An exhaust manifold is a stainless steel or cast iron assembly that gathers exhaust gases from different cylinders into one pipe, so they can exit the vehicle through the exhaust system. It features several passages, each of which corresponds to a specific cylinder, routing exhaust gases from that cylinder to the single base on the end where the manifold connects to the rest of the exhaust system.
Depending on the design of your engine, it can have either one or two exhaust manifolds. Inline engines usually come with a single exhaust manifold, while their v-type and opposite-type counterparts are equipped with two manifolds, one for each side of an engine. Regardless of the quantity, your exhaust manifold or manifolds are high-durable exhaust system parts designed to last the life of the engine. However, it can fail over time due to some engine problems, manufacturing defects or a road collision. The most common exhaust manifold failures are cracks and wraps. Both can cause an array of problems, including the following ones:
Exhaust gas leaks and abnormal noises
A cracked manifold will allow exhaust gases to escape from the exhaust system into the outside air. This can be accompanied by a tapping or rattling noise, which should be more noticeable when the manifold warms up as this causes the crack to expand.
Your check engine light turns on
Your engine control unit relies on the oxygen sensor to analyze the quality of the air/fuel mixture. A leaking manifold can cause the engine control unit to think the engine is running too lean, resulting in an illuminated check engine light.
A leaking exhaust manifold will cause the oxygen sensor to provide the control unit with incorrect data. As a result, the computer can command to add too much or too little fuel into an air/fuel mixture.
Poor fuel economy and high emissions
A faulty exhaust manifold will affect the operation of the oxygen sensor. In some cases, this can cause excessive fuel consumption, and, therefore, bad fuel economy and emissions.
Exhaust smoke and/or smell
Escaping exhaust gases have a noticeable odor you should smell when running the vehicle. If the leak is huge, you may see exhaust smog coming from under the hood.
While all these symptoms can be caused by a faulty exhaust manifold, most of them may appear due to other exhaust system problems. Thus, a loose exhaust manifold bolt or a broken exhaust manifold gasket can lead to similar symptoms. The other source of the problems can be a faulty oxygen sensor or exhaust gas recirculation valve attached to the exhaust manifold.
Exhaust manifold troubleshooting
An exhaust manifold is a maintenance-free part that must be replaced if it fails. As a rule, it doesn’t cause damage to other parts and components under the hood. However, rarely, it can lead to a premature failure of the catalytic converter or the cylinder head. Besides, exhaust smoke and odors can enter the cabin while you’re driving.
Unless you’re a mechanic, the replacing procedure should be done by a professional because it often involves specific equipment and lots of labor.