P0171 Lean Issue

[Tim Hoberock]

I have a 2001 Sport Trac with ~120K miles on it. It is throwing a P0171 and P0174 Trouble code (lean fuel condition). It has a new MAF sensor, so that's not the issue. Here's what I have found on this site (and the web) as possible causes:



- MAF = OK

- PCV Elbow = OK

- Fuel Filter = Will replace tomorrow, but I don't think that's it

- PCV Valve = Maybe

- DPFE sensor = Unlikely, I would expect to see P0401 code as well

- Vacuum Leak = Inspected all the line and found nothing



Any other ideas? I see that some folks have had this issue, but I don't see how they resolved it. Can some who had this issue (and fixed it) please chime in?



Thanks,

Tim

 

[Jason Cronin]

oxygen sensor. It part of the system that controls the air to fuel ratio. Its located on each exhaust pipe after the manifold. Start with that. Its also A good idea after changing out parts the disconnect the battery for about 15 to 20 minutes to clean out any codes andd reset the computer. I would do that first, then drive it to see if the code comes back.

 

[Doug Watts]

Make sure you check this vacuum elbow. The crack is always on the bottom.



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[Richard L]

I agree with Doug Watts. The vaccum elbow is a notorious source of the Lean condition for Sport Trac's. I still think you have a vaccum leak and sometimes a visual inspection will not find it. I always use a small propane tank (for a torch) and a hose and move it around all the vacuum lines and intake while the engine is idleing. As soon as the gas is sucked into a vaccum leak you will hear the engine idle speed up noticably...That's your leak. Just do this in a wel ventilated place or outside if there is no wind.



...Rich

 

[Cesar Macias]

I just got the same thing and I checked and it's that elbow. What's the name of it? Or does anyone have the part number so I can pick it up at autozone, ford, etc...



Thanks,

Cesar

[email protected]

 

[Kevin Palmer]

Here is the part and part number...



Also, Tim, you may not have this elbow as you have a 2001. Is your Trac a Job 1 or Job 2?



Job 1 will NOT have this elbow. There is common fix for the Job 1 but I do not recall what it is off hand..

 

[scott degroot]

Ok heres the deal. If you are throwing lean codes for both banks and the maf is good and the infamous pcv elbow is ok then you need to start looing for other issues that affect both banks. While an oxygen sensor can cause a lean code both oxygen sensors would have to be bad to casue both banks to go lean, it is possible but highly unlikely that both oxygen sensors went bad at the same time. The next thing to check is fuel pressure, low fuel pressure will cause both banks to run lean but will almost certainly also cause a very noticeably loss of performance. If I was a betting man I would put my money of you having a leaking intake manifold gasket, upper, lower or both. Problem is that if the manifold is leaking vacuum it will be hard to detect without the use of a scanner being that the pcm has such tight control. What I do is look at the fuel trims while introducing propane around the sealing surfaces of the manifold. When you find the leak the fuel trim numbers will instantly start going negative but you may not necessarily hear a change in the way the engine runs due to the pcm control, this is what makes it hard to detect without the use of a scanner and live data. Alot of people will use carb spray adn spray the sealing surfaces but I have learned from experience that the spray can and will soak into the intake and cause a false reading.



On a side note using a scanner is the only real way to verify the maf on a Ford. You have to look at the Baro reading which is calculated by the maf. When the maf's go bad they skew the baro reading adn make the truck believe that it is at a different altitude than it actually is , this throws the fuel control way out of whack. You can put in a new maf but it still may not be good and by looking at the baro readings is the only way to tell

 

[Kevin Palmer]

Good post Rich.



And I fully agree with it as well.



Since both banks are affected, you need a common cause. And I also am betting it will be vacuum..