cms81586

Hey folks! New member here having some issues with my 2004 F150 4.6L. Recently on a camping trip I noticed a significant loss of power and torque...especially on the low end. The check engine light came on for about an hour and then shut off. On the way home I stopped at an Advanced Auto to have the fault code read. I got P0171 Bank 1 Too Lean.

Here's a summary of the symptoms:

-Slow throttle response
-Power / torque loss (more noticable once the engine warms up)
-Loud Hiss before engine RPM increases when revving the engine (not sure if this is normal for the 4.6L or not
-Downshifts on hills and even at high RPM's (4000) it still has no power
-Still have Fault Code P0171: Bank 1 too Lean
-Found no vacuum leaks with starter fluid
-When powerbraking on a gravel road (only to test amount of torque...I don't ever do this) the motor does not produce enough torque to overpower the brakes like it should...boggs at 2000-2300 RPM.

I've already tried:
-Cleaning the MAF Sensor (CRC Electrical Contact Cleaner)
-Checking Vacuum Hoses and Intake Manifold for leaks with starter fluid with truck at an idle (found no signs)
-Truck has a new fuel and Air filter



Tonight I'm replacing:
PCV Valve
Oil
Oil Filter
Spark Plugs
and I'm going to try some fuel injector cleaner as well.

I'm still well below what I'd be paying just to get diagnostics done at the dealership...so I'm not complaining. Looking for any suggestions and similar experiences.


CMS

Turkey Hunter

When you buy an injector cleaner get gumout that stuff works great.

faniman57

I have a 2008 4.6L with 27xxx and I'm experiencing the same thing, only theres like a hiss from the engine between 1200 and 2000 rpms. Ive had a major loss of power, and its started to shift really hard. The engine seems like its working really hard to get up to speed, but with no success. I just changed the oil and filter not even 200 miles ago, the air filter was replaced about 3200 miles ago. I've heard that diff fluid should be changed every 30k, could that be the problem?

CaptainPipp

faniman57 how did you fix it?

faniman57

Honestly, I just kept driving it. It seems like a dumb idea, but I thought maybe it needed to be cleaned out. I floored it and got it up to 100 to try to get her lubed up again. It seemed to do the trick.

A fair warning though, when the 4.6 gets up to 5000 RPMs, its almost like

cleveland lotlizards

Have you cleaned the Throttle body ? They tend to get pretty gummed up