pcv valve and p0171/p0174 issues

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Rich Lacilla

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Joined
Nov 29, 2006
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Location
Thomaston , CT
Hello All,

I have a 2003 trac with 240,000 miles and job 2 engine. I've had this vehicle for 12 years and it doesn't owe me a dime, virtually trouble free except for the p0171/p0174 issues. The truck still seems to run fine, maybe I've been driving it so long i just can't tell.

Anyway, I've been chasing the p0171/p0174 issue for years and haven't been able to figure it out, despite all of the great info on this forum, but maybe I just found something.



So far I have:

Changed the infamous cracked elbow (wasn't cracked) a few years ago, just pulled it off again and checked it again(still not cracked)

Replaced PCV valve a few years ago when I changed the PCV elbow and hose

Replaced the MAF sensor last summer,

Had intake manifold gaskets replaced twice over the course of last 4 years, most recently 2 years ago by a local garage(no longer in business), passed emissions, CEL came on as I was driving away from testing center.

Just replaced sadly worn plugs and wires out of desperation last week (first time replaced ever).



While checking the elbow again tonight I noticed the PCV valve was loose and able to come out.

It wasn't like that when I put it in a few years ago. I know that it locks in and that it can't be removed without replacing it. Maybe it came loose with the various mechanic working on it.



Anyway, can a loose PCV valve cause the p0171/p0174 codes. I'm inclined to believe so. Also is it possible that an oil leak in the left valve cover can cause those codes. I tend to do all of my own maintenance on my truck if it's in my skill level because finances are tight.



BTW, it's emission test time again for me and I need to get it thru again. Does anyone have any thoughts?
 
Rich, I have had oil leaks in both cam covers and didn't through any code! You can eliminate that.

Ed
 
Had the same issue with the driver side valve cover oil leak caused by a loose PCV valve, but didn't have lean codes. I believe my valve cover "'nubs" were broken off from the original owner over tightening. I read the only fix was replacing the valve cover, but instead bypassed the coolant hose using oil resistant RTV to seal the PCV valve. Years later no oil leaks. I'd give it a try, lot's of vacuum going through the PCV valve. Can post working pics if you'd like.
 
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My 04 with 190k had the same issues and I did the same repairs as above. My last repair was the o2 sensors and cat. After that, no more codes.
 
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