P0171 & P0174

[Tempest]

99' Ford Ranger 4.0 manual trans. ~108K miles. 2WD.

Codes are lean Bank 1 and 2.
According to the Innova 3130 that I just bought (new to using scanners) freeze frame shows info for P0171:

Fuel system = CL

Calc Load = 24.3

ECT = 172F

STFT B1 = -4.6

LTFT B1 = 17.1

STFT B2 = -3.9

LTFT B2 = 17.9

RPM = 1662

Speed 12 mph

This has been on going for a while. I've: changed the air filter, changed both up stream O2s, checked the fuel pressure at the rail (idle) and it is right on spec, checked the MAF power input and it is at spec., cleaned the MAF with electrical cleaner, fuel filter was just changed about 1 year ago, the engine changes how it runs if the MAF is unplugged (should be good MAF?) (will not throw a code!), run a bottle of Regane through it, and sprayed around the engine with carb cleaner to check for vacuum leaks...still nothing that I can find at fault.

Any help or ideas on this would be much appreciated.

 

[Colt45ws]

It should throw a code for a MAF fault on the second key cycle. At least thats what my Ford did when I left it unplugged accidentally.
Can you monitor PIDs with that?

 

[kaboom10]

Those codes show the LTFTs are at max. The ECM is compensating for a lean condition common to both banks. Most likely it's a hose that is leaking. The 5.4s hace a vacuum huse that goes to the back of the throttle body down spout to the intake. Ck and maybe replace the PCV also. Get some carb cleaner and spray it around a running engine to see if the idle speed increses.

 

[punisher]

You either have a vac leak or a MAF problem, with low fuel pressure coming in a distant third as far as causes.

Get your data stream set up and monitor fuel trims at idle. IF they are lean at idle, you have a vac leak. Rich trims at idle that go lean during acceleration/open throttle= bad MAF.

4.0 SOHC were notorious for intake leaks. The intake gaskets are a set of O-rings for upper and lower. The old gaskets are pale green, the updated replacements are blue. Agree with above, shoot some carb cleaner around the base of the intake, upper-lower intake joint and see see if the SFT shifts. Gasket replacement is an easy job, it is a dry manifold so no coolant to drain.

EDIT: FoMoCo might have a program/addl warranty coverage for this concern.

 

[UNC038]

Vacuum leak. Spray with carb cleaner while monitoring STFT & LTFT, this will help you find it.

 

[Tempest]

Thanks guys. My scanner will monitor PIDs, the main reason I got it.

This 4.0 is the older OHV, not the SOHC.

I have sprayed everything that I can think of with carb cleaner and there hasn't been any obvious change in the way the engine runs, but that was before I got the scanner. I guess I'll have to give it another try and watch the trims.

 

[FowVay]

It's definitely a air leak judging by the long term fuel trim numbers.

There's a small plastic tube on the left side of the manifold that has a 90º elbow that will split and allow air into the manifold. I have replaced a half dozen of these on the sport trac Explorer and the Ranger pickups.

It's up near the front of the engine and on the left side. I wish I were better able to describe the location. Spray some ether in the area and you'll immediately hear the engine rev.

Good Luck!

 

[SZR48207]

Is the 4.0L a I6 or V6? I think I saw something about this on the Explorer Forums where a guy replaced the lower and upper intake manifold gaskets for his late 90s Explorer. From what I read, it is a common problem with high mileage, but the job isn't too difficult. I'll see if I can find the thread.

Also, you may check your PCV valves and any rubber elbows that connect to them. Seems like it is common for holes to develop in the rubber elbows, causing intake leaks.

 

[SZR48207]

Here's the thread on replacing the intake manifold gaskets.

http://www.explorerforum.com/forums/showthread.php?p=1555157