I’ve been battling fuel delivery issues since the minute I got this truck. It runs fantastic on the rear tank but the o rings in the steel connector have degraded and it leaks a fair amount of fuel or it feeds back to the front. My front tank doesn’t leak or seem to backfill but the engine also sputters on it intermittently. It is particularly noticeable at idle and under load and sometimes causes a poor 2-3 shift (once again only on the front tank). I replaced both pumps about 10 moths ago with crappy eBay ones (obviously a bad idea). I had been having these issues but received no codes for them up until today where I tracked down the front tank pigtail and noticed that right before the wires enter the connector some PO had cut them to test at some point. I had a spare connector lying around and after using some heat shrink crush connectors I was able to successfully wire it back up. I drove it around and it felt a bit better especially at idle. I finally picked up codes as well as it hadn’t thrown any before. I have a p0171 (fuel injection bank 1 lean) and a p0174 (fuel injection bank 2 lean). Any advice before I make a purchase on new pumps? I figure a good test would be to clear all codes and try to run on the rear tank and see if they reappear (thoughts on this test?). Any advice is appreciated regarding fixing my issue and new pumps.

also not that it is relevant because the bank tanks works fine, but I have also checked the relay in the PDB and it is good

 

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P0171 and P0174 Lean Trouble Codes

What are P0171 and P0174 code definitions?

P0171 - System Too Lean Bank 1
P0174 - System Too Lean Bank 2

What Does P0171 and P0174 Mean?

DTCs P0171 and P0174 are generic codes that set when the feedback on the engine's air/fuel mixture becomes too lean for the Engine Control Module (ECM) to correct within its normal operating range. A lean mixture is a mixture that has too much air or not enough fuel. The ECM sets a target air/fuel ratio and monitors it using oxygen sensors and on newer vehicles air/fuel ratio sensors. When the ECM sees the engine running lean, it will add fuel and display the correction as a positive fuel trim percentage. If the correction goes past the ECMs predetermined range in the positive (add fuel) direction, the ECM will set a lean DTC P0171, P0174, or both.

P0171 and P0174 Symptoms

• Check Engine Light
  
• Low engine power
  
• Poor idle
  
• Stalling
  
• Engine misfire
  
• Spark/Engine Knock
  
• Possible hard start or no start
  
  
  Tip : Vehicles can experience one or all these symptoms depending on severity of the condition

What Causes P0171 and P0174 to Set?

• Vacuum leaks, intake air leaks: Vacuum leaks allow un-measured air to enter the engine, this air is unaccounted for and causes the engine to run lean. Cracked or broken vacuum lines, faulty intake gaskets and intake tubing are all common sources of vacuum leaks.
  
  
  Tip : Vacuum leaks are also commonly caused by components that use or regulate engine vacuum, such as purge solenoids, brake boosters and PCV valves
• Incorrect air metering, Faulty Mass Air Flow (MAF) sensor: If the air entering the engine is measured incorrectly, more air can enter the engine than the ECM calculates for. An inadequate fuel charge will then be delivered, and a lean air/fuel mixture will be created. The leading cause is a malfunctioning MAF sensor, due to failure or being dirty.
  
  
  Tip : A faulty or skewed coolant temperature sensor and/or air temperature sensor can cause certain systems to mis-calculate air/fuel mixtures, resulting in P0171, P0174 DTCs.
• Malfunctioning oxygen (O2) sensor or air fuel ratio (A/F) sensor: The ECM uses O2 sensors and A/F sensors to test the exhaust gas, this provides feedback on the air/fuel mixture delivered to the engine. If the sensors read excess oxygen in the exhaust, it tells the ECM the engine is running lean. Therefore, a faulty O2 sensor or A/F sensor can provide incorrect feedback to the ECM and create a false lean condition.
  
• Low fuel pressure, incorrect fuel flow/delivery: Low fuel pressure or poor fuel flow causes less fuel to be delivered to the engine than commanded by the ECM, resulting in a lean running condition. This can be caused by several things such as a faulty fuel pump, dirty fuel filter or clogged fuel injectors.
  

How to diagnose P0171 and P0174 DTCs?

Recommended tools

• Scan tool (Autel scan tools that show data PIDs)
• Flashlight
• Hand tools
• Multimeter (Astro multimeter)
• MAF sensor cleaner (CRC MAF Sensor Cleaner)
• Soapy water spray bottle
• Fuel pressure tester
• Smoke machine

Diagnostic checks

Tip : See if any other DTCs are stored, additional trouble codes may help determine root cause of P0171, P0174 DTCs

• Inspect for vacuum leaks: Visually inspect and listen for any obvious engine vacuum leaks, look for any broken or cracked vacuum lines, pay close attention to brake booster and PCV hoses. Check that air intake tubing is installed properly and is not torn or damaged. A smoke machine may be needed to locate hard to find leaks.
  
• Check Mass Air Flow sensor: Remove the MAF sensor and look for signs of contamination, debris that makes it past the air filter or oil from an aftermarket air filter can stick on MAF sensor and cause inaccurate signals. If dirty, clean sensor using a quality MAF cleaner. If a scan tool is available, check MAF sensor signal reading and compare to vehicles listed specification.
  
• Inspect Exhaust: Leaking exhaust can affect O2 sensor readings. Visually inspect and listen for exhaust system leaks. Look for any cracks or damage to exhaust pipes and any black soot marks. These are tell-tale signs of a leaking exhaust. For hard-to-find leaks, spray soapy water on suspected locations and look for bubbles to pinpoint leak.
  
  
  Tip : Exhaust leaks behind the rear O2 sensor will not affect air/fuel mixture
• Check oxygen sensors and/or air fuel ratio sensors: Using a scan tool, monitor the signal voltage of the O2 sensors and/or A/F sensors and make sure they are operating correctly. If a scan tool is not available a multimeter can be used to read signal voltage. Every vehicle operates differently so you should consult your vehicles service information to obtain the correct procedure in checking these signals.
  
• Check fuel pressure: Obtain a fuel pressure reading and compare to the factory listed specification. Some vehicles are equipped with a fuel pressure sensor and fuel pressure can be read using a scan tool. If your vehicle does not have this option, a fuel pressure gauge will have to be installed to read fuel pressure manually. Be careful, as many modern vehicles use a gasoline direct injection (GDI) system and run at extremely high pressures. So be sure to check service information for the correct procedure.
  

How do I repair a P0171 or P0174 DTC?

Due to the number of components that are involved in the operation of your vehicles engine management system. Proper and accurate diagnosis are required to pin-point the cause of P0171 and P0174 diagnostic trouble codes. As listed above there are several systems involved that could potentially be malfunctioning, so guessing could become costly.

 

If you suspect you have bad pumps or low fuel pressure, the first thing to do is to check your fuel pressure. Here's how. https://www.ford-trucks.com/forums/1...rd-trucks.html

 

Thank you both for such detailed information. I read through your thread Prototypemech and will run that test today in both tanks. I have a diesel compression tester which I think has a schrader valve fitting but if not I’ll use a bike pump or go get a real fuel pressure tester. I will report back once I have tested. On another separate note is there any diagram out there that shows the vac routing? Some PO went haywire and chopped stuff so im not sure where some stuff goes. I have some new vac line ready to go but I wanna make sure the routing is correct.

 

So I have done the following thus far:

Originally replaced the fuel pumps back in September/October of last year with garbage eBay pumps. Had an issue where the spring slips tore out of the front tank return line and replaced that. Had an issue with the rear tank send line where the o ring tore out. I have not carefully checked but I am sure the shuttle valve is faulty in at least the rear tank or there is still a leak. I am looking to get just one of these tanks to work as I am done for the time being with this fuel system (that simple mech fuel pump on my 7.3 IDI spoiled me). I replaced the fuel pump wiring connector to the front tank after someone had cut the insulation to test the wires. After this was done I got bank 1 and bank 2 lean codes (p0171 and p0174). I tested the fuel pressure of both tanks today and both were within spec, however on the front tank only there was an instance where the needle fluttered and the pressure dipped a bit. My question now is, is it possible to replace the orings within the sending/return lines? (As in maybe a NOS part online) or should I go ahead with a new fuel pump on the front tank? I am also happy to try running a current test to the harness but am unsure what that would look like and have been unable to find such a test in my haynes manual.

 

I also need to add that the fuel evap line on my front tank is not hooked up and there is a small hole in the top of the tank unsure if that was a PO drilling into the tank but I was wondering if those would have any relation to my issue. I have also observed that the rear tank returns to the front tank. Would it be an okay fix to plug the return line so that it doesn’t feed into the front tank or would this just build up pressure and go nowhere?

 

What were the pressure readings at idle with the vacuum attached to the fuel pressure regulator? What was the pressure with the vacuum line removed? What was the pressure with the engine under load?

We ask this because more than a few time someone has responded with "in specification" but it turns out it really is not.

 

Lean on both BANKS means all 6 cylinders (1-3 and 4-6) are running lean.

Lean on both TANKS means both fuel pumps (or the filter, possibly) are underperforming.

Lean on TOM HANKS and you'll probably have charges pressed against you.

t
didn't mention SPANKS until... well, here.

 

I used a tire gauge to get my pump readings for the front pump hooked up to the Schrade valve and got a reading of about 40psi KOEO and then it fluttered down about 5-7 psi with the engine running under load. My solution to this has been to plug the lines with the old fuel pump I removed a while back. I the the connectors off of it and welded the back of them to create a plug that blocks the factory line with factory connectors. I have the front tank out right now and am going to look into a quality pump for it. Are there any current tests I can run to the fuel pump connector coming out of the wiring harness?

 

Those are too low for a 4.9L engine. It runs at a higher pressure than the V8 engines. Perhaps you have the wrong fuel pressure regulator. Or the pump is weak.