5.4L with P171 and P174 check engine codes
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5.4L with P171 and P174 check engine codes
The P171 and P174 codes are defined as a lean left bank and lean right bank in most auto manuals. These are common codes across all auto makes. AutoZone has a program whereas they will check your "CHECK ENGINE" codes and try to help you solve the problem. I ended up at a Ford dealership after a visit to AutoZone and found the following to be the source of the problem causing the P171 and P174 codes.
I have a 1998 F-150 with the 5.4L that had both of these codes. The trouble turned out to be a bad PCV hose fitting that had developed a crack in it resulting in a vacuum leak after the mass air flow sensor, MAP sensor. The vacuum leak on the intake manifold caused the computer to enrich the fuel to air ratio and as a result, a lean oxygen content at the oxygen sensors on both the left and right banks of the exhaust manifold.
The PCV valve is in the passenger side valve cover on the engine, the hose routes to the back of the engine where a 90 degree fitting fits into the intake manifold. The 90 degree rubber fitting developed a crack on the inside of the 90 degree turn. This is not obvious until the fitting is removed for inspection.
The PCV valve, hard plastic hose, and 90 degree rubber fitting are sold as a unit for around $20 at a Ford dealership.
The cause of this crack, in my opinion, is either a defect in the fitting material or design of the connection itself. The PCV valve and hose passes hot combustion gases into the intake to be burned in the engine. These gases contain gasoline, oil, and other combustion by-products that can deteriate rubber fittings that are not up to design for such.
There are other sources for P171 and P174 codes. This just happens to be what happened in my case. But if you are getting BOTH of these codes, it is very likely there is a vacuum leak somewhere in the intake manifold after the mass air flow sensor.
I have a 1998 F-150 with the 5.4L that had both of these codes. The trouble turned out to be a bad PCV hose fitting that had developed a crack in it resulting in a vacuum leak after the mass air flow sensor, MAP sensor. The vacuum leak on the intake manifold caused the computer to enrich the fuel to air ratio and as a result, a lean oxygen content at the oxygen sensors on both the left and right banks of the exhaust manifold.
The PCV valve is in the passenger side valve cover on the engine, the hose routes to the back of the engine where a 90 degree fitting fits into the intake manifold. The 90 degree rubber fitting developed a crack on the inside of the 90 degree turn. This is not obvious until the fitting is removed for inspection.
The PCV valve, hard plastic hose, and 90 degree rubber fitting are sold as a unit for around $20 at a Ford dealership.
The cause of this crack, in my opinion, is either a defect in the fitting material or design of the connection itself. The PCV valve and hose passes hot combustion gases into the intake to be burned in the engine. These gases contain gasoline, oil, and other combustion by-products that can deteriate rubber fittings that are not up to design for such.
There are other sources for P171 and P174 codes. This just happens to be what happened in my case. But if you are getting BOTH of these codes, it is very likely there is a vacuum leak somewhere in the intake manifold after the mass air flow sensor.
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dhenthorn
1997 - 2006 Expedition & Navigator
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Jun 28, 2011 06:07 PM
Lugnut2008
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Nov 9, 2007 01:57 PM
