I have a 2004 F150 with a 5.4L 3V about 130K.

I've been fighting lean codes for a month now. Both banks. Replaced all O2 sensors and the MAF with motocraft parts.

I am now watching codes and outputs in real time with the Torque app.

Upstream O2 sensors seem to function normally (vary between .1 and .9) above 2K rpm.

Idle is very rough and eventually (3 minutes) stalls. Output voltage from both upstream O2 sensors drops to .01 on both sides at idle. If I punch the throttle at idle values jump up to .8 or .9 for a second then back to .01. I'm convinced O2 sensors are working properly. If I let it idle long enough it throws both P2195 and P2197 upstream O2 sensors stuck lean. I can drive it fifty miles (probably further) without a code but as soon as I let it idle for a few minutes it throws the codes. Always both of them.

I've researched a lot here and believe it must be:
A) a vacuum leak
B) a fuel delivery problem.

I have port blocked each hose/system from the intake and not found a vacuum leak or been able to improve the idle or o2 sensor readings.

Haven't changed the fuel filter yet but there is no fuel delivery problem under heavy load conditions so I assume there is no fuel delivery problem.

Where are the most likely vacuum leaks on this engine? Unfortunately it doesn't have the rotten elbow behind the manifold, apparently they changed that before my truck was manufactured.

Am I missing something about the fuel delivery system? I regularly clean the injectors. Is it likely that there are enough bad injectors to cause both banks to be lean?

Is three another sensor that may be the likely problem?

I appreciate your thoughts and advice.

 

Have you cleaned the maf?
By any chance you have a cold air intake on the truck?
As for no codes while running, these trucks vary fuel pump speed, so if there is a restricted fuel filter it might not be a problem if the pump speeds up.

 

I replaced the MAF with a new one.
No cold air intake. All stock.
I was not aware of the variable speed pump. I will change the filter.

 

It might be the FPDM. It has a history of corrosion.

 

Okay, I read about that.
Seems I should be able to monitor the fuel pressure by odbII need to look in to that. What should fuel rail pressure be at idle?
Thanks.

 

Update: Changed the fuel filter. Didn't solve the problem. Low (650 rpm) idle and eventual stall. Lean codes are back. Arrrgh....

 

Well you could go old school and pull out the starter fluid and try to find a vacuum leak.

 

what's the codes????

you maybe wasting money by chasing it with parts...

could be an exhaust leak too before the o2's

 

P2195 and P2197

 

thanks...missed them

 

No problem!

 

have you sprayed wd-40 or similar around the intake or PCV hoses to see if the RPM's rise? If there is a leak after the MAF, you'll get a lean code.

I had a P0171 [System Too Lean (Bank 1)] code on my truck this weekend after a new timing set. A new set of plugs fixed it.

 

Thanks for the responses, I've been away for a couple of days.
Codes are P2195 and P2197.
I've ruled out exhaust leaks. There are none.
Have tried starter fluid. No change in idle. Going to try it watching the O2 return voltages to see if they spike.
May be the intake manifold, trying not to think about it
In any event there is too much air and /or not enough fuel at idle.
Another session this weekend.....

 

Have you looked near the throttle body well, I think there is a gasket between it and the intake. Easier to look at than the intake manifold. Other than that it seems you have almost checked every possible cause.

 

I know this is an old one but hoping to reach OP to see what resolution was. I'm having the same issues after checking all he has.