Super Lean E150

Derrick Diagnostician Kentucky Posted   Latest  
Unsolved
Driveability
2008 Ford E-150 4.6L (W) 4-spd (4R75E)
P0171 — System Too Lean Bank 1
P0174 — System Too Lean Bank 2
Fuel Trims Maxed Lean At Idle Some Waht Lean Off Idle

at idle I am +20 both banks I am around +15 off idle. ive checked fuel pressure, checked over and over for vacuum leak systematically blocked off lines used some machine sprayed brake clean. i can only find a small leak in weep hole of EGR diaphragm doesn't make a big difference when I block it off. checked for exhaust leak nothing MAF reading is on par around 4.5 grams at idle. Replaced plugs idle slightly rough i was wishing on a star hoping maybe we had some misfires not getting counted not uncommon with ford o well needed a set anyway. O2 seem to respond well plus for both to be skewed would be unlikely. Im sure im missing something… hell i feel like i am… any suggestions thanks

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Rudy Technician
Utah
Rudy
 

Check fuel quality.

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Andrew Technician
Ohio
Andrew
 

While checking fuel quality, also check the fuel for Alcohol content. Is it E85?

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Andrew Technician
Ohio
Andrew
 

Is the air cleaner/air filter housing installed. On Ford vans, if the air filter ‘EGG' housing is open, the engine cooling fan will mess with the MAF.

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Elon Owner/Technician
North Carolina
Elon
 

Check fuel quality, Ethanol content. Also double check PCV system. Rotted hoses, things of the sort.

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Dwight Owner/Technician
California
Dwight
 

Does it have the correct style air filter installed.

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Glenn Owner/Technician
Texas
Glenn
 

Hi Derrick, Replace the inline fuel filter would be the first thing to address. After that test fuel quality, volume and pressure. Being a Ford 4.6 the PCV soft hoses are bad about collapsing and sucking air, this can be hard to hear and find if the vans engine cover is still in place.

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Rusty Owner/Technician
Massachusetts
Rusty
 

Lean at idle is not a fuel supply issue.

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Ray Diagnostician
Ontario
Ray
 

Ck fuel pressure and volume. Do the 02s show rich at WOT, when driving thru the 1st to the 2nd gear shift.

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Rod Diagnostician
California
Rod
 

Maf drive full throttle under load test ( adhere to safety precautions ) should flow 184 grams per second , if maf flows correctly with the + trims you show (also graph post cats o2 sensors when performing maf test to confirm lean mixture) fuel volume delivery and or or fuel quality is the next test. (misfire monitor will most likely suspend if under ¼ tank)

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Rusty Owner/Technician
Massachusetts
Rusty
 

If it worse at idle and gets “less lean” with throttle opening and is normal under load, you almost certainly have a vacuum leak.

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Juan Diagnostician
California
Juan
 

I’ve had a Ford with good g/s that was also lean, what I found was that hertz where at 120 at sea level when they should be at around 159. i would recommend to check how you hertz and compered them to specs depending of the level you are located

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Helpful
Mark Engineer
Colorado
Mark
 

Derrick So many outstanding ideas in the thread so far. Since you have indicated lean at idle, does freeze frame support this? (probably under generic, you'll get one freeze frame data capture). Do not clear codes (or you'll have to accumulate drive cycles again), bring engine speed up to about 2,000 RPM. Do the LTFT1 and 2 approach zero?. If so, I would agree with most in the thread, the…

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Rod Diagnostician
California
Rod
 

I have experienced the smoke machine push and seal the elbow but engine vacuum opens it back up

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Michael Owner/Technician
Utah
Michael
 

I'll second the vacuum elbow. I've also seen the dipstick tube break from the bracket and create a slight vacuum leak.

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Martin Diagnostician
Texas
Martin
 

Is 4.5 g/s at idle really ok? I believe the g/s at idle should be roughly 1.25% of engine displacement. This is not exact, but more a general rule of thumb. If I see less than engine displacement I start looking at the maf. What does it do under load? Do the o2's maintain 800mv on a hard acceleration? VE test would be in order. What does the load say on a WOT stab at the 1-2 shift?

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Danny Technician
Wisconsin
Danny
   

I have seen a rubber vacuum fitting on the back of the engine with a hole in it or popped off the vacuum port. Spray some brake cleaner in the back of the intake manifold just above of the bellhousing.

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Blaine Technician
Iowa
Blaine
 

That was my initial thought as well. Seems kinda low. I’d be curious if it’s only lean at idle like the other guys stated.

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Robert Technician
Michigan
Robert
   

O2's monitor would probably fail before those trim code codes if those were issue set, unplug MAF see what changes , MAF & TPS should mirror each other graphing … purge valve also in the equation at idle …

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Mark Engineer
Colorado
Mark
 

Robert I forgot about EVAP circuit and purge valve. But I wonder, if the purge valve were allowing fuel-tank-rich vapors, wouldn’t it run rich? I’m probably not thinking straight. Your thoughts?

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Robert Technician
Michigan
Robert
 

Initially that's true but purging uses up fuel vapors quickly & who knows might sticking solenoid sucking fresh air , it's just on the quick check list blocking it off & eliminating a possible cause if its sitting there bleeding internally like a blown PCV elbow .

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Jose Technician
California
Jose
 

Does this van have EGR? If so can you check the pipe temp and make sure it’s not flowing at idle.

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Sean Technician
California
Sean
 

Wouldn’t that make it rich, since your are displacing the air in the combustion chamber with spent exhaust gas?

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Jose Technician
California
Jose
 

I don’t think it will make it rich or lean. I think the trims would be normal since It has a MAF. It is likely not the issue with Derricks van now that I think about it.

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Sean Technician
California
Sean
 

Yea plus it would likely code for excessive egr flow

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Timothy Owner/Technician
Wisconsin
Timothy
 

MAF is way under spec. Needs to be above the liter displacement of the motor, at hot idle in Park…so yours should be at the very least, about 4.7 g/sec. 4.5 is several percentage points low.

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