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97 Ford Expedition codes P0171 and P0174 not a PCV leak

Model: 97 Ford Expedition Fault Code: P0171 Posted: 2009-02-18 18:25

I have 97 Expedition 5.4L 4x4 154k miles with 2 codes: P0171 and P0174. has new vacuum hose from intake to PCV, not leaking there. I don't hear any hissing fuel pressure is 30 lbs. long term fuel trim is 19% on B1 and 14% on B2 at idle. short term stays near 0%. at 2500 rpm short and long are less than 5% which leads me to believe it does have vacuum leak. I have sprayed carb cleaner all over and haven't been able to get short term to change. are there any other likely vacuum leak areas to check? do the intake manifold gaskets leak? I would appreciate any help. thanks Statty

Related fault codes
P0171P0174
Comments (4)
Anonymous 2009-02-18 20:50

I had this issue with my 97 exp as did my brother with his. If you reach over the top of your engine behind the intake dead center of the window, there is a 90' rubber elbox that I bet you has a hole . I got the replacement for ~ 3$ from the HELP section in Advance Auto . This problem drove me nuts for a couple three weeks... good luck curtis

Anonymous 2009-02-19 11:37

thanks Curtis but that is the vacuum supply to the PCV. I replaced that about 8 months ago for this same issue and it solved but now i am getting the same codes and that hose is fine. any other suggestions? statty

Anonymous 2009-02-19 13:14

On the way to my fix, I did clean then replace Mass Air Flow Sensor, that did nothing, I used wd40 all over the intake seams and got no result, checked for exhaust leak between exhaust manifold and rear 02 , pulled a vacuum check on the pcv hose, ( that is when i found the elbow in back of intake) .. I am out of ideas but I am sure alldata has a check list.. I wish you the best... curtis

Anonymous 2009-02-19 16:56

That fuel pressure is just at the acceptable minimum (30-45 PSI @ KOEO). Check it at idle. It should be 27-42 PSI. It could be fuel pressure regulator, fuel filter or the fuel pump going south. The intake manifold gaskets do leak, but both at the same time? Seems strange to me. If fuel pressure is OK, I'd be checking/cleaning the MAF and checking for any unmetered air entering the engine, particularly between the MAF and Throttle Body as well as re-checking all vacuume lines (including Brake Booster). Good luck and keep us posted.