Exhaust Manifold Gasket
You have no idea why your car is running poorly. All you know is that the check engine light is on. There's also been a bit of a rumble from the car. It looks like there's a leak somewhere, probably in the exhaust system. If something tells you that this could be the case, then you should have this checked right away.
Gases from the engine shouldn't infiltrate the cabin or other parts of the combustion system. They should go straight to the exhaust manifold that's connected to a series of pipes. These pipes will lead collected fumes out into the tailpipe of the vehicle. The manifold is sealed with an exhaust manifold gasket, and this gasket may blow out or break at some point.
Signs of a leaking manifold:
Failed emissions test
Failing to pass the emissions test usually points to a faulty exhaust system. Higher emissions may be caused by an imbalance in the mixture of fuel. It's possible that oxygen may be getting through the exhaust stream because of an exhaust manifold leak.
Strong gas odor
If the exhaust manifold gasket is damaged and gas is leaking, you may notice a strong gas smell in the emissions. You'll also notice high concentration of soot. This happens when some exhaust fumes escape the manifold, which is connected to pipes that go all the way to the vehicle's rear.
Strange engine noise
Strange noises from the engine shouldn't be ignored, as these can be a sign of a leaking exhaust manifold. You may hear knocking sounds, though this is a bit hard to distinguish from other noises made by a running vehicle.
How to install a new exhaust manifold gasket
Step 1: Look for the exhaust manifold under the hood (use a vehicle manual as a guide if you're not familiar with the part). Remove anything that blocks access to the manifold.
Step 2: Pull out the exhaust pipes that are connected to the manifold by unscrewing the bolts or fasteners that connect them. The manifold should then be disconnected from the engine block by removing the studs or bolts securing it.
Step 3: Detach the exhaust manifold after you've disconnected the pipes and other attachments. Set them aside some place safe, making sure that you won't be losing any hardware.
Step 4: Remove the old exhaust manifold gasket. Don't leave any piece of the gasket that's attached to the engine block. Scrape this off.
Step 5: Clean the area where the new gasket will be installed. Make sure that there won't be grime and grease stuck to the surface.
Step 6: Put in the new exhaust manifold gasket. This should go in between the engine block and the exhaust manifold, making sure that it's on the right spot.
Step 7: Reinstall the detached exhaust manifold using the studs/bolts to attach it to the engine block. The bolts should be torqued according to the specs from the manufacturer.
Step 8: Reconnect the pipes, braces, and other attachments. Secure them with tightened bolts and other fasteners.