YJ was badly cracked, making a nice loud popping sound and generally making it sound like I'm running a diesel. I'm a fairly amateur mechanic so I was fairly nervous going into this repair. If I can do it, any of you can do it.
My equipment list:
- Good selection of sockets & wrenches
- Flathead screwdriver
- Needlenose pliers
- Brake cleaner / wd-40 & shop towels
- rubber mallet
- pack of cigarettes
9.5 hours. Yes, really. I had a good 2.5 hours of screwing around, and had I a better idea in my head of what to do, it would have taken less time. If I had to do this again, I'm relatively confident I could do it in 4 hours.
I ordered my manifold from 1AAuto for $130 USD. It arrived in a couple of days. It was packed very nicely, and looked pretty good. It came with the gasket, donut gasket, and flange bolts/nuts. I gave it a light sanding and acetone bath, then gave it 3 coast of rustoleum high heat black paint. Follow the directions on the paint, this stuff said to leave the item for 24 hours before applying heat to it. If you do this outside, there will be a couple ants and flies that likely go and get stuck to it. Don't worry, they'll burn off quickly enough.
-Disconnect negative battery cable
-Remove the airbox hose - mine had 2 plastic clamps that were easy to release, then remove the airbox. There were three snaps on mine that came off with ease.
-remove all of the vacuum and electrical connections from your intake manifold, and be sure to label them. I used painter's tape and marked them numerically. This made re-assembly easy as pie.
-Pry the accelerator cable from the pivot ball, then unbolt the accelerator cable's bracket from the intake and swing to other side of the jeep.
-Remove the vacuum line from the brake booster. I found it easier to remove the plug itself from the booster rather than the hose from the plug. It will take some effort, and you'll be rewarded with a nice "whoooooshhh" as you pop it out and the vacuum escapes.
-Label and identify all your injector wiring harnesses after you've removed them. You'll need to get the little metal clip pried away from the orange tabs to do this. A small flathead screwdriver and a set of needlenose pliers will be your best friend here. Make sure to pop the clip back into place once you've removed the harness.
-Remove the four bolts from the fuel rail, and give it a good tug to get the injectors out along with the rail. I had a hell of a time, and was certain I was doomed to failure at this point. I gave it a few more tugs and I was not gentle, and out it came - but it left 3 of my injectors in the block and fuel puking up all over the place (yes, I did de-pressurize my fuel rail first). Not
the end of the world, but they had to be pulled out of the block, the O-rings removed from the fuel rail, installed back on the injector, and the injector crammed back in - which wasn't exactly easy either. The O-rings are very large so it took some poking and prodding with a small screwdriver to get them in. Had I foreseen this issue, I would have bought new o-rings and perhaps even new injectors just for the hell of it. You can set the injectors and rail along the spreader bar, it should seat nicely and not move anywhere.
-Loosen tension on the serpentine belt and remove power steering pump. My hayne's manual says NOTHING about this topic, so I had to figure it out for myself. I didn't get any pictures of this due to my photographer being uninterested in coming outside at this point. There are TWO bolts on the back of the power steering pump, one nut you need to loosen on the front below the pulley, and a supremely long bolt on the driver's side of the pulley that you need to loosen / remove in order to release the tension and remove
the belt, then get the power steering pump & pulley out of the way enough to remove the TWO bolts holding it to the intake manifold.
-Remove the bracket that holds the hard fuel lines. It has two bolts and is near the driver's side fender, bolted to the intake manifold.
-After that's done, you can go ahead and fight with all the manifold bolts. Take off the bottom ones first, but do not unbolt the exhaust manifold from the collector just yet. Get your top bolts off, then manhandle the intake manifold out of the way (watch your injector wiring harnesses), and set it down somewhere you can clean it.
-Unbolt the collector and remove the exhaust manifold. Take a look at how badly yours is cracked, you'd be amazed the kind of damage that can be done if these are left alone.
-Clean the mating surface on the block VERY Well, you'll be able to see on the block where the old gasket was left. I used brake cleaner and a scrubber at first to get the light stuff off, then WD-40 and a sharp exacto blade to scrape off all the miniscule stuff, as well as all the places where the old gasket was fused to the block. That took me a good while - don't write off cleaning the surface, this is a crucial step.
-Clean the intake manifold. You'll likely be better off without an exacto knife for this part. Plenty of brake clean and a scrubber / shop towels should do fine. Some q-tips as well. Make sure to clean out the injector ports and scrape out as much gunk as you can, then get the mating surface nice and shiny.