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Discussion Starter #1
99 Eld

What is the logic sequence in regard to conditions required for pulling vacuum on the fuel tank? I notice that the purge valve does not begin operation until a short time after engine start. Is this a timed delay or is it waiting for a specific signal from the tank pressure sensor? Is the vent solenoid used to maintain a tank pressure band or limit, as necessary, during operation? What is that band or limit?
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Purge normally begins during an extended moderate speed highway cruise - when the slight extra air added to the intake charge will not affect driveability. Purge should never occur at low speeds, in N or P, or at idle. I believe the fuel filler cap has a pressure seal and a low vacuum relief. Fuel always recirculates from the fuel rail back to the tank - matter of fact, more fuel returns to the tank than is burned because that pump moves a LOT of fuel. The tank operates at almost atmospheric pressure due to the timed/pressure/vacuum operation of the purge and tank vent solenoids.
 

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Discussion Starter #3 (Edited)
I have a P0452 (Fuel Tank Pressure Sensor Circuit Low Voltage) code. I noticed that my vent solenoid is open all the time. Vacuum from the engine to the canister is good but it is always pulling atmosphere, not the tank. I removed the vent valve, shook it and realized the valve was stuck, or so I believe. I "coaxed" it a little bit to the point where the valve unstuck (I believe) but it is still open while plugged in and engine running. On the other hand, my purge valve is consistently in full operation by 20-30 seconds after start up. Could a bad tank pressure sensor be throwing off the normal operation for these other devices? I have confirmed that the tank is sealed tight by blocking off the vent tube during purge valve operation. Low voltage at this sensor would mean high pressure, I would think the system would try to compensate by pulling vacuum on the tank and put the vent valve into the closed position.

FWIW, since I started having this code I have filled up twice and the code disappeared for ~50 miles the first time and ~15 miles this second time.
 
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