I bought a 1997 Explorer recently and when the weather cooled off I started getting the dreaded P0171 & P0174 OBDII codes. No other pending codes, no incompletes, and all sensors operating correctly. I did alot of searching on this and other forums and thought I would consolidate my findings here.

The 1997 Explorer had two 4.0 engine options. Check the eighth digit of the vehicle VIN number, if it's an "X" then you have the OHV engine.

The P0171 and P0174 OBDII codes are lean bank 1 and bank 2. This typically is a good indicator that there is a vacuum leak or unmetered air entering the engine after the MAF sensor. I checked the easy things like cleaning the MAF and making sure the air intake duct didn't have any cracks and was connected properly. To make a long story short I ended up removing the plastic intake manifold down the injectors and replacing all of the gaskets from the injectors up. The plastic intake manifold is prone to air leaks where it mates to the fuel injector log.

Obtain the following gaskets.

F57Z-9E436-AA QTY 3
F6TZ-9E436-C QTY 1
95TZ-9E936AA QTY 1
957Z-9F670-AA QTY 1
FOPZ-9229-A (These come in a pack of 10 and you need 12 so buy two packs. They are the o-rings for the fuel injectors)
E6AZ-9D476-B QTY 1


If I was doing the job again I would obtain the O-ring for the EGR tube where it mounts into the plastic air intake. The most challenging part of this job was getting the EGR disconnected from the intake. I ended up unbolting the EGR tube from the EGR valve and pulling the intake with the EGR tube attached. Once on the bench I was able to seperate the tube from the intake. The o-ring holds the tube.

 

EGR info...

 

replace upper intake manifold gaskets ,maf,o2sensors,truck runs fine while in the closed loop mode,afterwarmup engine idles erratically and stalls

 

The CPM enters closed loop when the engine and O2 come up to temperature... Please clarify what the issue is...

Have you connected a LIVE DATA SCANNER?? .... Philip

 

getting code 171/174 replaced upper intake manifold gaskets,maf,upstream and downstream 02sensors still getting code 171/174 runs fine while in the closed loop mode ,idles erratically and stalls after warmup while idling

 

Lower intake maybe leaking, check gasket at manifold to head.

Injector o rings may need inspection too.

 

Please remember to check the easy things first when getting both P0171 and PO174 codes together with no other codes or errors. There is unmetered air entering the engine past the MAF causing the lean condition. Culprits are: EGR, Vacuum Lines, PCV, PCV Hose, Intake manifold gasket to Head, Intake Manifold to Fuel Log "o-"rings, Fuel Log to Intake Manifold gasket, Oil Cap, Oil Tube Vent Hose, Intake hose from air filter, etc...

 

I had the same problem with my 98 ford 4.0 ohc exp.237,000 miles. It was upper intake manifold gasket and o-rings.