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vapor94vmv.jpg | Hits: 300 | Posted on: 2/18/24
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Vapor Management Valve (VMV) replaces CANP on some '94-95 & all '96 trucks under 8500GVWR
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The EVAP Vapor Management Valve (VMV) is the part of the Vapor Management Flow system that is controlled by the PCM. This valve controls the flow of vapors (purging) from the EVAP canister to the intake manifold during various engine operating modes. The EVAP canister purge valve is a normally closed valve. The Vapor Management Flow system consists of a fuel tank, fuel filler cap, fuel vapor valve, EVAP canister, Vapor Management Valve (VMV), intake air tube assembly, powertrain control module (PCM) and connecting wires and fuel vapor hoses. Operation of the system is as follows:
1. The Vapor Management Flow system uses inputs from upon the engine coolant temperature (ECT) sensor, the intake air temperature (IAT) sensor, the mass air flow (MAF) sensor and the vehicle speed sensor (VSS) to provide information about engine operating conditions to the PCM. The conditions necessary to activate the Vapor Management Flow system is that the engine must be warm, stable, running at a moderate load and rpm, at open or part throttle position, and in close loop fuel control. The PCM deactivates the fuel vapor management flow during idle or whenever a failure is detected in the EVAP canister purge valve or fuel vapor management flow required input.
2. The PCM calculates the difference between the idle speed air requested at a high purge flow and at a no purge flow. If the difference is below a calibrated threshold, flow is inferred not to be occurring properly, and the PCM indicates an evaporative emission system malfunction with a Diagnostic Trouble Code (DTC).
3. The PCM outputs a variable duty cycle signal (between 0% and 100%) to the solenoid on the EVAP canister purge valve.
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