Could it be that the ecu is wrong

P0450 Evaporative Emission Control System Pressure Sensor ...

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P0450 Evap Emission System Pressure Sensor Malfunction ... This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to ...

P0450 OBD-II Trouble Code: Evaporative Emission Control ...

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P0450 is a diagnostic trouble code (DTC) for "Evaporative Emission Control System Pressure Sensor Malfunction". This can happen for multiple reasons and a ...

P0450 - Evaporative emission (EVAP) pressure sensor ...

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Nov 18, 2015 - The code P0450 is set when the ECM reads a voltage signal lower than ... DTC P0453 Evaporative Emission Control System Pressure Sensor ...

13C-DTC P0450: Evaporative Emission Control System ...

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DTC P0450: Evaporative Emission Control System Pressure Sensor Malfunction. CIRCUIT OPERATION. The ECM (terminal No. 114) supplies a 5 volts ...

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1.1 Engine Control Unit (ECU); 1.2 Immobilizer (integrated in Instrument Cluster); 1.3Immobilizer (integrated in separate Immo Box); 1.4 Immobilizer (integrated ...

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The EVAP (Evaporative Emissions) System allows fuel tank vapors to be purged into the engine and burnt rather than expelled into the atmosphere as harmful emissions. The EVAP system contains a pressure sensor to check the integrity of the system. Periodically, the EVAP system performs a pressure test to check that there are no leaks in the system. It uses this sensor, also known as a fuel tank pressure (FTP) sensor to check for leaks. Basically P0453 means the PCM (Powertrain Control Module) noticed the EVAP Pressure sensor or FTP is indicating a higher than normal pressure (above 4.5 Volts) in the EVAP system. NOTE: On some vehicles the FTP is a part of the fuel pump assembly in the tank. Potential Symptoms There will likely be no noticeable symptoms along with this code other than the MIL (Malfunction Indicator Lamp), commonly known as Check Engine Light illumination. However, there may be noticeable fuel odors in some cases. Causes A P0453 DTC trouble code may be caused by one or more of the following: Open on FTP sensor signal wire Short to voltage on FTP sensor signal wire Bad FTP sensor Abnormally high pressure in fuel tank due to blockage in EVAP purge hoses or overfilled tank Loose/damaged FTP sensor connector Loss of ground to the sensor Possible Solutions Using an scan tool access FTP sensor value with Key on Engine off (KOEO). Normal value is usually somewhere near 2.5 Volts at atmospheric pressure (may fluctuate some due to altitude). It shouldn't ever be above 4.5 Volts. 1) If it is close to 2.7V with the gas cap off, the problem is likely intermittent. Using a Digital Volt Ohm Meter, measure the voltage on the signal wire while trying to induce the problem by wiggle testing all the wiring at the FTP sensor. If the voltage fluctuates when wiggle testing, check for connector problems; i.e. water in the connector, broken or chafed wiring. 2) If the value shown on the scan tool is above 4.5V, unplug the sensor (if possible) and check for voltage again. If the high voltage is still present when unplugged, inspect wiring harness for a short to voltage on the signal wire. If the high voltage disappears when unplugging the sensor, check for a good ground to the sensor and proper reference voltage. If you have a good ground and 5 Volts reference voltage, replace the FTP sensor since it's likely shorted out. Other EVAP DTCs: P0440 - P0441 - P0442 - P0443 - P0444 - P0445 - P0446 - P0447 - P0448 - P0449 - P0452 - P0455 - P0456

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Air filter, ECU, O2 sensor, bad EGR valve, or clogged cat converter.

Onboard diagnostic computer should be throwing codes. Autozone can check these free (as will other part stores).

Here is the definition.

The Code P0450 indicates that the Evaporative Pressure Sensor output value is not changing during the EVAP Monitor test and/or the operation of the vehicle. This code uses "two trip" logic, which means that the fault condition must be present during two successive cold starts and vehicle operation.
The sensor is mounted in the top of the gas tank near the sending unit. You would need to test the pressure sensor.

pull the backup fuse in the fuse box under the hood near the battery.

You might want to check the ECU of the engine that u swapped it to. Because the original ecu is only for the 1.4L non vtec!!!

The 96-98 Civic EX came with an OBD2A D16Y8 engine. That is the only engine that will go in as a direct replacement with your current engine ECU. It's an SOHC VTEC engine that has two extra connections not found on the other 96-98 Civic engines - a VTEC solenoid and a special oil sensor used to determine if VTEC engagement is possible. If you swap in an older Civic engine (92-95 generation) you'll have to convert the car to OBD1 (requires a special adapter hardness) and run the ECU that goes with whatever engine you use. This will break functionality of your OBD2 diagnostics port, and depending on which state you live in will cause you to fail emissions checks. If you install a D16Y8 engine from a 99-00 Civic EX, you will have to swap the intake and exhaust manifolds from your old engine to the new engine, and you will be able to continue to run your existing OBD2A wiring and ECU. The 99-00 Civic EX engines have additional sensors, since those engines are OBD2B. The easiest fix would be to find a SOHC VTEC D16Y8 from a 96-98 Civic EX, as it would be a direct plug and play replacement.

run scanner for trouble codes, some auto parts stores   will do this for free

it means your 02 sensor pre cat is not working or the cat is no longer any good start with the 02 sen its easy to do and cheaper than the cat