Help me diagnose this problem?

[Lebult]

Hi everyone,
I recently inherited a 2001 Ford Explorer XLS 4x4 Auto (4.0 SOHC) from my dad, and it has a bunch of little problems.
The one that really concerns me is that terrible gas mileage. It's getting about 5.5kms to the liter (12mpg or so), and I'm convinced that's not right.
I've been scouring through all of the Explorer and Ranger forums I could find over the last couple of months, trying to figure out what could be causing the problem, but now I think it's time I try posting here, and give the Explorer Gurus a crack at it.

Known problems/Potential symptoms ;
- It's getting P0171 and P0174 error codes
- Coolant is not reaching optimal temperature (replaced Thermostat, but no change)
- Bank 2 O2 Sensor appears to be stuck at 1.3 volts. Bank 1 O2 Sensor fluctuates normally from 0.2v to 0.7v
- Long Term Fuel Trim on both banks sits around +/- 2% during normal driving, but hovers around +12% to +14% when idling
- Cold starts cause engine stuttering. Almost certain it's the IAC, despite trying clean it (And the MAF). Not sure if that's relevant.

I'm guessing it could be a number of things, from a wrecked intake gasket, to a vacuum leak (PCV elbow? haven't checked yet), etc etc.

My question to you guys is, what else should I be looking at?
What should my vacuum be at idle?

I'm pretty sure that O2 sensor needs to be replaced regardless, so I'll do that asap. Bank 2 is driver side on the 4.0 SOHC Explorer, correct?

 

[drdoom]

Yes bank 2 is drivers side. I think you are on the right track, definitely do the O2s and check for vacuum leaks. Replace the fuel filter if it has been a while (not really a fix, but necessary and worthwhile).

 

[jremington59]

Have you tried cleaning the MAF sensor? With the rough idle at start up, along with the two codes you may need to change the intake gasket. I'd try the MAF cleaning first.

 

[JusTheUsual]

sick of hearing "intake gasket" my experience, either fuel pump/filter or blown head gasket, worked on enough of them to know. never ever had a intakes gasket gone, always the fuel pump or filter or blown headgasket

 

[jremington59]

sick of hearing "intake gasket" my experience, either fuel pump/filter or blown head gasket, worked on enough of them to know. never ever had a intakes gasket gone, always the fuel pump or filter or blown headgasket

Well my experience, and I've owned enough of them is with the two codes and the rough idle at warm up is the intake gaskets. Once it warms up the rough idle will stop. But you could be right. The guy asked for suggestions. Just out of curiosity, how would a "blown head gasket" trigger those two codes?

 

[Lebult]

I suspected the head gasket as well, but replacing that is not an option, so I'll try the less expensive paths first.

Can someone with a healthy engine and a live data scanner share what their Vacuum level is at idle ?

Would a bad fuel pump cause it to use more fuel than normal ?

 

[swshawaii]

The PCV elbow should be the FIRST place to check for p0171-174 DTC's on the 2001-03 2-Door Sports and Job 2 ST's.

http://www.explorerforum.com/forums/showthread.php?t=314670

 

[Lebult]

New information;

I've discovered that BOTH post-cat o2 sensors are not working correctly.
Bank 1 is stuck at 0.8v, and Bank 2 is stuck at 1.3

What could cause both sensors to go bad? Could it have something to do with the cat?

 

[deadernie]

Coolant never reaching proper temperature will cause fuel mixture to bigger rich which will not help your fuel mileage at all.

 

[Lebult]

The live scan tool is telling me it's capping at 88 degrees C, which is about 190 farenheit. I could swear the OE was 192 but correct me if I'm wrong. I have to replace the intake manifold gaskets, so maybe I'll swap that sensor at the same time.

 

[drdoom]

I havee had both post cat sensors fail within a few thousand miles, but I don't think it was caused by anothing other than 190,000 miles.

 

[bill06447]

Ford has a TSB on engines with those two codes, go here for a step-by-step before you start throwing money at parts needlessly. The PCV elbow/modified valve cover as previously mentioned, is the first step along with the vacuum leak checks http://www.aa1car.com/library/ford_lean_codes.htm

Bill