Lexus 25051-20040 Exhaust Manifold Converter Sub-Assembly

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Before lifting the exhaust manifold, the first thing that should be done is to disconnect the cable of the battery's negative terminal. Lift the front of the vehicle and set it on jackstands safely and then, take off the lower splash shields and front floor cover from the left side. Pry these bolts loose while being very careful not to remove the oxygen sensors by applying penetrating oil on the bolts that hold the exhaust pipe to the manifold and allowing them to soak before removal. Unfasten the exhaust neck from the manifold, undo the down exhaust manifold girders, and unsnap the connectors on the oxygen sensor. Situated in the engine compartment, it is necessary to take off only the upper heat shield from the manifold while observing that the last type of heat shield is not required to be detached. Remove the nuts/bolts and take off the manifold along with its gasket. For installation you will use a scraper to scrape the mating surface of the manifold and cylinder head cleaning it and during this process you will check for warpage if the gasket is in bad state and it is leaking. If changing a manifold only, bolt the lower heat shield onto the new one. Place a new gasket over the studs on the cylinder head and ensure the manifold is fitted Thread the mounting nuts starting with the middle one before you tighten all of them. Replace the rest of the parts in the reverse order you removed them, starting the engine to check for leakages through the exhaust.

Regarding catalytic converters, it's worth noting that due to a mandated extended warranty covering emissions-related components, it's advisable to consult a dealer service department before replacing the converter at your own cost. The catalytic converter, an emission control device in the exhaust system, reduces pollutants. There are two types: the oxidation catalyst, which reduces hydrocarbon (HC) and carbon monoxide (CO) levels by adding oxygen to the exhaust stream to produce water vapor (H2O) and carbon dioxide (CO2), and the reduction catalyst, which lowers oxides of nitrogen (NOx) levels by removing oxygen to produce nitrogen (N) and oxygen. The two types are combined into a three-way catalyst. Proper oxygen levels are vital for its operation, as it captures and stores oxygen most efficiently when converting exhaust gases mixed at the ideal air/fuel ratio of 14.7:1. Lean or rich air/fuel ratios can impact its function. The PCM monitors the catalyst's oxygen content via upstream and downstream oxygen sensors. If it's not working, the downstream sensor indicates elevated oxygen, prompting a Diagnostic Trouble Code (DTC) and the Malfunction Indicator Light (MIL) activation. Checking the converter requires specialized equipment, but you can check for restricted converters using a vacuum gauge to diagnose the effect of a blocked exhaust on intake vacuum. If damage is found, replacement is necessary. Upstream catalytic converters are integral to the exhaust manifold. Replacement procedures vary by model year and engine type. Always ensure the catalytic converter has cooled before servicing.

Regarding catalytic converters, it's worth noting that due to a mandated extended warranty covering emissions-related components, it's advisable to consult a dealer service department before replacing the converter at your own cost. The catalytic converter, an emission control device in the exhaust system, reduces pollutants. There are two types: the oxidation catalyst, which reduces hydrocarbon (HC) and carbon monoxide (CO) levels by adding oxygen to the exhaust stream to produce water vapor (H2O) and carbon dioxide (CO2), and the reduction catalyst, which lowers oxides of nitrogen (NOx) levels by removing oxygen to produce nitrogen (N) and oxygen. The two types are combined into a three-way catalyst. Proper oxygen levels are vital for its operation, as it captures and stores oxygen most efficiently when converting exhaust gases mixed at the ideal air/fuel ratio of 14.7:1. Lean or rich air/fuel ratios can impact its function. The PCM monitors the catalyst's oxygen content via upstream and downstream oxygen sensors. If it's not working, the downstream sensor indicates elevated oxygen, prompting a Diagnostic Trouble Code (DTC) and the Malfunction Indicator Light (MIL) activation. Checking the converter requires specialized equipment, but you can check for restricted converters using a vacuum gauge to diagnose the effect of a blocked exhaust on intake vacuum. If damage is found, replacement is necessary. Upstream catalytic converters are integral to the exhaust manifold. Replacement procedures vary by model year and engine type. Always ensure the catalytic converter has cooled before servicing.

Remove the heat shield from the front exhaust manifold.

Run the engine and check for exhaust leaks.

Raise the front of the vehicle and support it securely on jackstands, then remove the engine splash shields.

Apply penetrating oil to the bolts retaining the exhaust pipe to the manifold. After the bolts have soaked, remove them and lower the front exhaust pipe, being careful not to damage the oxygen sensors.

Yes, the following procedure applies to either exhaust manifold.