Question about 2003 Ford Explorer Sport Trac

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2003 Ford Exployer Sport Trac\r\nMy check engine

2003 Ford Exployer Sport Trac My check engine light keeps coming on, the reader shows codes 171 and 174.
I've done the following:
1. Replaced Gas Cap
2. Use high octane gas and added STP to clean jets
3. Replace the Mass Airflow Sensor
4. Replace all 3 Oxygen Sensors
I'm at a loss, what do I do now?

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1. Trouble code P0171 means: Fuel System Too Lean (Cylinder Bank 1)
2. Trouble code P0174 means: Fuel System Too Lean (Cylinder Bank 2)
Not to replace the Valve cover that Ford just recommends it. The only difference is the hole where the PCV vavle goes is different. Replacing would have nothing to do with the code and the vehicle not running good. You only needed to replace the Bolts and of course the seals. The bolts are $6 each, $48 for just the bolts and another $17 for the Seals. Remove intake manifold.
The improved valve cover does not eliminate the oil in the intake problem, it does reduce it. Replacing especially since the TSB is very specific about needing to replace it (quote from TSB "VALVE COVERS FITTING THIS DESCRIPTION MUST BE REPLACED"). The cause of the P0171 and P0174 problems is caused by the oil getting into the intake and being absorbed by the rubber grommets on the bolts. That's why they have a redesigned bolt, by the way verify that the bolts they gave you had green grommets on them and not black. Unfortunately they kept the same item number even though they are different. So with the improved bolts and new seal you probably won't see the leak again, but by not reducing the oil going into the intake you may see the clogged EGR ports and deposits in the combustion chambers sooner than with the improved valve cover which could lead to pinging.

The reason you get the 171/174 codes is because air is getting into the cylinders from another source other than through the throttle body so the computer does not "know" about it. This is a vacuum leak and when the Isolator bolts stop functioning it allows air to enter from the Upper to Lower intake manifolds via the port seals.
The problem is most likely the intake-manifold gasket.

Posted on May 11, 2010


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Very common concern with the Explorer, Explorer Sport Trac and Ranger with the 4.0l SOHC engine! The upper and lower intake manifold gaskets fail, causing vacuum leaks..It can be Extremely difficult to detect these leaks, because they only leak intermittently (usually in the AM after a cold soak)... As the engine warms up they seal back up! Sometimes the vehicle will idle rough, surge or stall after initial start up, then the symptoms will clear after it gets to operating temperature... Usually there will be no driveability symptoms at all, except the engine light coming on and setting lean codes.. The gaskets have been redesigned to correct this concern..

Bill Andrade Ford Master Technician/ASE Master Technician

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Check engine light on computer codes 171 174 171-HEGO sensor unable of snitch cylinder bank #1 fuel system at adaptive limit (1990 on) code 174 hego sensor snitching too slow, cylinder bank #1 (1990)

switch, we run off snitches. 171 174 banks 1 & 2 Lean. Most likely cause are Upper Intake Manifold Gaskets, failed seals. It's not 1990 on. It's 1996 and on OBD2.

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