if you have these codes do some research on fuel trims and use that to diagnose your problem. you'll need a live OBDII reader which you can get for about $25 plus an app on your smartphone or laptop, depending on which one you buy. There are several good channels on youtube that teach you about fuel trims and OBD diagnostics. I have recently found scanner danner, autoeclinic, schrodingers box, and fordtechmakuloco. all seem to be very knowledgeable.

most of the forums I read are people guessing at the problem and replacing parts until they fix it or searching for leaks. listen to those guys listed above and use the diagnostic tools. I'm not going to talk about my issues because I'm not sure I've found the right one yet. just a suggestion that before you throw money at the problem you should spend some time on the interweb and use a code reader.

hope this helps. I'm a wannabe mechanic who is always looking for good advice. This problem with F150s seems to be widespread and I haven't seen a good cure-all yet. however, you should clean the MAF sensor with some dedicated MAF sensor cleaner that you can buy for under $10. Cheap solution and good youtube videos on how to do that. I can give you some tips as well. it seemed to help my problem but it's only been a day.

Update: 2 days after cleaning MAF sensor and CEL is off by itself. Plan to do some more diagnostic testing this weekend. Borrowed a couple Mityvac test kits to check fuel pressure, vacuum, and EGR.

 

A couple of real common causes of a lean condition in both banks, specifically on our trucks are problems with fuel pressure from the fuel pump driver module. You can watch rail pressure with the scanner. I personally had another common situation where a near impossible to reach vacuum hose pops off the back of the intake. Its quite difficult to find. I have heard some people on the forum have purchased telescopic cameras to inspect and validate.
put them

There is a small red line wrapped in black loom about 1/8" inside diameter that runs across the fire wall and plugs on the back of the intake, slightly off center towards the passenger side. I was able to reach it by pulling the fuel rail, and throttle body. That said it was still a tight fit.

 

Thanks Nick. I plan on checking the fuel pressure next time I get a chance just to see. The truck is running pretty well now but I'm still not convinced. Plus I like doing the diagnostic work.

 

We're not talking about the PCV elbow at the back of the throttle body, correct? To what does this red-wrapped line connect? I'm mega-interested. Jose, let's compare notes, man! I'm fighting a battle as we speak. I'll follow you down the diagnostic rabbit hole. ...seriously though. Post your problems away

 

I will take some pictures when I get home. Its the smallest diameter hose that independently runs from the driver, and passenger side. They meet and take a 90 degree turn downward behind the manifold. The inner tube is red, but has a black protective loom.

 

Got in there again and found the red vacuum line you're talking about. We likely have different setups on our different engines. On a 5.4L 2v, the fuel pressure regulator routes back to the throttle body and shares a fitting with the EGR solenoid vacuum line, as well as one more line. This elbow sits above and forward of the brake booster vacuum line on the T/B.

 

Thats the one. You are correct it starts on the fuel pressure sensor on the 3v motor, as well. It however doesn't connect to the throttle body on my truck.

 

Hey guys,


The vacuum line you are talking about supplies vacuum FROM the lower "belly" chamber of the intake manifold TO the fuel pressure sensor on the driver's side Fuel Rail. The other one running up the passenger side of the TB is plugged on mine. (I guess some models might have two fuel rail pressure sensors??) But The fuel pressure sensor's reading is "relative" to the amount of vacuum. I presume the ECU calculates that it needs less fuel pressure if vacuum is higher - or some thing like that.

Anyhow - the rubber part that plugs on the IM port gets brittle and cracks. A picture is worth a 1000 words - see the great photos of this line in this post: http://www.ford-trucks.com/forums/10...ml#post9929436


Try spraying starting fluid (Ether) down between the firewall and IM (and ALL around the intake) - preferably while monitoring O2 sensor graphs or readings. If there's a leak the O2 readings will INSTANTLY GO CRAZY if there is any vacuum leak. If you don't have that capability - you probably can tell a difference in idle if there's a leak.


ALSO - if your O2 sensors have > 100K miles on them, I am very much in favor of preventively replacing all four. They aren't that expensive and the ENTIRE closed loop system is based soundly on the readings from them. I believe they get "lazy" and "out of calibration" with age. AND (perhaps because they get coated with exhaust contaminants) their drift is in the direction that decreases their oxygen sensing ability and therefore increases fuel trims to compensate. Even if their reading is within the normal range, I know of no simple way to verify that they are producing .45 volts (450 millivolts) at the optimum 14.7:1 ratio.


Good Luck

 

Just want to close out the thread for any future readers. This concludes about three weeks of near-daily troubleshooting. Sorry for the long post, but there's some good info here that I would have liked to find all in one spot when I was fighting this battle.

A new Dorman intake manifold (part number 615-188) ended up being the fix for my high fuel consumption at idle. You can find a lot of the following information in the many other threads out there, but I'll collect it here and summarize my situation:

The MIL would come on accompanied by a P0171/174 code for two lean banks. This would only happen after a cold start (55F) and about 5 minutes of low-speed driving (<30mph). I could induce the light by shutting down and immediately starting back up after that quick 5 minutes of driving.

I had NO ROUGH IDLE or hesitation to speak of. Here is what I advise based on this experience.

1- Get a scanner with real-time and freeze-frame capability. I found this one for $47 and it was THE REASON I was able to get this truck fixed. You need to be able to read Short Term Fuel Table data when you are searching for vacuum leaks with the spray method. The computer compensates too quickly to allow the engine to race when you introduce a richer mixture.
Also, reading the Long Term Fuel Table data was necessary in determining the total fuel addition (by adding STFT to LTFT). I was finding LTFT at 29.7% during troubleshooting. YOU NEED THIS SCANNER.

2- Start simple and don't shotgun parts at your truck. When you get frustrated, everything starts seeming like a good idea to replace. I should not have changed my MAF sensor. It was reading 0.49 lb, when the prescribed reading was .657. The voltage was .25V low. But the MAF was doing its job. It wasn't reading full airflow because the remaining 0.16 lb of air was leaking in AFTER THE MAF SENSOR. In most cases, you can prove something is faulty before replacing it.
Look for O2 sensors to be cycling on your reader. If they are, search elsewhere. If your MAF is reading low, keep it in mind and keep searching for leaks.

3- Vacuum leaks are the most common cause for a combined P0171/P0174. The most thorough way to approach it is to start at the air filter and methodically work your way back. Here's are some things to look at, remember them when you are spray-checking as well:
-MAF wire harness boot for tight installation (this is located just to your left of the air filter quick release clamp, on the bottom side of the duct)
-Air duct hose clamps (these are the clamps secured with 8mm drive hose clamps--there is one at the filter end and one at the throttle body)
-Two large vacuum hoses on driver's side of air duct, forward of the throttle body (check for a tight fit)
-All hose connections on the throttle body need to be tight. If they slide right off, replace them
-DPFE sensor hoses, 2 (the DPFE sensor is mounted on a bracket just to your right of the throttle body, just forward of the EGR valve)
-DPFE solenoid vacuum lines, 2 (located on the same bracket, just to the right of the throttle body)
-PCV VACUUM HARNESS. There is so much information out there about the elbows for the PCV harness, and if you're reading this, you've probably already checked that harness out...ESPECIALLY the big elbow attached to the very center of the back of the intake manifold, way back at the firewall. BE SURE you have checked these elbows with the ENGINE RUNNING. They can collapse under vacuum. Also, get a Motorcraft PCV valve and grommet.

If all these items pass your inspection, the next step is to start spray testing:
1) Hook up your scanner and monitor the STFT1 and STFT2. Use CRC Electronic Contact Cleaner; it is easier on rubber components, intended for electrical components, and still highly combustible.

2) Using short bursts, 3-4 at a time, shoot the above mentioned areas with the straw attached to focus the spray. You are watching for your STFT values to decrease in value (a sharp 4% or more). It will be a noticeable change when you find a leak.

3) Spray both ends of all the hoses mentioned above.

4) If you haven't made any finds on the air duct, and vacuum hoses attaching to the throttle body:
-Don't forget the bottom edge of the mating surface of the throttle body
-Move down to the intake manifold. Spray down around the bottoms of the fuel injectors (watch those STFTs!).
-Still nothing? Now spray UNDER the intake manifold. There is a big, open cavity located just behind the alternator. Spray back under there. This was where I finally saw the STFTs come crashing down.

If you have found your leak here, I figure you have two options:
1- Assume the intake manifold gasket is bad and go for replacing it
2- Decide that either the gasket is bad or the manifold is cracked OR BOTH. In my opinion, I'd rather replace both with the same amount of work than find that the gasket didn't fix it and have to do the whole job again.
-The top-quality OE gasket from Felpro is $60 on Rockauto.com, and $84 at Autozone.
-The aftermarket intake manifold from Dorman is $170 from Amazon and comes with better gaskets

Additionally, the factory intake manifolds are notorious for leaking coolant at the crossover ports to the passenger cylinder head. I say just replace the manifold.

That job, while not easy, is very manageable and doable when you take your time, label everything as you disassemble, and obey the torque patterns and specifications.

There are some great write-ups on how to accomplish that job, which I will not cover here. But do your homework and preparation before you jump in and you'll be in great shape.

Hopefully someone out there finds this useful down the road. There is just no reason to surrender to the infamous 171/174 nightmare. You can fix it! Good luck!