Broken Exhaust Manifold Jeep 4.0

Broken Exhaust Manifold Jeep 4.0

I have been hearing an exhaust leak in my off road Jeep Cherokee for a couple of years. Knowing that the 4.0 manifold is likely to crack, I did not think much about it. However, the noise has been getting worse and I am starting to see some indication that the leak was causing some cooling problems under the hood.

So, I decided to take a look to see how bad the crack was. I began by using a mirror and a flashlight. I pulled the air box to get more room. I was able to look over the front four runners pretty well and found no visible cracks. I know that the later HO manifolds tend to crack where the two section join. But this is the older style manifold that has one main tube and the runners are welded to it. No matter how I twisted the mirror, I could not see the back two runners.

So I decided to pull the intake and take a look. In some ways the old Renix manifold is easier to remove and in some ways it is not. One of the things that makes it easier is that the whole injector wiring harness can simply be unbolted at the firewall and stay with the manifold. There is no need to disconnect the individual injectors.

I did have to disconnect the three sensors below the engine. The O2 sensor, the block temperature sensor and the knock sensor all had to be disconnected to let the wiring harness stay with the manifold.

I had to remove the power steering pump from the bracket to access the bolt that holds the bracket to the manifold. Then I removed the fuel and vacuum lines. I was not able to get the EGR line to break loose so I had to remove the intake and exhaust manifolds as a unit.

Once I had them out and on the shop floor, I was able to get the EGR line to break free from the intake. I immediately saw severe cracking on the last runner near the O2 sensor bung.

I flipped the manifold over and saw cracking around the number five runner as well. I pulled on the pipe sand the last two runners separated completely from the manifold.

I had planned to re-weld the cracks but after seeing how broken up the pipes were and how brittle the surrounding metal was, I decided to order a replacement. I looked into getting a header but there are few to choose from for the older engine. I also thought about retrofitting the HO manifold but that would have meant redoing the down pipe back to the catalytic converter. I decided to simply replace it with a stock type manifold from Crown.