PCV Valve
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Senior User
Joined: Feb 2016
Posts: 306
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From: Winchester, VA
PCV Valve
My 2004 Ex started life in Arizona. From looking at the PCV valve, I don't see any wires running from it, so I assume it's unheated. Is it worth replacing it with a heated valve since it lives in an area that gets freezing temperatures or is the Motorcraft EV270 standard valve OK to run in cold weather? The reason I'm asking is because I got a check engine light with P0171 code the other day. I was planning on cleaning the MAF first and thought I might go ahead and replace the PCV while I was at it. The truck has 64000 miles on it.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,812
Likes: 88
From: Thousand Oaks, CA
I don't know if the 2004 has the electric heated PCV valve, but our 2002 is heated with a 1/4" engine coolant hose. If the fitting on the intake for the heater hose has a capped off 1/4" hose port someone may have removed the PCV coolant hose. The PCV valve has a calibrated spring inside which can go bad or it can get gummed up inside. Ours has 110k and is still working fine.
Check the PCV hose elbow behind the throttle body, the elbows rot out and leak. I replaced ours with sections of reinforced fuel hose and a brass elbow. The P0171 is a bank 1 lean code and can be a vacuum leak in any vacuum hose, not just the PCV hose. A leaking brake booster diaphragm or vent control line would still be a vacuum leak. Could also be a bad O2 sensor. Several other vacuum lines on ours were in poor condition so they were replaced with silicone vacuum hose. Cleaning the MAF might fix the problem, clear the code and drive it awhile to see if it comes back.
Check the PCV hose elbow behind the throttle body, the elbows rot out and leak. I replaced ours with sections of reinforced fuel hose and a brass elbow. The P0171 is a bank 1 lean code and can be a vacuum leak in any vacuum hose, not just the PCV hose. A leaking brake booster diaphragm or vent control line would still be a vacuum leak. Could also be a bad O2 sensor. Several other vacuum lines on ours were in poor condition so they were replaced with silicone vacuum hose. Cleaning the MAF might fix the problem, clear the code and drive it awhile to see if it comes back.
Last edited by R&T Babich; May 22, 2016 at 04:44 PM. Reason: Removed reference to Az, saw it's now in Va.
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